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car still misfiring


98deville

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The wires are often the problem ...

but are you saying that replacing the plugs seemed to fix the problem temporarily ??

uhh, others will chime in, but I would recommend that you replace the wires.

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I would have inspected the plugs and replaced the wires for a miss. That includes doing a resistence test on each wire to ensure that I found the culprit. Sometimes resistence testing will not expose that a wire is a problem, heat along with their proximity to grounds cause their insulation to break down. Wires that feel dried out, brittle and that have burn marks on them from arching and leaking high voltage to a ground should be replaced.

Probably what happened is that you disturbed the wires when you did the plugs, and eventually they began finding a ground again or there is a bad connection at the coil end or plug end.

Currently I don't have a miss, but my wires are exhibiting insulation breakdown and I am sure I will replace them soon. I plan to go to my local scrap yard and remove the high temp wire loom off of late model cars along with retainers, etc. The crap you buy at auto parts stores melts.

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I had something similar happen afew years ago. Replacing the plugs helped but the misfire returned. Replaced the wires helped but the misfire returned. It turned out that one of the boots had a scar and allowed carbon tracks to form on the ceramic of the plug. New plugs solved the problem until the carbon track formed and allowd a ground. New wires helped, but the carbon track was already there and it didn't take long for the misfire to continue. If you decide to replace the wires, make sure you remove the plugs and check them carefully.

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And if the old plugs where carbon tracked, the boots were as well. So the new plugs will then get carbon tracked from the old boots.

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  • 2 weeks later...

A carbon track is a carbon trail left on the side of the plug from the spark finding its way down the side to ground itself on the plug base. It will look like a hairline crack in the porcelain.

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