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Old 01-11-2011, 07:00 PM   #1 (permalink)
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Weird Civic misfire problem

I have a 99 Civic EX (d16y8) with 170k miles and over the last several months it has developed a bit of a misfire. It's not really noticeable on the highway, but when under light load at about 2k rpm and at idle, it is pronounced.

Anyway, I've been trying to diagnose and hunt down this thing since it started. I recently got a timing light for christmas, so I decided to check my timing and noticed something interesting, whenever the car misfires, the light fails to pulse for that cycle. I presume this means that it is just not firing.

It's completely intermittent, and does not occur at regular intervals that would lead me to believe some rotating sensor was damaged, and it jumps across all 4 cylinders.

Just for posterity and in vain hope, I did a whole tune-up (plugs, wires, cap, rotor). Nothing changed. I checked the coil, which had the blue mark indicating that the insulation had been burned through, so replaced that. No change. Read an article about how ICMs sometimes go bad in older Civics, so I replaced that with no change.

The other day I pulled the whole distributor off to inspect for damage on any of the internals, but everything looked like brand new. Not even any dust inside it. All the magnets on the sensors were clean and free of metal flakes or debris of any kind.

Unfortunately, I can find no information about this kind of problem and no test procedures for anything that's left. Has anyone else ever encountered this sort of thing with their car? Seems like usually misfires come down to air and fuel issues and not spark, so I'm totally at a loss here. The engine light never comes on, and when hooked up to a scan tool for live data, everything reads right where it should.

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