increasing the firing time. The opposite is true when the kilovolt
is high. We learn that kilovolt is a necessary parasite, robbing
from the burn time in the combustion chamber. Kilovolt does
causes the kilovolt demand to increase even more in proportion.
combination of worn spark plugs and lean mixture.
Replacing a part to see if the misfire goes away without knowing the cause is a
fruitless exercise. Crossfire occurs when kilovolt is driven high beyond the capacity
of the insulation. Then the spark is enticed to find a path to ground outside the
combustion chamber. When that happens, there is no HC present outside the
combustion chamber to sustain conductivity resulting in high resistance creating
shorter firing time at a higher kilovolt level.
For practical purposes, there is no current flow until the plug fires as indicated by
the firing time. When the coil output runs out of energy, the residual energy dissipates
into oscillations. Because hydrocarbons (fuel) are conductors, they not only assist in
the ionization process, but also affect the conductivity during firing time.
Author: WisdomAugust Time: 2017-8-5 08:16
How Do We Know It Is a Plug Wire?Let us assume a cylinder at idle showed abnormally high kilovolt, and the firing time seemed
to be shorter compared to the other cylinders. We need to find out where that high kilovolt is
created, internally or externally. Play with the throttle, accelerate and decelerate and watch
the response. If the kilovolt stays high, this indicates that the greatest gap was external.
How should the scope respond to rpm increase?
At 2,000 rpm, the timing advance is between 30 and 40 degrees BTDC. At that time, the
piston barely starts the compression stroke resulting in less compression when the plug
fires. Therefore the reduced kilovolt tells us that the timing advance is functional and there
was compression. We have verified the greatest gap is indeed in the combustion chamber
and not external.
Author: WisdomAugust Time: 2017-8-7 13:21
What About Fouled Plugs?Scope analysis has a lot to do with common sense. Let us imagine what a fouled plug looks like on the scope. No picture illustration to memorize, just use your imagination. There is no spark gap and therefore no nose or residual energy left. Because carbon resistance replaces the spark gap, the coil energy is drained off, as indicated by a curved slope from the kilovolt spike to the dwell line. Resistance of carbon foul could be as high as 2 Megaohms demanding more kilovolts than, for instance, a wet plug caused by a dripping injector. How do we know the difference? Very simple!
Author: WisdomAugust Time: 2017-8-8 10:04
Edited by WisdomAugust at 2017-8-8 10:07
Leaky Injector
At low RPM, it might look like a fouled plug, but at higher RPM the dripper might start firing
because there are fewer drips between firing events. But when this cylinder fires, the fuel
mixture is still rich and the scope shows a lower kilovolt plus a longer firing time with hardly
any nose. The computer looks at that dripper as too rich and subtracts fuel, driving the other
cylinders extremely lean.
There is one exception: the cylinder next in firing order, which benefits from the overflow of
the dripper. With computer controlled engines, total engine analysis of all cylinders tells us
the complete story and verifies diagnosis, and that is important to save valuable time.
Author: WisdomAugust Time: 2017-8-9 08:20
[attach]1654[/attach]
Author: WisdomAugust Time: 2017-8-10 08:23
Exploring Firing TimeThe coil output is designed to maintain the firing event for as long as there is controlled fuel in the combustion chamber.
Because a collapsing magnetic field determines coil energy, engine RPM or load doesn't affect it. The firing time indicates
how well this energy is used in burning the fuel mixture. After establishing the validity of the electrical components at
idle, firing time is our ruler to measure conductance.
Because all cylinders and injectors on that engine are created equal, comparing the firing pattern is the easiest method
to seek out the cylinder that is different.
Author: WisdomAugust Time: 2017-8-14 09:20
Lean injector: In following picture, we noticed that cylinder B has a shorter firing time.
The absence of hydrocarbon is particularly visible at the end of the firing time, where it
terminates with a high nose. It is as if the coil is saying, "It's not my fault, there is plenty
of energy left." However, there is something else to observe in cylinder B. The evidence
of a lean condition already starts at the beginning of the firing time with a higher kilovolt
demand and higher firing line starting point in comparison.
Author: WisdomAugust Time: 2017-8-15 11:43
[attach]1669[/attach]
Author: WisdomAugust Time: 2017-8-16 08:14
Comparing with a good performing cylinder at the same speed or load is essential.
How do we know that "A" is OK? First, note that there is no coil energy wasted in high
kilovolt demand. Second, consider the smooth conductivity of the firing line of total
combustion as long as there is coil energy available. Finally, the nose tells us to what
extent coil energy is used up to burn all the fuel. This is a perfect match of air, fuel
and spark duration.
We do want to know the where, when and how before drawing a conclusion. Besides
location, it helps to know how many cylinders are affected and what the RPM or load
was when the problem occurred. It does not take any skills of scope pattern interpretation
to identify a shorter than normal or greater than average firing time to pinpoint the oddball.
Any short spark duration indicates a higher resistance either due to high kilovolt or reduced
HC. A longer firing time indicates a lower than average resistance.
Author: WisdomAugust Time: 2017-8-17 08:26
Helpful Hints in Scope Pattern Interpretation Anyone who knows Ohms Law understands that the effect of resistance is in direct proportion
to current flow. When we have a poor connection at the battery post of as little as 0.01 ohm
with the headlights turned on, it creates only 0.1 voltage drop — not even noticeable in brightness.
However, during cranking, that same resistance at 300 amps cranking load means 3 volts less
at the starter. This certainly will slow down the cranking speed. This also holds true for air flow
or fuel flow. A kink in a garden hose does not make much difference if you want a cup of water,
but it becomes a problem when sprinkling the lawn. A fuel filter restricted at 80 percent will not
make any difference at idle, but the car will not have the horsepower to make it uphill.
The point is simply that testing under load makes all the difference to complete performance
analysis. Because you have the scope hooked up, it might take less than a minute in the bay
or up to 20 minutes on a test drive. There are different options or methods of testing under load,
but they all have two things in common. First, it needs to be done with someone in the driver
seat. Second, the leads need to be long enough to reach the equipment inside the vehicle.
Author: WisdomAugust Time: 2017-8-18 13:25
Test Results Under LoadResistance and restriction or obstruction all mean the same thing and will have the greatest
negative effect when the demand for flow is high. Let us explore examples.
Restricted exhaust: When the engine cannot exhale properly, all functions are affected.
The firing line on the scope showing perfect at idle, becomes ragged and shows turbulence
progressively getting worse under load disturbing all cylinders. Plus, EGR is doubled or tripled.
Under normal conditions, the EGR valve re-circulates about 7 percent of the exhaust gasses
into the intake. However, with even a small exhaust restriction this might increase to 30 percent
or more. Momentarily inhibiting the EGR valve from functioning, while watching for improvement
on the scope pattern, is one way to verify restriction. Restriction will cause reduced volume and
is not a lean mixture as it is sometimes called. It is not affecting the air/fuel ratio.
Author: WisdomAugust Time: 2017-9-2 16:33
Edited by WisdomAugust at 2017-9-2 16:35
Dual exhaust:
This, from separate banks, can play tricks if one bank is restricted. The good (non-restricted) bank
will look extremely lean on the scope pattern with a high nose, while the restricted bank seems to
have a richer fuel mixture with hardly any nose. Let us assume that bank No. 1 is 50 percent restricted.
The MAF sensor will report this reduced flow as 100 plus 50 divided by 2 is 75 percent of total flow to
the combined banks. The computer distributes an equal amount of fuel to both intake manifolds.
The good bank No. 2 inhales 100 percent air and gets 25 percent less fuel allotment. The restricted
bank No. 1 inhales 50 percent air and gets the same amount of fuel. That is 25 percent more fuel than
this bank requires. See if you can find a lean cylinder and a rich cylinder in the illustrations that will
match bank 1 and bank 2.
Author: WisdomAugust Time: 2017-9-4 08:13
Worn Cam Lobe:
This problem is not a daily occurrence, but we're exploring how to interpret what the scope
is trying to tell us in the waveforms. Following picture looks almost similar to the lean injector
in picture 4 or picture 7, but the difference is in the kilovolt demand and the level where the firing
line starts. We need to compare this with a good cylinder (see No. 5). This is a case of reduced
volume of HC and not a lean air/fuel ratio.
