Megasquirt Voltage Spike, any thoughts? Options

[yarin]

I datalogged a few runs and found the issue to my random ignition hitch. Previously I thought the tach signal was dropping out, but you certainly cant argue with this data...

My MSII is grounded to one of the tranny bolts. The tranny groud strap was just changed and cleaned up. +12V is connected to the battery cutoff switch (I think where one of the terminals where the alternator plugs in, i'll double check). Is this OK?

A voltage spike (both up and down) causes Pulse Width to max out, maxing out injector duty cycle, resulting in a quick cough. This occurs once in a while, sometimes every 30 seconds, sometimes not for a few minutes. Voltage never spikes at idle, only when driving at mid rpm.

Could it be a bad connection? (then i would assume the spike would be unidirectional).
Bad voltage regulator on alternator? The battery charges fine, normal operating voltage is ok.

These are about 1/10th sec samples from datalogging:

13.4 13.5 13.3 13.3 21.5 13.9 13.5 13.5 13.3

13.9 13.6 18.6 14.8 13.9 13.9 13.7 14 14 13.7 13.5 8 13.2 13.5

Any thoughts? Where my MS experts at?

Thanks

[Twystd1]

We had a discussion at the club site on a ECU issue on Randals car.

I have see this same stuff happen on several aftermarket EFI systems.
It is all about grounding issues and spurious signals going into the ecu by means of high voltage circuit. (read: plug wires and coil)

Simply using the wrong spark plugs (resistor VS non-resisitor) can make this stuff happen. So can resistor wires VS solid core wires.

I just plagiarized this from DNHunt without his permission. I hope he doesn't mind.

I'm not sure if this will help but, I had a bunch of problems with my car with EM noise from the ignition. Changing to resistor plugs cleaned it up. Routing sensors wiring away from sparkplug wires can help and sheilding cables can help especially if the tach signal to the ECU is weak. I use a VR sensor and signal strength is very weak and it must be sheilded. Another thing, if you are using sheilded cable only ground the end at the ECU and ground it to the same ground as the ECU. This helps prevent ground loops. Keep the ground points to a minimum. Some sensors ground to the engine case and you can't do anything about those but, try to bring all grounds back to the ECU if possible. It may seem simple to ground things like the TPS and MAP sensor to the nearest point but, don't do it, these are referenced voltages. Try not to have extra unused wires in your harness as these may increase noise.

Kind of a ramble but, I had to learn all of these things the hard way."

So there is some more food for thought...

Clayton