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Old 05-10-2016, 08:15 PM   #1
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Default Diagnosing a bad coil circuit?

So... A bit of a long story. I bought my 99 with ms2 installed (supposedly built by brain) been running a few years without issue. Moving towards turbo I installed rx8 injectors, which went well, everything was running, did a brief tuning drive, all good. The next day I start it up and idle a minute before it goes crazy rough, lost one side of the stock coil pack. Take off coil pack and note a melted up connector on the 1-4 coil. Being a little stupid on occasion, I ignore the melted connector and plug in a spare coil pack. On crank I hear a pop, no start, pretty sure I toasted coil pack 2.

At this point I figure there must be a short in the wiring that I jostled into existence or at least prominence when moving the wiring around to install injectors. Wiring is bad, coil toast, sounds like a good excuse for ls2 truck coils. Fast forward to the present... D585 coils, hack job mounting, new plugs and wires, I've spliced into the stock harness just after the plug at the front of the engine (wired for batch, theoretically bypassing any wiring that would have been impacted by installing injectors) adjust settings aaaand no start. I pull the plugs to check for spark, 2-3 are sparking 1-4 are not. I swapped connectors and confirmed that all 4 coils and plugs are functioning.

So it would seem I'm not getting a good trigger signal for 1-4. Is there a way to check this without a scope? I tried the multimeter but it's hard to make sense of anything. Secondly, if I do find there is no trigger signal, is this something that can be repaired?

Last edited by slowcarfast; 05-10-2016 at 08:52 PM.
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Old 05-11-2016, 07:50 AM   #2
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So I had a thought. If I unplug the coils and use output test mode with a super long dwell (a second or two) perhaps I could get a useful reading on the trigger wire using a multimeter.

Is there any risk of damage to the megasquirt by doing this? I can't think of why there would be, but I am far from an expert on electrical matters.
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Old 05-25-2016, 08:24 AM   #3
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So I finally pulled the megasquirt to poke around. Nothing is visibly burned out, which was a bit of a long shot anyway. Is there any way to test the daughter board? At this point in contemplating just buying the diypnp for sale in the classifieds to get the car running while I try to figure this out, then selling one of them once o get it sorted. My primary concern with that is if the previous owner did some wiring gymnastics on the vehicle side to get things working. Then it might not be so pnp. Braineack do you keep wiring diagrams our something from old builds that you would be willing to share to help me figure things out? This was built for user 94mx5red.

Last edited by slowcarfast; 05-25-2016 at 09:31 AM.
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Old 05-28-2016, 09:00 PM   #4
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Well, I figured it out! Megasquirt is fine, my issue was a combination of bad wiring and incorrect use of the output testing function. When I first got a no start condition after installing LS coil I expect there was a short in the trigger wiring. As I tried tapping into the signal wire at various points in the harness I believe I was using the output test til wrong. I thought I read that selecting coil b,c,d or whatever in the output testing dialog would also trigger the preceding coils. So selecting b would trigger a and b. This was not the case, at least four my configuration. So most of my testing wasn't actually outputting a signal to A when I thought it was. Ended up running new wire ask the way to the boomslang, which may not have been necessary, but hey, it runs! And I'm excited enough about that fact that I may have the motivation and time to finally install my turbo this weekend!
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