Author: WisdomAugust Time: 2017-9-5 15:52
Edited by WisdomAugust at 2017-9-6 15:34
Worn Cam Lobe
[attach]1689[/attach]
When there is less volume of both air and fuel, there is going to be less compression and
therefore a lower kilovolt demand. Misfire depends on how severe the valve lift is affected.
With a 20 percent lower cam, the misfire might occur beyond 2,000 rpm, while a 40 percent
reduction in valve lift might begin misfiring at 1,600 rpm. No lift at all obviously will be dead
at any rpm.
Author: WisdomAugust Time: 2017-9-6 15:33
Inadequate fuel supply:
Whether the reduced fuel source is caused by the fuel pump, pinched fuel line or
dirty fuel filter, the scope does not know the difference. When you take a close look
at picture 6, you will notice that the fuel starvation could be anywhere on the firing line.
The next step is a simple current test as illustrated. Under load, the engine might start
to buck and hesitate. But long before the intermittent misfire happens, indicators are
present as flashes, moving arbitrarily from cylinder to cylinder progressively getting
worse with increased load. This is where preventive maintenance pays off.
Author: WisdomAugust Time: 2017-9-7 09:03
Fuel Pump or Filter
[attach]1690[/attach]
Author: WisdomAugust Time: 2017-9-8 13:06
Misfire under load:
When a misfire code tells you which cylinder is at fault, it is like diagnosing blindfolded,
because you still don't know why, the condition when or how often it did repeat, and how
many other cylinders are close to the same ordeal. Picture 7-1 indicates that the misfire
was fuel related with only about 25 percent active combustion. We also know that it is not
an intake leak, because it appeared only under load.
Author: WisdomAugust Time: 2017-9-11 09:36
Misfire Under Load
[attach]1697[/attach]
Author: WisdomAugust Time: 2017-9-12 09:14
We can tell that it was not lean at the start, because kilovolt demand is normal and
the firing line is not elevated. We can readily see it is not a dirty screen or an odd spray
pattern. If this pattern remains permanent and does not vary, it is not cleanable and is
likely a high electrical resistance problem getting a late start. A simple replacement of
the injector would suffice. The fact that a scope can provide all that information in detail
eliminates trial and error repair methods.
Author: WisdomAugust Time: 2017-9-15 10:09
Valve seating:
This is a common but often neglected problem. When a valve is not seated,
it does not cool, which might lead to a variety of possible failures. It is easily
spotted with a scope at idle, preferably in drive. A non-seating valve, whatever
the cause, allows compressed gases to escape. Everyone knows that a burned
valve is very noticeable at idle, but at 60 mph, that small crack does not make
much difference, because there is not enough time to escape. For that reason
testing at low speed is essential.
Author: WisdomAugust Time: 2017-9-16 09:33
The other reason for analyzing at idle in drive is because the spark occurs near TDC
when compressed gas movement is at its peak. The effect of these escaping gasses
can be seen on the scope as a hash at the beginning of the firing line.
[attach]1700[/attach]
Author: WisdomAugust Time: 2017-9-18 08:09
We will see a low kilovolt because of low compression, directly followed by hash
caused by air flow distorting the spark. Depending on frequency, the problem could
be traced to worn valve guides, carbon deposits, weak valve spring or poor lubrication.
Conclusive diagnosis depends on how many cylinders are affected and if the problem
is intermittent or permanent.
The value of a scope is apparent only when the potential is fully understood. Let us
assume that every cylinder performed as it was designed. The air inhaled is determined
by bore and stroke of the piston. This air is matched with a precise amount of fuel and the
process of total combustion matches the coil output energy with very little residual energy
to spare. All cylinders are created equal and should follow that precise pattern of combustion
efficiency. Any deviation will affect the firing time and alter the residual coil energy. Because
the lab scope is time based, there is no better tool to measure, compare and display combustion
efficiency per cylinder.
Author: WisdomAugust Time: 2017-9-19 14:44
Edited by WisdomAugust at 2017-9-20 09:23
Enter the scope - it pictorially shows the changing voltage over time,
drawing a trace that accurately depicts the pattern of voltage variation.
In fact a scope is the only way that you're going to be able to look at signals
coming out of camshaft and crankshaft position sensors, speed sensors and ABS
sensors, amongst others. And it's also the only way that you're going to be able to
see the signals going to injectors, idle air control valves, boost control solenoids,
auto trans pressure control solenoids, and so on.
Traditionally, scopes have been used by mechanics to look at primary (low voltage)
and secondary (high voltage) ignition signals. And that's a valuable use for a scope.
But these days a scope is far more likely to be used to look at inputs and outputs
of the ECU. In fact, most good factory workshop manuals now show sample scope
traces, so that you can use a scope to quickly find if the output signal from the sensor
or ECU looks as it should.
Author: WisdomAugust Time: 2017-9-20 09:25
Think about this: if in a modified car you're changing those signals by
using an interceptor, just how good a job is the interceptor doing?
Does the waveform going into the interceptor from the crankshaft position
sensor look like the intercepted waveform coming out of the modifier
(except of course for a change in timing)? Or is the output waveform horribly
distorted - perhaps the cause of that Check Engine light problem that always
rears its ugly head when you have the interceptor working?
Author: WisdomAugust Time: 2017-10-9 15:53
What if you want to make a modification in an area that few other people have played with -
for example, change the auto trans pressure for firmer shifts? These days it will be controlled
by a pulsed solenoid - but actually seeing how the solenoid is pulsed in different conditions will
require a scope.
[attach]1718[/attach]
It's important to realise that scopes have a major role to play in car modification, not just in
diagnosing obscure ignition system problems....
Author: WisdomAugust Time: 2017-10-10 09:53
In this three part series we'll start with the basics of scopes. Getting your head around a signal
that's constantly varying can be quite hard to do, especially when most of us are used to reading
relatively unchanging values on a multimeter. After that we'll look at what scopes are suitable for
automotive work, then we'll get stuck into using a scope on modified and standard cars.
[attach]1719[/attach]
Author: WisdomAugust Time: 2017-10-11 10:12
The OscilloscopeAn oscilloscope is basically a graph-displaying device - it draws a graph of an electrical signal.
In all automotive applications, the graph shows how signals change over time: the vertical (Y)
axis represents voltage, and the horizontal (X) axis represents time.
But don't be fooled - this simple graph can tell you many things about a signal, such as:
The time and voltage values of a signal (how many volts and when it changes)
The frequency of an oscillating signal (how fast the voltage is rising and falling)
The frequency with which a particular portion of the signal is occurring relative
to other portions (is there a part of the signal that varies more rapidly up and
down than other parts?)
Whether or not a malfunctioning component is distorting the signal (do the sine
waves look more like square waves?)
How much of the signal is noise and whether the noise is changing with time
('noise' is normally seen as a superimposed signal - jagged edges on a sine
wave, for example)
Author: WisdomAugust Time: 2017-10-18 10:32
The generic term for a pattern that repeats over time is a 'wave' - sound waves, brain waves, ocean waves,
and voltage waves are all repetitive patterns. An oscilloscope measures voltage waves. One cycle of a wave
is the portion of the wave that repeats. A waveform is a graphic representation of a wave. A voltage waveform
shows time on the horizontal axis and voltage on the vertical axis.
Waveform shapes reveal a great deal about a signal. Any time you see a change in the height of the waveform,
you know the voltage has changed. Any time there is a flat horizontal line, you know that there is no change for
that length of time. Straight, diagonal lines mean a linear change - rise or fall of voltage at a steady rate. Sharp
angles on a waveform indicate sudden change.
[attach]1725[/attach]
Author: WisdomAugust Time: 2017-10-19 11:14
You can classify most waves into these types:
Sine waves
Square and rectangular waves
Triangle and saw-tooth waves
Complex waves
In automotive applications, sine and square waves dominate.
Sine Waves
[attach]1726[/attach]
The sine wave is the fundamental wave shape. It has harmonious mathematical properties
- it is the same sine shape you may have studied in high school trigonometry class. Mains
AC voltage varies as a sine wave. ('AC' signifies alternating current, although the voltage
alternates too. 'DC' stands for direct current, which means a steady current and voltage,
such as a car battery produces.) Many speed sensors produce sine wave outputs - this
waveform is from an ABS inductive speed sensor.
