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post #1 of 4 Old April 11th, 2017, 09:28 AM Thread Starter
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91 LX Misfire

Symptoms: Surging idle, runs like it has a dead miss through all RPM. Put a timing light on it, looked like I had spark going to all cylinders. Checked the plugs, none looked too bad, gap was in spec. Replaced plugs, now ran like it had two dead cylinders. No active faults; a few stored ones I don't recall off the top of my head, nothing that would normally associate with misfire.

Next steps:
Compression test.
Try to determine which cylinders are dead by disconnecting injectors.\

Any tips, particularly on ignition? I can do distributor, I can do COP, but this 8 plug DIS nonsense is some serious clusterfuckery. I know it's waste spark, but it also has two banks. Do they fire simultaneously or are they staggered? Is one primary or are they completely redundant?
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post #2 of 4 Old April 11th, 2017, 06:10 PM Thread Starter
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Update: Went to go take it into the garage today- and it ran perfectly. Took it out for a hot lap and got it nice and warm. Still fine. What the fuck.

Only thing I can think is today's ambient temperature is 15-20 deg F cooler than yesterday. Possibly a thermal failure of an electronic component, like oh, say an ignition module? I can't diagnose it definitively though, unless it acts up again.

I am tempted to replace the coil packs though. The front looks like it's original and the other appears to be non-OEM with a crack in it.

Any experience with this nonsense?
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post #3 of 4 Old April 14th, 2017, 07:53 PM Thread Starter
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Another hot day, and it started running on 2 again in the hot weather. Fine in the morning, started acting up in the afternoon heat. I put the timing light on it and was able to determine several different cylinders from both coil packs had erratic spark. I highly suspect the ICM. I wanted to probe the wires that signal the coil pack but the engine is jumping around waaaaaay too much to pull that off. Going to try throwing an ICM and coils at it and we will see.
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post #4 of 4 Old April 26th, 2017, 11:16 AM Thread Starter
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Update for the dozen or so people out there still driving 2.3s:

ICM was replaced. No problems since.

Coils replaced. Idles/revs noticeably smoother.
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