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Using Oscilloscopes on Vehicles

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 Author| Post time 2018-2-6 14:27:43 | Show all posts
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.


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 Author| Post time 2018-2-7 11:28:07 | Show all posts
(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.


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 Author| Post time 2018-2-8 15:18:43 | Show all posts
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.


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 Author| Post time 2018-2-9 09:19:22 | Show all posts
(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.


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 Author| Post time 2018-2-11 10:56:09 | Show all posts
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.









Figure 2 a line reverse


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 Author| Post time 2018-2-12 08:20:28 | Show all posts
(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.







Figure 3 secondary line resistance is too large


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 Author| Post time 2018-2-26 08:34:04 | Show all posts
(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.




Figure 4 EFI system injector work poorly



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 Author| Post time 2018-2-27 08:18:15 | Show all posts
(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).







Figure 5 Combustible mixture is too rich or spark plug leakage


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 Author| Post time 2018-3-12 11:35:15 | Show all posts
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.  






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 Author| Post time 2018-3-13 08:11:45 | Show all posts
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.  








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