Author: WisdomAugust Time: 2017-10-20 08:18
Square and Rectangular Waves
[attach]1732[/attach]
The square wave is another common wave shape. Basically, a square wave is a voltage that turns on and off
(ie goes high and low) at regular intervals. An injector waveform is fundamentally a square wave - the injector
is either on or off. A rectangular wave is like the square wave, except that the high and low time intervals are
not of equal length. That is, the 'on' and 'off' times are not equal. Again, this is often the case with an injector,
where at low loads the 'off' time will be much longer than the 'on' time. The waveform shown here is from a Hall
Effect road speed sensor.
Author: WisdomAugust Time: 2017-10-23 08:26
Waveform Measurements Many terms are used to describe the types of measurements made with an oscilloscope.
Frequency and Period
[attach]1739[/attach]
If a signal repeats, it has a frequency. Frequency is measured in Hertz (Hz) and equals the number of
times the signal repeats itself in one second. Hertz can also be referred to as 'cycles per second'. A
repetitive signal also has a period - this is the amount of time it takes the signal to complete one cycle.
Period and frequency are reciprocals of each other, so that 1/period equals the frequency and 1/frequency
equals the period.
For example, the sine wave here has a frequency of 3 Hz and a period of 1/3 second. Some scopes can
calculate frequency and display it as a standalone number, while in other cases the period needs to be
read off the scope screen and the frequency then calculated from this.
Author: WisdomAugust Time: 2017-10-24 09:04
Voltage
Voltage is the amount of electric potential - or signal strength - between two points in a circuit.
Usually, one of these points is ground, or zero volts. DC signals are measured on a scope as
you would with a multimeter - from ground to the amplitude (height) of the signal.
Automotive AC signals are often measured from the maximum peak to the minimum peak of a
waveform, which is referred to as the peak-to-peak voltage. The peak-to-peak voltage of this
inductive crank sensor is just under 16 volts.
[attach]1740[/attach]
Author: WisdomAugust Time: 2017-10-25 09:37
Edited by WisdomAugust at 2017-10-25 09:40
Types of Scopes
Oscilloscopes can be classified as analog and digital types.
Analog Oscilloscopes
[attach]1741[/attach]
An analog oscilloscope works by applying the measured signal voltage directly to the vertical axis of an electron beam
that moves from left to right across the oscilloscope screen - usually a cathode-ray tube (CRT). The back side of the
screen is treated with luminous phosphor that glows wherever the electron beam hits it. The signal voltage deflects
the beam up and down proportionally as it moves horizontally across the display, tracing the waveform on the screen.
Analog oscilloscopes are characterised by the large screens used in traditional 'tune-up' machines and the smaller
scopes with the glowing green screens used in electronics. They are excellent tools, however in automotive use they
suffer from major drawbacks - the need for mains power, the greater difficulty in set-up and the absence of a storage
mode that allows the freezing of the on-screen image.
Author: WisdomAugust Time: 2017-10-26 08:35
Digital Oscilloscope
[attach]1744[/attach]
A digital oscilloscope uses an analog-to-digital converter (ADC) to convert the measured voltage into digital information.
It acquires the waveform as a series of samples, and stores these samples until it accumulates enough samples to
describe a waveform. It then re-assembles the waveform for display on the screen.
The digital approach means that the oscilloscope can display any frequency within its range with stability, brightness,
and clarity. It can also easily freeze the waveform, allowing it to be studied at leisure. Digital scopes can usually be
powered by batteries and use an LCD screen. All scope adaptors that are used with laptop PCs are digital.
Author: WisdomAugust Time: 2017-10-27 09:09
Edited by WisdomAugust at 2017-10-27 09:11
Scope Systems and Controls
An oscilloscope has three main controls, labelled Vertical, Horizontal, and Trigger.
You need to adjust these three basic settings to accommodate an incoming signal:
a) The attenuation (reduction) or amplification (increasing) of the signal - use the volts/div
(volts per on-screen division) control to adjust the height of the signal to the desired
measurement range.
b) The time base - use the sec/div (seconds per on-screen division) control to set the
amount of time per division represented horizontally across the screen.
c)The triggering of the oscilloscope - use the trigger level to stabilize a repeating signal,
or to trigger on a single event.
These adjustments sound more complex than they actually are: what you want to see
is a steady waveform that fits on the screen. The first point (a) simply fits the waveform
on the screen vertically, (b) sets the bottom axis so that the waveform repeats sufficiently
that you can recognise it, and (c) makes sure that the waveform is clearly depicted.
And as we said, some digital scopes have an 'auto' button that do all of these things for you!
Author: WisdomAugust Time: 2017-10-28 08:12
Edited by WisdomAugust at 2017-10-28 08:14
Scope Measurement
Voltage Measurements
[attach]1747[/attach]
The oscilloscope is primarily a voltage-measuring device. The most basic method of taking voltage measurements
is to count the number of divisions a waveform spans up the oscilloscope's vertical scale. Adjusting the volts/div control
signal to allow the signal to cover most of the screen vertically makes for the best voltage measurements. The more screen
area you use, the more accurately you can read from the screen. Then it's as simple as reading off how many divisions per
volt the scope is set to, and estimating on-screen how many divisions the waveform covers.
With AC signals (eg a sinewave from a speed sensor), you would normally look at the peak to peak voltage.
With a DC voltage, the whole line will be elevated from the zero point. Some scopes will do these calculations for you.
Author: WisdomAugust Time: 2017-10-30 08:21
Time and Frequency Measurements
You can make time measurements using the horizontal scale of the oscilloscope.
Time measurements include measuring the period and pulse width of pulses.
Remember that frequency is the reciprocal of the period, so once you know the
period, the frequency is one divided by the period. Like voltage measurements,
time measurements are more accurate when you adjust the portion of the signal
to be measured to cover a large area of the screen. Again, some scopes will do
these calculations for you.
Author: WisdomAugust Time: 2017-11-1 08:10
Edited by WisdomAugust at 2017-11-1 08:12
Pulse Width and Rise Time Measurements
In many applications, the details of a pulse's shape are important. Pulses can become distorted and cause a circuit to malfunction,
and the timing of pulses in a pulse train is often significant. Standard pulse measurements are pulse width and pulse rise time.
Rise time is the amount of time a pulse takes to go from a low to high voltage. By convention, the rise time is measured from 10%
to 90% of the full voltage of the pulse. Pulse width is the amount of time the pulse stays high. Some scopes will calculate and display
pulse width (measured in seconds) and also duty cycle (the proportion of time that a pulsetrain is high.)
Conclusion Using a scope gives you a window into a new world. No longer do you just see a static (or more often, flickering around!) voltages
coming out of a sensor or the ECU. Now you can see the shape of that signal - which is a whole lot more illuminating...
Author: WisdomAugust Time: 2017-11-6 08:54
Edited by WisdomAugust at 2017-11-6 08:55
Waveform diagnostics: Ignition diagnostics you will actually use
We are not going to get into the old stuff here that you’re already well acquainted with. The basic ignition system principles at work in a distributor
are no different from those that make a modern coil-on-plug (COP) ignition work. COP, even without a cap and rotor, still:
* charges and fire a coil with a switched circuit;
* needs good power and ground; and
* needs to know engine speed for ignition timing.
Being that pretty much everything has moved over to COP or waste-spark ignition, we are going to cover the essentials on these systems first.
Ignition coils and primary ignition
The one thing that every ignition system has in common is the ignition coil.
A coil is in effect the “middle” of the ignition system. Every component in the ignition system leading up into the coil is primary ignition. If you want to
get real technical, there is a metal coil with a carbon bar in the middle in the first part of the coil. Secondary ignition is every part after the coil. Again,
technically speaking there is a second set of winding, in the second half of the coil.
Author: WisdomAugust Time: 2017-11-7 08:50
Swapping coils and just looking at misfire counter on Mode 6 or checking for misfire DTCs is a common,
but less precise, practice. Personally, we sell the customer on all new ignition coils or threaten them with
diagnostic costs to pick out the bad ones. That seems to do the trick.
Every coil, no matter the vehicle, needs power. So anything that inhibits the coil getting power will
compromise its performance. Be sure to check for the following:
? Correct voltage — A voltage drop to the coil can make it ineffective.
? Good switching — If the “switch” wherever it’s location (points, ICM, D.I.S, PCM these days, etc.) contact
has high resistance, or if the ground connection is bad, power to the coil is reduced, weakening the spark.
