Don't always blame the coil pack!!

[MX-Drew]

Hi guys,

Well I have been suffering a misfire off and on for a few weeks and it would through CELs from random misfire to misfire on cylinder 3.

Well after trying a new coil pack, no difference, new HT leads, no difference, checked plugs etc etc etc .........

Then one day it was running really bad so prodding around the engine bay I found I could turn the misfiring cylinder on or off by moving the injector wiring loom. I removed the loom and found one of the wires was broken inside the insulation right at the connector. After repairing this then refitting the loom the car runs great.

So the moral of the story is don't always blame the coil pack. :)

[Tom @ Fast Forward]

I like it when a story has a happy ending. :)

My random missfire was similar. It was the 12V wire to one of the coils that was randomly just touching the engine. Then, a couple weeks ago, it really touched the engine and bew a fuse. Found it, fixed it and no more problems.

[maggie]

My mysterious misfire always occurs at 4100 rpm. No codes thrown.

[Tom @ Fast Forward]

Mine never threw a code either. Thta was the mysterious part. When it occured, it would just miss, pause, miss, pause,..... It would do that about 5-6 times and then not happen again for days. I would see the A/F go dead lean each pulse which led me to ignition.

[MiataMTF]

Good point, don't replace parts if you don't have to.

When my 2-3 coil started failing two years ago, first thing I did was swap the two coils. When cylinders 1-4 misfired, I knew it was the coilpack and which one was bad. Mike's place sold me a good used coil for $75 and the problem was solved.

[chuckerants]

I also had a problem with an intermittent misfire with no CEL.

It turned out to be a couple of frayed wires from the CPS laying real close to one of the belts.