Warning: Ignition coils create high voltage. It can be dangerous, so avoid getting too close to ignition parts when engine is running. Make your connections when the engine is off, and then keep your distance when the engine is running. Even some primary voltage is high enough
to stop a “Pacemaker”.
Also: Do not run engines with secondary ignition HT leads “open circuit”. Make sure they are grounded to engine through a spark plug, grounding wire, or spark tester.
If you have problems with the task, see you lecturer for help.
1.0 Primary Voltage Patterns
1.1 Set up a lab scope or ignition oscilloscope to view the primary ignition pattern (in parade or display mode) on your lab scope, with the engine warmed up and idling.
1.2 Record the average Firing Voltage (or “Step Up voltage) for each cylinder in the chart below. Some variation is normal, just pick the average. If you don’t understand what this is, review the resource information available.
1.3 Record the average Burn Voltage for each cylinder in the chart below.
1.4 Record the average Burn Time in milliseconds for each cylinder in the chart below.
1.5 Record the average Dwell Time for each of the cylinders in the chart below.
1.6 Are all these primary ignition voltage readings normal? Yes.
Please discuss what is normal and what causes it?
Obviously each cylinder have the same pattern, if we notice carefully only cylinder 1 have little bit different other about after burning time, so far I can say it is normal and have back EMF. May be causing the spark plug worn.
| Cyl 1 | Cyl 2 | Cyl 3 | Cyl 4 | Primary Ignition |
| 250+ | 250+ | 250+ | 250+ | Firing Voltage (V) |
| 40.7 | 40.7 | 40.7 | 40.7 | Burn Voltage (V) |
| 1.01 | 1.01 | 1.01 | 1.01 | Burn Time(ms) |
| 5.35 | 5.25 | 5.41 | 5.45 | Dwell Time(ms) |
1.7 Draw or photograph the Primary Ignition oscilloscope parade pattern from your scope into the box below. Do it carefully and show the detail you need to see for diagnosis.
1.8 Discuss what the primary display or parade pattern emphasizes for diagnosis. What can it help you see?
From the oscilloscope above:
Point A is Dwell time: primary coil is grounded and the current coming through to the coil to charge the magnetic field.
Point B is Firing voltage: the magnetic field collapse in the primary coil and create high voltage to cross jump between electrode to the ground.
Point C is burn time: time is needed for energy dissipated.
Point D is Oscillation.1.10 Some scopes have the facility to use raster or stacked display. How could this help you to diagnose a fault. What can you see more clearly?
Possible of misfiring, bad earth, checking the burning time and we can compare the electrode firing on the spark plug for each cylinder. All these effect to engine performance.
2.0 Secondary Voltage Patterns.
2.1 Set up your ignition oscilloscope or lab scope to view the secondary ignition patterns on your lab scope, with the engine warmed up and idling. (Use parade mode or individual mode on each different cylinder, depending on scope available.)
2.2 Record the average Firing Voltage (or “Step Up voltage) for each cylinder in the chart below. Some variation is normal, just pick the average. If you don’t understand what this is, review the resource information at the back of this worksheet.
2.3 Record the average Burn Time for each cylinder in the chart below. Are all these secondary ignition voltage readings normal? Yes.
Cylinder 1:
Cylinder 2:
Cylinder 3:
Cylinder 4:
2.3 Record the average Burn Time for each cylinder in the chart below. Are all these secondary ignition voltage readings normal? Yes.
Discuss what is happening in the pattern and what it is telling you about the ignition system.
To create the spark jump across from electrode to ground need high voltage and short time.
2.5 Do a Snap Acceleration (don’t damage the engine by revving too high or for too long) and record in the chart below how high the Firing Voltage (KV) went under Snap Acceleration.
The pattern below showing one of 4 cylinder:
| Cyl 1 | Cyl 2 | Cyl 3 | Cyl 4 | Secondary Ignition |
| 12.1 | 12.3 | 14.1 | 15.2 | Firing Voltage (KV) |
| 0.22 | 0.14 | 0.12 | 0.15 | Burn Time (ms) |
| 12 | 15 | 14 | 15 | Snap Acceleration(KV) |
2.6 Are all these Snap Acceleration secondary ignition voltage readings normal? Yes.
Discuss what is happening and what the pattern is telling you.
When we snap acceleration, fuel and air more coming than idle, at the time electron need energy to jump across, automatically firing voltage going higher and burning time less and less. Why less? because the energy burned will quickly disappear.
2.7 Draw or photograph the Secondary Ignition lab scope pattern while idling from your scope into the box below. Do it carefully and show the detail you need to see for diagnosis.
2.8 If you can safely do this, (with the engine stopped), gently disconnect one spark plug wire, and short to the engine with a jumper wire. Which cylinder number did you short? 4
2.9 Start the engine and let it idle (for only a short time.) Record the new Firing Voltage and Burn Time for all the cylinders in the chart below.
| Cyl 1 | Cyl 2 | Cyl 3 | Cyl 4 | Secondary Ignition (one cylinder grounded) |
| 6.8 | 7.1 | 7.1 | 16.9 | Firing Voltage (KV) |
| 1.45 | 1.32 | 1.37 | 0.7 | Burn Time (ms) |
2.10 Draw or photograph the shorted Secondary Ignition waveform you see now on your scope.
2.11 Discuss what is happening in the shorted ignition pattern and how the ignition pattern tells you what it is happening in the ignition system.
On cylinder no 4 firing voltage higher and the burning time shortest than other 3 because the ground wire has been shorted to the engine and in the same time need high voltage to push or force the spark across, automatically burn time will be short.
2.12 Remove the ground wire and attach the spark plug wire back on the engine so it is normal again. Run the engine a bit to clear the spark plug.
2.13 Stop the engine and attach a spark tester to another spark plug wire. Start the engine and let it idle (for only a short time).
Record the new Firing Voltage and Burn Time for all the cylinders in the chart below.
| Cyl 1 | Cyl 2 | Cyl 3 | Cyl 4 | Secondary Ignition (Spark tester on one cylinder) |
| 5.9 | 13.3 | 5.6 | 5.31 | Firing Voltage (KV) |
| 1.46 | 1.46 | 1.83 | 1.83 | Burn Time (ms) |
2.14 Draw or photograph the spark tester Secondary Ignition waveform you see now on your scope.
2.16 Discuss what happens to the ignition waveform when the spark tester is attached to the spark plug wire. What does it tell you about the ignition system.
We remove the spark plug wire from cylinder 2 and attached spark tester, The spark park tester gap can be adjusted, the picture above (wider gap) test for the second time after we test the small gap. The spark still jump across but need higher voltage and the burn time will be short. The table above showing the firing voltage higher than other.
2.17 Remove the spark tester carefully, and put everything back together on the engine. Engine runs fine? Yes.
Note: remember, all the experiment above about string theory where is the firing voltage high and the burn time will be short. Vice-versa.
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