Author: WisdomAugust Time: 2017-11-8 11:20
Edited by WisdomAugust at 2017-11-8 11:37
Secondary ignition
On old vehicles, after the ignition coil was an ignition rotor, distributor cap, spark plug wires and spark plugs. The ignition coil provided the high voltage power,
and this power was distributed and transferred to the plugs through the rotor, cap and wires. All of this is secondary ignition.
Modern ignition systems still have what we call “secondary,” but they use fewer parts.
*Waste-spark ignition gets rid of the distributor cap and just has spark plug wires and spark plugs.
[attach]1777[/attach]
This is what the internal construction of an ignition coil looks like.
*COP gets rid of everything but the plugs! As we can see above picture, the secondary boot and spring on these coils essentially connects right to the plugs,
making everything else unnecessary. The secondary has more windings than the primary. The windings increase the voltage, but decrease current. This voltage
increase enables power to jump the spark plug gap.
*NOTE: Replace ignition coil boots when doing tune-ups whenever possible, especially if they are on GMs or you see any evidence of arcing (white crust).
Author: WisdomAugust Time: 2017-11-9 13:20
Edited by WisdomAugust at 2017-11-9 13:23
Coil-on-plug ignition in detail
COP is here to stay until vehicles become all like diesels and ignite using compression. Because COPs do not use plug wires,
this reduces the amount of ignition parts and makes them better suited for high kilovolts (KV) demand during high engine loads.
With one coil per plug, a dead coil affects only one cylinder. Each coil has a two-pin connector. One pin receives system voltage
and the other is grounded to the PCM, allowing the coil to charge and discharge. This makes them very easy to diagnose via coil
swapping or the “comparison game” with the scope. As a side note, leaking coil boots should be replaced, not only to stop misfires
but also to protect the PCM.
Author: WisdomAugust Time: 2017-11-10 08:52
Edited by WisdomAugust at 2017-11-11 08:12
Testing COP system voltage
Unplug the coil and probe the hot side of the coil connector with your DMM. Watch the voltmeter as you turn the key ON,
or set the meter to volts DC in Min/Max mode so it can record the maximum voltage for you. Our meter in the photo above
has captured a 13.36 volt reading indicating that our circuit is intact. This is a good specification for Chrysler COP.
[attach]1786[/attach]
The arrow points to where we would put our meter’s positive probe.
We can simply put the other probe onto a ground.
Author: WisdomAugust Time: 2017-11-11 08:24
COP testers
There are several COP testers that give us valuable information such as firing KV and burn time without any backprobing.
We show a COP tester, which can make it easy to get an ignition waveform.
Waste-spark ignition in detail
A few stragglers (Subarus for example) still use waste-spark. Waste-spark ignitions all work the same. They fire a pair of
spark plugs directly connected to a single coil via ignition wires. Because they are connected right to the coil, both plugs in
a given pair fire simultaneously.
How does the engine run properly? Well, one cylinder is in its compression stroke while the other is in its exhaust stroke.
So, one plug fires during the compression stroke allowing the power stroke to subsequently take place. As for the cylinder
with the exhaust stroke, the plug fires but nothing happens. The spark is just wasted, hence the term “waste-spark.”
If you see one spark plug with normal wear and the other one wearing inside out don’t worry, that is normal. When diagnosing
these systems, just apply standard diagnostic principles, but use your common sense. Two cylinders misfiring that share the
same coil likely have an issue whose source stems to the coil.
Instead of a distributor, all new systems use the CKP or CMP sensors. The rpm signal from these sensors is sent to the PCM
through the ignition module. Using primarily engine speed, the PCM controls the primary circuit switching on/off.
Author: WisdomAugust Time: 2017-11-13 09:06
Waste-spark ignition waveforms
The required firing voltage for the spark plug on the power stroke should be higher than firing voltage
for the plug on the exhaust stroke. (In below picture, you’ll see ignition waveforms of a waste-spark system.)
[attach]1789[/attach]
Ignition waveforms of a typical waste-spark system.
Why do we care that waste-spark waveforms are smaller than regular ignition waveforms captured during the
combustion event? If waste-spark firing voltage ever equals power stroke firing voltage, look for an open plug wire
with an air gap greater than either plug gap. This open becomes the greatest gap and it forces coil energy to rush
through it. This need for increased voltage will push up the waveform to a level it should not be at.
Author: WisdomAugust Time: 2017-11-14 08:29
Edited by WisdomAugust at 2017-11-14 08:33
Real-world ignition tests
The following list of standard ignition tests is not as long as you might think. The reason? As we’ve already pointed out,
the fundamentals of ignition system operation are universal.
Here are common ignition tests that ought to be in your troubleshooting arsenal:
* available voltage test;
* secondary insulation tests;
* ignition coil primary voltage drop test; and
* low amp probe current ramping test.
Available voltage test
The available voltage test is a good test if it is performed properly. It tells us if the ignition system can generate enough
spark voltage to jump the spark plug gap.
To perform the test, you’ll need a dedicated spark tester that stresses the coil to output at least 40,000 volts. Do not use
any other spark tester, such as the one with a light or the old clip/no ground spark plug tester, it won’t place a high enough
demand on the ignition to truly test it.
1. Remove the plug wire and connect it to the spark tester.
2. Make sure the tester is properly grounded.
3. Crank the engine and look for a strong blue spark at the tester.
A strong blue spark tells you that everything leading up to the wire (including the coil) is good and that your problem lies
elsewhere. If the spark is any other color, you will want to test further up the secondary or even the primary side of ignition
to see where the power loss originates. (In below picture, you’ll see the available voltage test being conducted with a spark tester.)
[attach]1793[/attach]
The available voltage test being conducted with a spark tester.
Author: WisdomAugust Time: 2017-11-15 08:56
Insulation tests
Why do engines that idle with no misfire begin to misfire under load?
The main reason is that spark plugs require increasingly higher KV to fire when engine load increases.
Secondary insulation that can contain 10 KV at idle may leak when asked to contain 20 KV or more under load.
So how do you find a leaking plug boot, especially in engines where the plug and plug boot are out of sight inside
a tube in the valve cover? You can either eliminate the insulation leak altogether, or make it worse.
You can make the condition worse by wrapping the plug boot in aluminum foil and reinserting it. The foil makes
a more conductive path between the plug wire and metal tube. This should make a damaged plug boot leak at
lower KV and misfire at idle.
If you locate a likely suspect with the first test, verify that the boot is indeed a problem by wrapping it with high
quality electrical tape. Put the engine under load again and see if the misfire is gone.
In the real world you might decide to sell a tune-up or plan to replace COP boots the moment you see anything
fishy. But just in case the front office guy isn’t able to do that, these tests might be a real help to get him to sell the parts.
Author: WisdomAugust Time: 2017-11-16 08:17
Ignition coil primary voltage tests
Perfectly good ignition coils, plugs and wires are often replaced because the technician observed poor secondary spark.
However, low primary voltage might be the real culprit! Be sure to do a primary voltage drop test before condemning the coil!
1. Connect a meter between the battery positive post and the coil primary positive terminal.
2. Test KOEO and KOER. (If a no start, check engine cranking.)
3. Only 0.2 V is acceptable.
If the test results fail, you need to isolate where the voltage drop is, starting between the batter post and cable end, then
working your way up.
Don’t try this with a test light, because it won’t tell you anything useful. You need to find out if there is significant electrical
resistance, not whether there is any power there whatsoever.
Using the low amp probe on DIS
Not sure where to clamp on with your low amp probe to measure coil current in DIS?
Most DIS coil pack electrical connectors have a single power feed, regardless of the number of coils in the pack. Connect
here to get a good overall look of ignition coil amperage. To get a look at the spark plug pair, connect to the one coil primary
control wire leaving the coil pack.
Author: WisdomAugust Time: 2017-12-1 09:29
Interpreting ignition waveforms
There are two different ways to measure the spark firing event: hooking up an amp clamp on the primary side
of the ignition coil for current and backprobing the voltage primary side of the coil with a labscope lead to see
the waveform. In below picture, we can see how the amperage (above) and voltage (below) ignition waveforms
differ.
[attach]1860[/attach]
Here we test an insulation leak by making it worse by wrapping tin foil around the boot.
