WS8 Primary & Secondary Ignition Patterns

Make: Toyota. Model 4A-FE 1999

This model uses pretty much a conventional Ignition System, where there are distributor, Coil 'Bottle' and the Primary coil has its own connection exposed. All we need to do is back probing, hook it up with an oscilloscope and we are really to go with any ignition pattern.
Or, we can set up a lab scope which is pretty bulky and hairy but we will have a clearer and more functional view of all patterns.

The Objective is pretty plenty but simple: Record the Primary and Secondary Ignition Patterns in different engine's load conditions, in order to reach a verdict about the operations, or electrical characteristic of the involved components, and most important yet, what exactly happening in the circuits. This will helps us understand more deeply about the basic principal of Ignition, and thus come very handy, even critical in diagnosis.

Primary:
Idle:

RPM: 1397
Firing Voltage: 250+
Burn Voltage: ~50V
Burn time: ~1.5ms
Dwell time: 5.5ms /Angle 23deg
Status: Normal. All periods are available: Off, dwell, firing, burn, Coil oscillation, back to Off. The graph reflexes what's inside the primary coil. When Points close, the dwell time starts building up current in the coil, a constant voltage is fed (~13V=> Battery), until Points releases, that collapse the whole current and its magnetic field creating a big Voltage spike. The burn time represents how long the the spark arks across the spark plug gap. Dwell angle shows advance is 23deg before TDC.

Snap acceleration:

RPM 2442
Firing 250+ or less
Burn Voltage ~50V
Burn time: ~1ms
Dwell time 4.4ms/ Angle 32deg
Status: Abnormal. @ higher RPM, dwell time seems to stretch out but it is now longer, but shorter, so do burn time. RPM is almost as twice as when idling, but dwell time is not half of what was in idle, just less, so is burn time. Verdict: Higher RPM means less time for each cycle of ignition, given that compression TDC is every 720deg of crankshaft. When there is less dwell time, means less firing voltage, thus less burn time. The Ignition advance unit in this case the Centrifugal Advance just forwarded the dwell angle by 32deg instead of 23deg trying to compensate for dwell time loss, and it did a little good there. But still, this is not very effective as these proportional-less figures are showing.

Secondary:
Easy, there is almost no mystery at this, especially when all the tricks were discovered in the primary. But, in diagnosis, and as further more advanced Ignition System comes to play, 2nd pattern is what it takes to determine whether your system delivers a strong, well-timed spark or not, since what people care about is the result.
The secondary graph is structurally similar to primary, but every voltage here is "stepped up", by that transformer step up process.


Idle:

RPM 1337
Firing (stepped up) ~3kV
Burn Voltage ~800V
Burn time ~2ms
Dwell time 5.3ms
Status: Normally ineffective. A conventional only give out 3-4 kV and less @ higher RPM. Certainly that the vacuum advance and the centrifugal advance are not effective enough. Comparing to other electronic Ignition, its coil can step up to 20kV+, which give more complete combustion longer & hotter spark, run leaner @ idle, and waste less fuel at higher RPM.

Snap acceleration

It is different between snap acc and hold high RPM. Because Ignition pattern is more likely to be affected by engine speed than the amount of acceleration. This "high" spark can only be achieved at the first moment of RPM change. A suddenly disconnected contact breaker makes an exceptionally higher spark.

 But as acceleration stops, the higher RPM is held, then there is less dwell time, hence firing voltage should be less again:

  To illustrate the spark hence to test it in atmosphere, a spark test a carried out. Basically this is just a mechanism that simulate the spark plug, by powering one head with the 2nd output, and the other head is an adjustable screw that can increase or decrease the spark test's air gap, and hence grounded. You can see the spark with your bare eyes now.
(video)