Using Oscilloscopes on Vehicles

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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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(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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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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(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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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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(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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(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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(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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(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.





Figure 6 secondary circuit intermittent power outages

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(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.




Figure 7 secondary coil leakage