Author: WisdomAugust Time: 2017-12-4 08:15
Edited by WisdomAugust at 2017-12-4 08:18
The current waveform
1. The PCM (or points, or ICM, or etcetera) closes the ignition circuit and the coil begins to charge up.
That steady increase in amperage indicates that the coil is charging up.
2. The PCM opens the circuit just when amperage reaches its peak, causing current to plummet.
Instantly, voltage skyrockets allowing spark at a low current to jump the gap.
This current waveform shows a lower than normal rise and less of an angle. The coil is obviously defective,
notice the burn in the circle?
Following picture shows a real-world example that helps us understand the difference between a good and
bad ignition waveform.
[attach]1861[/attach]
This real-world example helps us understand the difference between a good and bad ignition waveform.
Author: WisdomAugust Time: 2017-12-5 15:38
Edited by WisdomAugust at 2017-12-5 15:43
The voltage waveform
First, let’s begin with a good overview of what makes up an ignition waveform.
[attach]1862[/attach]
Different parts of an ignition waveform.
1. The switch internal to the PCM (or ICM/points) closes. Current rushes into the coil
and begins to build, which is why voltage drops close to ground and essentially remains
there until the firing spark.
2. The coil is now saturated with electricity, as indicated by the jump in voltage. The
coil is no longer charging up thanks to the ICM/PCM.
3. The PCM switch opens, unleashing all the built-up current. Amps drop like a rock
and voltage skyrockets.
4. The spark line indicates the length of the spark event at the plug.
5. When not enough power is left for the spark, remaining power is rung out and the event
begins all over again.
Author: WisdomAugust Time: 2017-12-6 08:35
Edited by WisdomAugust at 2017-12-6 08:37
To understand the voltage waveform, you need to isolate each part of it to know what’s going on.
1. Firing voltage is the voltage in KV required to jump the largest single gap in the secondary (most
likely the spark plug gap). The gap between the rotor and distributor cap sometimes may be larger,
and this will affect what you see on your waveform.
[attach]1863[/attach]
The firing voltage section of the waveform.
Author: WisdomAugust Time: 2017-12-7 08:08
Edited by WisdomAugust at 2017-12-8 08:26
Expect spark plugs with plug gaps of .045-.060 inch to require 8 to 12 KV to jump the gap at no-load idle.
Sometimes an issue with weak spark, incorrect spark timing, fuel supply/delivery, low engine compression,
or something else that can cause a misfire can affect firing KV.
In fact, the waveform below is an example of how we can pick out an obvious misfire simply by looking at
ignition voltage.
[attach]1865[/attach]
Just by looking at primary voltage, we can quickly identify the problematic/misfiring cylinder.
Something is definitely making ignition in that cylinder work harder than it needs to!
Author: WisdomAugust Time: 2017-12-8 08:25
Edited by WisdomAugust at 2017-12-8 08:29
2. Spark voltage is the voltage in KV required to maintain the spark across the plug gap for the period of time
required to ignite the gas.
If firing voltage is higher than 2 or 3 KV, this decreases the duration of the spark, known as firing time. Firing
time should be about 1 or 2 mS.
[attach]1866[/attach]
Here we see the spark voltage part of the ignition waveform pattern.
Notes:
*Shorter spark times often indicate a weak ignition coil.
*In times where spark time is short and firing voltage is a typically high, this indicates that something is forcing
the ignition to expend all its energy on the initial spark, leaving nothing left for its duration.
* The slight upward spike in the end of the spark line is normal.
* Lean systems spike up right after the firing spike.
Author: WisdomAugust Time: 2017-12-9 08:04
Edited by WisdomAugust at 2017-12-9 08:06
3. Oscillations occur when the spark has ended because the energy necessary for the spark has been extended.
There is still some energy left in the ignition coil, but not enough to continue the spark event. So, the remaining
power oscillates up and down, effectively ringing itself out.
[attach]1867[/attach]
Oscillations are easily detected in most ignition waveforms.
Notes:
* Sometimes, some ignition systems have one coil oscillation.
* A fouled spark plug has neither a definitive spark line nor oscillations.
Author: WisdomAugust Time: 2017-12-11 08:21
Edited by WisdomAugust at 2017-12-11 08:25
Why look at ignition waveforms?
Spark line voltage, shape and time tell us more about the spark than the firing voltage KV does.
Because of this, try stacking (Raster) the waveforms on your scope. It will make comparing the
spark line much easier to do. Take a look at the spark line on number 6 cylinder that had a
compression problem.
[attach]1871[/attach]
Ignition waveforms on the Scope that had a compression problem.
It’s tough when using labscopes. When are we being too critical and when are we not looking close
enough? Sometimes we only know in retrospect. Here the firing time reflects the cylinder with the
problem, but the firing lines of all the cylinders are hardly identical. That’s why we need many tools
in our boxes to pinpoint vehicle problems, ignition diagnostics is just one of them.
Author: WisdomAugust Time: 2017-12-12 08:30
Edited by WisdomAugust at 2017-12-12 08:37
Comparing voltage and current in primary waveforms
Comparing voltage and current waveforms is a great way to locate the problem and the reason for the problem.
The ICM or PCM is responsible for switching on/off the primary circuit. When the switch opens, it must open quickly
to properly create spark. Slow switching reduces secondary spark intensity. Have trouble visualizing this? Take a look
at how the current drops instantly when the switch opens compared to the opposite in the waveform below.
[attach]1896[/attach]
[attach]1897[/attach]
Why does the spark event look so bad in the below waveform? The current waveform tells us here. The amperage
does not drop straight down during the firing event. It instead steeply slopes down. This means that the switch internal
to the PCM/ICM is opening too slow. We just diagnosed a bad module.
In the pictures we can diagnose a bad computer by looking at voltage waveforms against amperage waveforms.
Author: WisdomAugust Time: 2017-12-13 14:09
Edited by WisdomAugust at 2017-12-13 14:12
Secondary ignition waveform analysis
Now, you won’t be needing to scope too much secondary ignition anymore, but some vehicles still use ignition wires.
And when the mood strikes you to scope secondary ignition, keep in mind that secondary waveforms look a lot like
primary waveforms.
[attach]1902[/attach]
Can you tell the difference between the secondary and primary waveform?
The reason this is so is because primary ignition directly affects secondary. In the below waveform Channel A
is Primary Ignition and Channel B is Secondary Ignition. They both look very similar except for the dwell section.
For this reason if an ignition primary originates on the primary, it will askew your secondary waveforms. Be sure
to scope secondary ignition AFTER confirming primary ignition is good.
This is how secondary waveforms should look.
1. The coil begins charging up full of current. The oscillations are magnetic interference from a working ignition coil.
2. During the dwell period, voltage builds very slowly.
3. The ignition coil unleashes all of its current into the secondary side of that same coil. Voltage skyrockets.
Instantaneously the spark jumps the spark plug gap.
4. Spark line should be relatively high in voltage. Its duration is the firing time.
5. Oscillations happen when there is not enough power to continue the spark and any remaining power is squeezed out.
Author: WisdomAugust Time: 2017-12-14 16:08
Edited by WisdomAugust at 2017-12-14 16:19
Real world secondary ignition diagnostic tips
* High voltage at point 3 in below picture is usually the result of a wide plug gap (or some other gap on
the secondary side depending upon the system) or high cylinder pressure. This lessens firing time (point 4).
[attach]1910[/attach]
Here we illustrate the steps of a secondary ignition waveform.
* A voltage drop on the secondary side will not affect firing KV, but will increase the spark line (4) and lessen
firing time.
* With COP you probably won’t be scoping the secondary. This is a tip we covered in part one of this article.
If you really want to, connect ignition wires between the coil and the plugs if possible and measure the old
fashioned way. In the real world just play the comparison game. You have at least four coils to choose from.
Chances are you can just scope the primary and pick out the coil that’s bad. Simply change the coil along
with the plug, or better yet sell the whole tune-up after that.
Author: WisdomAugust Time: 2017-12-15 09:28
Edited by WisdomAugust at 2017-12-15 09:30
Secondary waveform comparison game
See below picture. We have our ignition scope hooked up to secondary ignition,
using a parade pattern presentation.
[attach]1911[/attach]
In this example, cylinder number 4 presents an obvious misfiring.
Assume the vehicle has a misfire. Which cylinder is misfiring? Obviously cylinder 4! As you
can see, the comparison game is an effective diagnostic method.
