Contour Enthusiasts Group Archives Forums Modifications Forced Induction Misfire Problem....

Originally posted by Swazo:

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I've been getting a misfire here and there. It will happen in either the #1, 3 or 4.

I've done a compression test, and all is still good.

I've got some older Bosch plug wires that replaced the FMS plug wires that crapped out. I am getting the Mangacor 8.5mm wires today.

I'm going to get an additional ground strap for my coil pack to make sure it's grounding well. I'm planning on pulling and double checking the plugs gap (.35") to be on the safe side. I've got the NGK iridiums in a stock heat range. If it still misfires once all of these steps have been taken, I was thiking of trying 1 step colder copper (cheap way to find out...) plugs to see if that cures the problem.

Any other ideas?

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Good god! Why such a tight gap, that can also lead to a misfire. IF you aren't getting a misfire under heavy load and high boost, then gapping the plugs closer is a bad idea. Do a search for an old post I made about plug gap where I expained it to the best of my own understanding.

I run 0.045" to maybe 0.047" and I was able to boost 14psi on a 10:1 compression motor! So how come there were no misfires there...on Autozone Duramag wires to boot?
Well, because the spark generated by our ignition coils is more than strong enough to jump the gap.

The misfire is probably due to plug wires, Gap between 35-55 thousandths seems to have very little effect on misfiring other than the smaller the gap the lower the energy of the spark.
So that means you want the most spark energy which would be the largest gap without a misfire under boost.


EDIT**************

I also forgot to point out that I took out my NGK TR6 plugs and am running autolite double plats. Almost a completely stock setup except a slightly smaller gap.

Sometimes tuning can be at fault too, if it is running a bit too lean or too rich it can misfire. Lean misfire would be more common, especially if secondaries are removed and not been compensated for.