non-suppressed or noisy ignition systems on the dyno

Includes MoTeC CDIs, Ignition Expanders

non-suppressed or noisy ignition systems on the dyno

Postby vprtech on Sun Dec 24, 2017 9:46 am

Although not specifically MoTeC related, I thought I would post this topic here since it has to do with issues relating to high output ignition systems. Currently I’m in a situation where I need to run older 1970’s era Porsche engines (e.g. 935 Turbo) that have little or no secondary ignition noise suppression, on our engine dyno. The most recent engine, I ran with CDI (Bosch 8 pin with reluctor trigger), non-resistor spark plugs, solid core wires, and no resistors at the spark plug connectors. This is the way the engine ran in the car when new. Bosch somehow engineered the CDI boxes to work even with all of that noise. Although configuring the ignition system to a different specification (such as suppressed ignition wires, spark plugs, etc.) seems like the obvious solution to resolve this issue, it also somewhat defeats the purpose of testing the engine on the dyno, since it is desired to run these engines in their original configuration in the car. Additionally this would add unwanted labor and material costs to the dyno process.

When I ran this engine, I observed the following problems:

1. Dyno RPM encoder intermittently dropping out.
2. Random CAN communication faults between the dyno I/O and the dyno controller.
3. The lambda meters intermittently working, and continually throwing error codes.
4. The 5 gas analyzer intermittently working and then not working, finally dying altogether.
5. PICO oscilloscope would only stay connected to pc for several seconds when within a few feet of the ignition modules or coils ( I was measuring signal from distributor pick-ups at idle speed).
6. Video camcorder screen distorting when within a few feet of the running engine.

Over the course of three days, we were able to successfully finish running the engine. The last day we ran, it seemed as though we had less issues with noise. I also observed that the noise somehow built up over time, that is, when the engine was first started, the noise issues seemed less oblivious as compared to having run the engine for a half hour or so. I have since read that certain forms of electrical noise are negated by higher humidity levels, especially at or above 60%, possibly this was influencing the amount of noise I was seeing. The only other measure I took while running was to bring in an additional battery, separate to the one normally used on the dyno, and connect the engine, and engine ignition system directly to that battery, as well as adding additional ground cables from the engine to the battery. It’s hard to say if this helped or not.

I don’t have much experience with high output CDI ignition systems or magnetos, but figure that people here tuning or running engines on the dyno that do, even with some degree of ignition suppression, may have run into similar problems. I am interested and would appreciate in anyone sharing their experiences, ideas or methods that they have found to work in getting around these types of noise issues either on a chassis / engine dyno, or for the purpose of getting reliable data from sensors used for instrumentation in the vehicle.

Thank you.
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