Author: WisdomAugust Time: 2018-1-2 11:04
Sometimes you won’t be able to pick up an issue with the secondary ignition under normal conditions
(such as misfiring at high speeds).
So, a snap throttle test places more demand on the secondary ignition, making the comparison game
easier to play. As you can see below, snapping the throttle can accentuate a misfiring cylinder so you
can catch it.
[attach]1947[/attach]
Snapping the throttle can accentuate a misfiring cylinder so you can catch it.
In cylinder 1 it required more voltage to fire the plug, noticeably shortening the spark duration.
Author: WisdomAugust Time: 2018-1-8 14:22
Application of Secondary Ignition Waveform to Automobile Fault Diagnosis
Ignition waveform reflects the relationship between the variation of primary, secondary electical current and voltage of ignition coil
and the time or crankshaft turn angle of engine during operation of the engine ignition system, which is displayed on an oscilloscope
and can show working mode of the ignition system in real time.
Secondary ignition waveform analysis is a common method of fault diagnosis of modern vehicles.
Let’s analyze the standard waveforms and fault waveform of ignition system and use a typical fault waveform example to illustrate
how to use the secondary ignition waveform for automobile fault diagnosis.
Author: WisdomAugust Time: 2018-1-9 14:18
1 Secondary standard waveform analysis
Secondary coil of the secondary ignition waveform is shown in figure 1, each point analysis is as follows:
[attach]1951[/attach]
Secondary Ignition Standard Waveform
Point a: Primary coil turn on (The current increasing is slow when primary coil turn on, thus the electromotive
force generated from secondary coil is slow as well, and its direction is opposite.)
Point b: Primary coil current reached the point of saturation (i.e. turn on the primary coil, when current rised upto
the point of constant current value, the constant current function of ignition controller start to work.
Section a - b: The primary coil switch-on, current increases until the ignition controller starts the constant current
control process (build the magnetic field energy).
Author: WisdomAugust Time: 2018-1-10 08:51
Section a - b: The primary coil switch-on, current increases until the ignition controller starts the constant current control
process (build the magnetic field energy).
Point c: The moment of primary coil power-off (ignition controller controls primary coil power-off and starts to ignition).
Section b - c: constant current control section (the holding constant current section when primary coil current rose to the
ignition controller constant current ). Constant current: indicates the ignition primary coil charging current rises to a certain
amperage and stabilizes the charging to coil.
Author: WisdomAugust Time: 2018-1-11 10:52
Section a - c: closing angle (primary coil energization time from primary coil on to the ignition). Generally, 4 cylinders engine
closing angle is 45% - 60%, i.e. calculated according to the camshaft angle is 90 x (45 ~ 60)%; and calculated according to
the crank angle is 180 x (45 ~ 60)%, which means that the closing angle time is one cylinder complete a work cycle, the
camshaft angle is 90 degrees, and the crankshaft rotation angle is 180 degrees, and in the entire working cycle, the ratio
is 45% to 60% of the angle. But 6-cylinder engine closing angle is 60% - 70%.
Author: WisdomAugust Time: 2018-1-12 13:39
Point d: Breakdown high voltage generated by the secondary coil at the moment of primary power failure
breaks down the highest voltage point of the spark plug gap, immediately dropping once the spark plug
gap has been broken. The breakdown voltage is affected by many factors, such as spark plug gap, spark
plug electrode shape, mixture concentration, cylinder pressure, cylinder compression temperature and
so on.
The larger the spark plug electrode gap, the sharper the electrode shape, the higher the breakdown voltage
and the greater ignition energy required. Mixture is too thick, because HC and air molecules are compressed
and squeeze intensive, high pressure to make it more difficult for positive and negative electron separation,
the need for greater voltage to make it ionized to form an electron flow spark. Mixture is too thin, HC and air
molecules are relatively thin, the molecules can not be ionized at the same time, so that the higher the ionization
voltage can penetrate the slender gap. The higher the temperature, the more active molecules, ionization easier,
the required breakdown voltage is low, on the contrary the required voltage is high. Only moderate gas mixture, oil
and gas molecules are evenly distributed, the electrode generates electron flow is relatively easy, the breakdown
voltage at this time is the standard voltage.
Author: WisdomAugust Time: 2018-1-15 08:43
Point e: the starting point of spark formation (i.e. the moment when the high voltage breaks down the gap of the
spark plug to form the electron current, the conversion of thermal energy started).
Section c - f: capacitor discharge section (equivalent to a large capacitor discharge, spark formation process,
that is, the formation of electron flow breakdown ionization process).
Point g: the end point of spark (i.e. the lowest energy point of the magnetic energy conversion last until cannot
keep the electron current when breakdown form the electron current ).
Author: WisdomAugust Time: 2018-1-16 08:28
Section f - g: the duration of the spark, also known as the burning line, that is, the duration of the electron current after
the breakdown of electrode. The voltage is the spark burning voltage, is the voltage to maintain the spark transfer. Generally,
it’s 1/ 4 of the breakdown voltage. This section also called inductance discharge section. This section should be relatively flat,
clean and non-abnormal waveforms.
Section h - i: winding coil normal attenuation oscillation part: usually there are more than 3 oscillation waveforms, and standard
is 5 to 6 waveforms. That is after the magnetic energy conversion electric energy can not maintain the spark conduction, the
magnetic energy of the primary coil and the secondary coil decay and disappear from each other. If the attenuation wave is
too little, the performance of the coil is degraded.
Author: WisdomAugust Time: 2018-2-1 13:05
Secondary coil waveform analysis principle: When igniting, the secondary coil generates a high voltage,
when the voltage gradually up to a certain value, the spark plug spark (In the test, the spark energy show
a blue-white flame, and last 1. 5 ~ 2. 4 ms (distributor system). In the non-distributor ignition system,
the standard spark time must be above 0. 8 ~ 1. 8ms. Such a flame in the cylinder owns high energy,
fast propagation, the rapid combustion within the cylinder Full, explosive pressure, engine power output
high), this voltage is the ignition voltage. Then the voltage drops rapidly to another voltage value and
maintain a period of time, the voltage is the combustion voltage, the combustion time is the voltage is
maintained at the combustion voltage value of the time. At the end of the burning time, the energy in the
ignition coil is basically exhausted, and the residual energy forms damped oscillation on the coil.
The number of oscillation waves is required to be more than 3 (standard 5 to 6).
Author: WisdomAugust Time: 2018-2-3 11:18
Secondary coil waveform analysis principle: When the ignition, the secondary coil produces a high voltage,
when the voltage gradually increases to a certain value, the spark plug spark (test spark energy performance
for the blue-white flame, and can continue 1. 5 ~ 2.4 ms (distributor system), in the absence of distributor
ignition system, the standard spark time must be 0. 8 ~ 1. 8ms or more.
This flame in the cylinder of high energy, fast propagation, the rapid combustion of the cylinder full, explosive
pressure, the engine power output high), this voltage is the ignition voltage. Then the voltage drops rapidly to
another voltage value and maintain a period of time, the voltage is the combustion voltage, the combustion
time is the voltage is maintained at the combustion voltage value of the time. At the end of the burning time,
the energy in the ignition coil is basically exhausted, and the residual energy forms damped oscillation on the
coil. The number of oscillation waves is required to be more than 3 (standard 5 to 6).
Ideally, the secondary waveform is very stable, indicating that the voltage at each ignition firing is the same.
The graphics of each cylinder should be roughly the same. However, the actual situation is not ideal, the graphics
will always have larger or smaller jitter, such as ignition or breakdown voltage fluctuated, burning time may vary,
these do not necessarily indicate that the engine is faulty. This third Gao Lu and: secondary ignition waveform in
the application of fault diagnosis 7 will require our accumulated experience, combined with other test data
comprehensive analysis.
Author: WisdomAugust Time: 2018-2-5 16:14
2 secondary ignition waveform fault point analysis
The measured engine ignition waveform display, the first should be with the standard wave
Shape control. If the measured ignition waveform exactly the same as the standard waveform, said
Ming fire system technical condition is good; if the measured waveform is abnormal, that
Ignition system or other system fault, should be different according to the ignition waveform
Failure to reflect the area, diagnosed the cause of the malfunction.
