On the ASE A8 test you will also need a understanding of the ASE A8 Ignition System operation and Secondary waveform analysis.
A wave analysis can help the technician make a diagnostic decision in three essential areas:
Electrical resistance: all air gaps, from rotor/cap too spark plug and any resistance in between.
Compression Resistance: mechanical integrity of the engine
Combustion Resistance: air/fuel ratio problems
All will effect secondary ignition patterns
Understanding ASE A8 IGNITION SYSTEM RESISTANCE
To check for secondary firing KV uniformity between cylinders (there should be no more than 20% difference between cylinders), you should note the firing voltage needed to overcome all the secondary resistance. Using the the display/parade parade pattern each technician should have mental picture what the firing voltage should look like.
Also remember if the firing voltage is within 20% of each other it doesn’t always means nothings wrong, remember the scope only shows the widest gap in the circuit.
In this case it’s better to put he vehicle under a load (in drive holding the brake, while giving the vehicle gas) and watch the secondary ignition to better diagnose the problem, watch the firing lines and spark lines to help find the misfiring cylinder.
Here are three popular spark plug gaps and a typical firing voltage:
.035 spark plug gap would show about 6-8kv (Kilovolts)
.045 spark plug gap would show about 8-10kv (Kilovolts)
.060 spark plug gap would show about 10 – 12kv (Kilovolts)
Now remember these are a rule of thumb, nothing concrete but if you see five cylinders firing at 10kv and number 6 firing with a large firing line with very little spark line, this would indicate an open wire.
The average spark line should be measure around 1.3 – 1.8ms (milliseconds) with a relative even spark line.
If all of the cylinders spark lines measure below 1 ms and the same amount of burn time with high firing lines this means the problem has to be something that effects all the cylinders. A good example would be high resistance in the coil wire.
If there is one spark line that lower and longer than the rest, this would indicate an:
Low compression in that cylinder
Bridged plug gap
Oil fouled plug
carbon track in the distributor cap
If there is one fire line that is higher then the rest with a shorter spark duration than the rest, this would indicate an:
An open wire
Wire fell off the spark plug
Now I know everyone doesn’t have an Oscilloscope, but if you have an ohm meter as a general rule a spark plug wire should ohm at 4,000 ohms per foot.
Also never bunch wires together and run them parallel to each other, this could cause a cross fire.
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