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Old 09-29-2010, 12:26   #1 (permalink)
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cylinder miss fire and oil on plugs

I have a '97 Crown Vic that was misfiring on cyl 7 (and giving catalytic error codes). I changed out all the plugs. There was oil in 5 of the 8 plugs. After changing the plugs the car runs even worse than before. Very little acceleration, backfires, and the driver side cat converter glows red hot after a trip around the block. I figure that the oil that got into the cylinders would make it run rough for a while, but I think that I've run it long enough for the oil to burn off. Do I need to let it idle for a while or is something else wrong. Changing the plugs was the only thing I did to it. I let it sit for about 2 hours, and it ran really smooth for a while then started losing acceleration and I could smell the cat converter heating up.
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Old 09-29-2010, 19:45   #2 (permalink)
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Re: cylinder miss fire and oil on plugs

Was the oil on the firing tip? If you're close to an Autozone, get there quick and have them check for codes.
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Old 09-30-2010, 05:09   #3 (permalink)
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Re: cylinder miss fire and oil on plugs

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Was the oil on the firing tip? If you're close to an Autozone, get there quick and have them check for codes.
No, the tips looked fine. There was no oil on the tips and all the plugs looked to have normal wear (almost none as I changed them ~6 months ago). The codes were P0420, P0430 (cat deficiency) and P0307 (cyl 7 misfire). Since the car runs really smooth when cold I know that all cylinders are firing. I believe that what's happening is that when as it runs the cat conv. is plugging up and creating back pressure that is killing my acceleration and heating the conv.
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Old 09-30-2010, 07:53   #4 (permalink)
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Re: cylinder miss fire and oil on plugs

It sounds like you need to replace the cats. If you check the vacuum at idle then raise the RPM to about 2500, the vacuum should drop to around 10" and raise back to almost where it was at idle. If it stays low, you have a plugged exhaust.
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Old 09-30-2010, 15:48   #5 (permalink)
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Re: cylinder miss fire and oil on plugs

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It sounds like you need to replace the cats. If you check the vacuum at idle then raise the RPM to about 2500, the vacuum should drop to around 10" and raise back to almost where it was at idle. If it stays low, you have a plugged exhaust.
Removed the left hand side Cat today and several pieces of honeycomb fell out. I will take this as a good sign that it's bad. Thanks for your help. I'll post back when/if this solves the issues.
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