2. 1 ignition coil charging part
Observe that the ignition coil remains relatively constant at the beginning of charging
The falling edge of the waveform indicates the consistent closing angle and ignition of each cylinder
When accurate, if not coincidental, ultra-poor too much to prove that the super-poor cylinder ignition line
Circle controller bad ground or performance degradation. If the falling edge is a slope,
Then the controller power tube performance degradation or poor grounding; view
Whether the closed angle of each cylinder can be consistent; check the closing angle of the large
Small whether the engine operating conditions the size of the correct adjustment.
Author: WisdomAugust Time: 2018-2-5 16:15
2 Secondary ignition waveform fault point analysis
The measured engine ignition waveform display, the first should be with the standard wave
Shape control. If the measured ignition waveform exactly the same as the standard waveform, said
Ming fire system technical condition is good; if the measured waveform is abnormal, that
Ignition system or other system fault, should be different according to the ignition waveform
Failure to reflect the area, diagnosed the cause of the malfunction.
2. 1 Ignition coil charging part
Observe that the ignition coil remains relatively constant at the beginning of charging
The falling edge of the waveform indicates the consistent closing angle and ignition of each cylinder
When accurate, if not coincidental, ultra-poor too much to prove that the super-poor cylinder ignition line
Circle controller bad ground or performance degradation. If the falling edge is a slope,
Then the controller power tube performance degradation or poor grounding; view
Whether the closed angle of each cylinder can be consistent; check the closing angle of the large
Small whether the engine operating conditions the size of the correct adjustment.
Author: WisdomAugust Time: 2018-2-6 14:27
2.2 secondary ignition voltage analysis
Check whether the breakdown voltage changes to meet the needs of the engine operating conditions change;
Check the breakdown voltage in the cylinder can be consistent between the various; through the breakdown
voltage level to determine the ignition system fault.
Breakdown voltage level with the cylinder pressure, the concentration and pressure of the mixture, the ignition
system secondary circuit resistance. The following is divided into four cases for failure analysis and judgment:
(1) If the ignition voltage of each cylinder are too high, exceeding the upper limit of the specified value, it may
be too mixed or too thick mixture, distributor central high-voltage line end is not inserted in the end or distributor
cover dirty, Distributor cap socket electrode gap is too large or each cylinder spark plug gap is too large and
other reasons.
Author: WisdomAugust Time: 2018-2-7 11:28
(2) If the individual cylinder ignition voltage is too high, it may be the end of the cylinder pressure line is not inserted in the end,
the distributor cover dirty dirty or distributor cap jack electrode and sub-fire is not the same heart, The high-pressure cylinder
jack electrode gap is too large or the cylinder spark plug gap is too large, spark plug damage caused by other reasons.
(3) If the ignition voltage of each cylinder is too low, lower than the lower limit, it may be spark plug gap of each cylinder is too
small, the spark plug electrode oil, ignition coil performance is poor, the battery voltage is insufficient or the capacitor capacity
and other causes.
(4) If the individual cylinder ignition pressure is too low, it may be the cylinder spark plug clearance is too small, spark plug
electrode oil or spark plug insulation properties caused by poor and other reasons.
Author: WisdomAugust Time: 2018-2-8 15:18
2.3 Combustion line analysis
Observing sparks or burning line should be very clean, no excessive clutter on the combustion line, excessive clutter indicates poor cylinder ignition,
The reasons: premature ignition, injector damage, spark plug dirty or other reasons.
2. 3. 1 Burning time test conditions
(1) The engine running up to normal operating temperature;
(2) Adjust the engine speed to 2000r / m in.
Normal standard spark time 1. 5 ~ 2. 4ms (distributor system ), in the absence of distributor ignition system, the standard spark time must be 8 ~ 1. 8m s or more.
Author: WisdomAugust Time: 2018-2-9 09:19
(1) Spark time is less than 0. 8m s reasons:
a. High voltage line resistance is too large;
b. Spark plug gap is too large;
c. Sub-disc and sub-fire head gap is too large;
d. Mixed gas too thin;
e. Spark plug temperature is too cold;
f. Ignition timing is too slow;
g. Cylinder pressure is too high;
h. Valve spring is too weak.
(2) Sparking time is higher than 2. 4m s reasons:
a. High voltage line resistance is too small;
b. Mixing ratio too thick;
c. Spark plug gap is too small;
d. Cylinder pressure is too low;
e. Spark plug temperature is too hot;
f. Engine oil consumption;
g. Ignition timing too early;
h. The valve clearance is too small.
Author: WisdomAugust Time: 2018-2-11 10:56
3 secondary ignition fault waveform analysis
It should be noted that a lot of fault performance in the waveform of each cylinder, but also some fault performance
in a single cylinder waveform.
Here are some typical fault waveforms.
(1) If the secondary waveform is inverted (the waveform of each cylinder is the same), as shown in Figure 2, the ignition
primary line is reversed.
[attach]2022[/attach]
Figure 2 a line reverse
Author: WisdomAugust Time: 2018-2-12 08:20
(2) If the secondary waveform breakdown voltage is too high, and there is no good discharge process,
the spark of the relatively steep stage, as shown in Figure 3, indicating that the secondary circuit
resistance is too large, may be secondary circuit open circuit, poor contact or spark plug gap, sub-fire
head and distributor gap is too large and other causes. This failure may occur in every cylinder waveform,
may also appear in a cylinder waveform.
[attach]2023[/attach]
Figure 3 secondary line resistance is too large
Author: WisdomAugust Time: 2018-2-26 08:34
(3) If the spark voltage of the ignition waveform fluctuates, as shown in Fig. 4, it indicates that the injector
of the EFI system is working poorly, causing the concentration of the combustible mixture to fluctuate.
This failure may occur in every cylinder waveform, may also appear in a cylinder waveform.
[attach]2033[/attach]
Figure 4 EFI system injector work poorly
Author: WisdomAugust Time: 2018-2-27 08:18
(4) If the ignition voltage of the ignition waveform is low, as shown in FIG. 5, it may be caused by the rich
mixture of the combustible mixture or the spark plug leakage. When the combustible mixture is too rich,
the ionization degree is small and the breakdown voltage is high at the initial stage of ignition, but the
ionization degree is increased during the sustaining spark and the spark voltage is reduced (the waveform
of each cylinder is the same). When the spark plug leakage, the spark voltage is also reduced (a cylinder
waveform).
[attach]2035[/attach]
Figure 5 Combustible mixture is too rich or spark plug leakage
Author: Rose Time: 2018-2-28 08:11
(5) If the secondary juxtaposed wave from time to time there are beating phenomenon (each cylinder
waveform is the case). Shown in Figure 6, indicating the secondary circuit intermittent power outages.
[attach]2037[/attach]
Figure 6 secondary circuit intermittent power outages
Author: Rose Time: 2018-3-1 15:54
(6) If the breakdown voltage of secondary parallel wave less than 5kV (the waveforms of each cylinder
are the same), as shown in Figure 7, indicates that the secondary coil is leakage.
[attach]2045[/attach]
Figure 7 secondary coil leakage
Author: Rose Time: 2018-3-2 11:58
Edited by Rose at 2018-3-2 13:31
Example analysisA Dodge McLaren (3. 3L), the engine speed at 800 ~ 3000r / m in, poor acceleration. After a preliminary
inspection of oil, circuit, found no abnormalities.
When the oscilloscope is used to detect the engine, the secondary waveform shown in FIG. 8 is obtained.
In the secondary ignition waveform test, an abnormal waveform appeared in each of the first, second, fourth
and fifth cylinders, that is, before the breakdown voltage, a small abnormal peak appeared. The normal
waveform is that when the ignition power transistor is suddenly disconnected from the closed state, the
magnetic flux decreases rapidly as the primary current drops to zero, so that the voltage generated by
the secondary coil rises sharply and penetrates the spark gap before the maximum value The voltage is
the breakdown voltage.
[attach]2047[/attach]
Figure 8 single cylinder secondary ignition waveform
Author: Rose Time: 2018-3-3 08:46
In Figure 8, it can be seen that before the breakdown voltage, a peak voltage of about 4 kV is generated
in the secondary circuit. The generation of this voltage, ignition coil secondary circuit should be due to
turn-to-turn short circuit.
In the secondary voltage generation process, due to local short circuit, so that part of the ignition energy
loss, and can not meet the acceleration required energy requirements. Causing the engine to work normally
at idling conditions and not working well during acceleration. After replacing the new ignition coil, acceleration
performance returned to normal.
