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Author: WisdomAugust

Using Oscilloscopes on Vehicles

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 Author| Post time 2017-11-10 08:52:50 | Show all posts
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.



The arrow points to where we would put our meter’s positive probe.
We can simply put the other probe onto a ground.




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 Author| Post time 2017-11-11 08:24:43 | Show all posts
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.

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 Author| Post time 2017-11-13 09:06:42 | Show all posts
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.)
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.



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 Author| Post time 2017-11-14 08:29:27 | Show all posts
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.)

The available voltage test being conducted with a spark tester.


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 Author| Post time 2017-11-15 08:56:19 | Show all posts
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.

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 Author| Post time 2017-11-16 08:17:11 | Show all posts
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.

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 Author| Post time 2017-12-1 09:29:41 | Show all posts
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.



Here we test an insulation leak by making it worse by wrapping tin foil around the boot.



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 Author| Post time 2017-12-4 08:15:46 | Show all posts
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.




This real-world example helps us understand the difference between a good and bad ignition waveform.


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 Author| Post time 2017-12-5 15:38:31 | Show all posts
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.

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.


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 Author| Post time 2017-12-6 08:35:16 | Show all posts
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.





The firing voltage section of the waveform.


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