Primary & Secondary Ignition

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. What unit of measurement are you using to measure the dwell time?

                            Milli Seconds      7ms/20%

1.6         Are all these primary ignition voltage readings normal? Yes ✓No ____  Please discuss what is normal or abnormal about this pattern and what causes it?
             
           The above pattern is the normal pattern for this primary circuit because it has dwell time, firing time, burn voltage and burn time. Abnormal pattern may miss one or more above configrations

Cyl 1	Cyl 2	Cyl 3	Cyl 4	Cyl 5	Cyl 6	Primary Ignition
300+v	300+v	300+v	300+v	-	-	Firing Voltage
47v	50v	55v	57v	-	-	Burn Voltage
1.5ms	1.5ms	1.5ms	1.5ms	-	-	Burn Time
7ms	7ms	7ms	7ms	-	-	Dwell Time

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. Record voltage and time scales.

1.8         Discuss what the primary display or parade pattern emphasizes for diagnosis. What can it help you see?
            
            The Primary display tells us how this primary circuit play a role in spark generation in spark plug through secondary wiring. It help us to see the exact voltage pattern on ignition oscilloscope and to find the fault in it if any which is effecting the engine performance

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?

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 ✓ No ____  Discuss what is happening in the pattern and what it is telling you about the ignition system.

It shows us that to create a good spark across the air gap in the plug, we need very high voltage in  very shot 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.

Cyl 1	Cyl 2	Cyl 3	Cyl 4	Cyl 5	Cyl 6	Secondary Ignition
7KV	9KV	6.5KV	7.5KV	-	-	Firing Voltage (KV)
3ms	3ms	3ms	3ms	-	-	Burn Time (ms)
4kv	5kv	4kv	4kv	-	-	Snap Acceleration

2.6 Are all these Snap Acceleration secondary ignition voltage readings normal? Yes ✓ No ____ Discuss what is happening and what the pattern is telling you.

When the snap acceleration is added, the firing voltage slightly increased. This means that higher rpm needs higher firing voltage with short burn time

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	Cyl 5	Cyl 6	Secondary Ignition (one cylinder grounded)
4.1KV	4KV	4.2KV	2KV	-	-	Firing Voltage (KV)
				-	-	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.

In this pattern, the firing voltage is very high for No. 4 plug  and burn time is very low but all other three plug having low firing voltage and high burn time.
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

2.12 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.

 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	Cyl 5	Cyl 6	Secondary Ignition (Spark tester on one cylinder)
5kv	7kv	7kv	28	-	-	Firing Voltage (KV)
1.6ms	1.5ms	1.4ms	0.3ms	-	-	Burn Time (ms)

2.14 Draw or photograph the spark tester Secondary Ignition waveform you see now on your scope. Show the detail that is necessary for accurate diagnosis. Include time and voltages.

2.15 Stop the engine, remove the spark tester (be gentle), replace the spark plug wire, and run the engine to clear the spark plug. The engine should be back to normal now.

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. 

When the spark tester is located at 20 kv (bigger spark gap) in #4 cyl , the firing voltage increases to 6 kv and the burn time decreases to 1.3ms because there was a bigger spark gap.
 As a result, the firing voltage and burn time are related to the spark gap. If spark gap is small the firing voltage will decrease and the burn time will increase. On the other hand, if spark gap is big the firing voltage will go up and the burn time will drop.

2.17 Remove the spark tester carefully, and put everything back together on the engine. Engine runs fine? ✓ yes, or ____ no. If any problems with vehicle, please tell your instructor.