5 Summary
The firing waveform is a window through which we can see what is happening in the combustion chamber.
The use of oscilloscope to observe the ignition waveform is one of the important methods to achieve rapid
detection and diagnosis. Among them, especially the observation of secondary waveforms, it is considered
to be a very effective comprehensive test.
If the measured secondary waveform of the engine is no problem, indicating that the ignition system, fuel
supply system and cylinder sealing are no problem.
Author: Rose Time: 2018-3-5 08:32
Vehicle Diagnostics with Oscilloscope
What is the oscilloscope?
Unlike the voltmeter, with an oscilloscope you can not only see the mean values of the voltage in
the circuits measured, but also the change and shape of that voltage through time.
All oscilloscopes have screens on which the waveform is shown. The screen can be a cathoderay
tube type, a liquid crystal display (LCD) or in the form of a computer program. The typical
oscilloscope screen is divided into equal spaces (divisions) which allow to visually interpreting
the parameters of the signal.
The graphics shown on the monitor are called waveforms. Usually oscilloscopes show only
waveforms of the voltage. This form of visualization shows the change of voltage through time.
The divisions marked on the horizontal(x) axis allow for the time parameters to be measured,
and the vertical(y) axis allow for the voltage values to be measured.
Author: Rose Time: 2018-3-6 08:17
What purposes have oscilloscopes in auto diagnostics?
The oscilloscope helps us find the problem quicker and easier. Often the problem hasn’t recorded
an error code (DTC) in the corresponding ECU, a DTC that can be read with a code reader.
Usually a DTC is recorded when there is a broken cable or a cable has short circuited to a
positive or negative supply. But when a detector or a mechanism has stopped working in some
mid position, there is no error recorded. In this case, as when you need to find the reason that
caused an error to be recorded – the automobile oscilloscope is your most needed instrument.
With the increase of sensors, actuators and wiring diagrams built in the modern automobiles, the
automobile oscilloscope is an instrument which diagnoses irregularities in the automobile faster
and easier. The oscilloscope is a irreplaceable tool, when you have to observe output signals
from inductive sensors, whose output signals form a impulse sequence, slow-changing analog
signals, primary and secondary ignition circuits, intake manifold absolute pressure, starter
current waveforms, charging currents and etc.
Author: Rose Time: 2018-3-7 10:42
What types of oscilloscopes are there?
Analog oscilloscope
The ones with a cathode-ray tube screens. They show detailed graphics, and can usually show
high frequencies, but are not suited for observing short processes repeated through a long time
interval or relatively slow processes like the ones in an automobile.
Digital storage oscilloscope
The observed result from the digital storage oscilloscope is almost identical to the analog, but the
signal shown on the DSO can be “frozen still” on the screen, saved on the PC’s hard drive, and
used later, or printed. Further more only the current “screen” shown on the monitor can be saved,
and a sequence of many screens can later be opened and observed through time as an animation.
Any screen saved in the working fail can be printed.
There are two kinds of digital oscilloscopes: independent which are external device, and PC
oscilloscopes. The PC-based oscilloscopes are a new type of "oscilloscope" that consists of a
specialized signal acquisition board, which can be an external USB or Parallel port device, or an
internal add-on PCI or ISA card.
One, dual and multiple-trace oscilloscopes
Depending on the number of measuring inputs, both analog and digital oscilloscopes can be
divided into 3 types: one-trace, dual-trace and multiple-trace oscilloscopes.
Universal and specialized oscilloscopes
Depending on their purpose oscilloscopes are divided into 2 groups – universal and specialized.
In automobile repair, an ignition analyzer is used to show the spark waveforms for each cylinder.
In this way the specialized automobile oscilloscopes are also used for testing injectors, ABS, O2
sensor, quick compression tests, fuel pump, CAN Bus and much more. The Motortester is a
specialized automobile oscilloscope.
Author: Rose Time: 2018-3-8 08:31
What’s the universal oscilloscope?
The universal oscilloscope is an electronic measuring device used only for observing electrical
voltage through time. The screen of the oscilloscope shows the changes in one or more input
signals over time in an X-Y display, allowing for the amplitude and shape of the voltage to be
accounted, as well as making phase and frequency measurements of the signal.
In order for the oscilloscope to observe other physical parameters, as well as observing voltages
outside its original ranges different types of additional attachments and transformers that convert
the given input into voltage are used.
Author: Rose Time: 2018-3-9 09:31
What is the difference between a motortester and a lab scope?
The motortester is one kind of specialized oscilloscope used for auto diagnostics.
The main difference between a motortester and a universal oscilloscope is that the motortester is
capable of visualizing short-timed processes like the ignition spark process. This process is
exceptionally fast, and the period of repeat of the ignition of sparks in time is many times greater
than the time the spark itself exists. This is easily observable when testing the engine in idle
speed, when the majority of the measurements are conducted.
For example: if we observe the ignition cycle of a 4 cylinder gasoline engine, and an ignition
spark that lasts around 2ms, at 800 RPM, the time period between sparks on a single cylinder
would be 150ms. What this means is that the ‘length’ of the spark would account for around 2%
of the actual work cycle, and therefore the burning of the sparks will be seen as very thin lines on
the screen of the oscilloscope, and no information about the phases of the ignition would be seen.
Because of this many diagnostics are forced to increase the RPM of the engine thus shortening
the ignition cycle thus ‘saturating’ the waveform of the cycle.
The motortester shows all the cylinders simultaneously, and allows for detailed observation of
the time period that includes: dwell period, drilling voltage, burn time and turbulence of voltage.
Most motortesters can show the cylinders graphs next to each other, or under one another,
excluding the long time periods between sparks, this method is also known as “parade”.
Another distinctive feature of the motortester is that it can show its time divisions on its
horizontal (x) axis in milliseconds as well as in degrees – up to 720 degrees.
Author: WisdomAugust Time: 2018-3-12 11:35
Features that allow PC-based oscilloscopes to be used in auto diagnostics.
Lower cost than a stand-alone oscilloscope, assuming the user already owns a PC.
Easy exporting of data to standard PC software such as spreadsheets and word processors
The software of the device can be directly installed on a PC and upgraded via CD or directly
download from the Internet without having to send the device back to its manufacturer.
Use of the PC's disc storage functions, which cost a lot extra when added to a self-contained
oscilloscope.
PCs typically have large high-resolution color displays which can be easier to read than the
smaller displays found on conventional scopes. Color can be utilized to differentiate waveforms.
PC-based USB oscilloscope get their power supply from a USB port, so no external source is
required.
The USB oscilloscope as any other USB device can be turned on/off without having to turn
off/on the computer.
Author: WisdomAugust Time: 2018-3-13 08:11
How many input channels are needed when conducting measurements in auto diagnostics?
When observing signals from sensors, valves, primary ignition chain, secondary ignition chain
etc. no more than one channel is needed. The first kinds of motortesters, which were analog,
needed more than one channel in order to show uniform signals simultaneously on the screen, so
they could be compared with each other. But whit PS based DSO’s this became unnecessary
because a standard waveform can be saved on the PC’s hard drive and opened at any time for
comparison with the currently observed.
Two channels are needed when the sequence in time between 2 signals has to be measured and
how many milliseconds are between them. In other words the second channel is used when the
phase difference between the 2 signals has to be observed and measured. An example for such a
measurement is when simultaneously observing signals from the Crankshaft Position Sensor and
the Camshaft Position Sensor.
Using more than 2 channels is more convenient in some cases but pointless from a functional
point of view.
Author: WisdomAugust Time: 2018-3-14 11:54
Where can scope waveforms used for comparison be found?
Most programs that contain automobile technical information have sections whose headlines
have “waveform”, “pattern” and “trace” in them. In other words these sections contain sets of
standard waveforms. Such programs are Autodata, Vivid Workshop, and many others that
contain technical information about automobiles. When looking at a “waveform” on the screen
you must not forget that this is just an ordinary coordinate system like the one everyone has
learned about at school. Like any coordinate system it has a horizontal (x) axis and a vertical (y)
axis. The vertical axis (height) represents voltage, and the horizontal (width) represents time.
The scale of both axes can be changed.
| Welcome to Electronic Engineer Discuss (https://www.eediscuss.com/) |
Powered by Discuz! X3.2 |