INTERMITTENT MISFIRE IN P71

  • Tiny
  • odnrk9
  • 1971 Ford

This is for a 2001 P71. Under light part throttle accelleration, I get an intermittent misfire. Not long enough to set a trouble code, and it will go away if I give it enough throttle to downshift the transmission. I have tried a fuel system cleaner, and the plugs have been changed. I have heard of a Ford fix that was basically changing out all the coils for new ones. Could this be my problem?

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Thursday, March 22nd, 2007 AT 8:32 PM

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  • Tiny
  • odnrk9
  • Member

Anybody?

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Friday, March 23rd, 2007 AT 7:56 PM
  • Tiny
  • odnrk9
  • Member

It's a 2001 Ford Crown Victoria with 142,000 miles. It has a 4.6L engine, and it is a police cruiser. I really need the help here, as my department doesn't have a lot of funds available for repairs, so if I can fix it, I do. It also, besides the above problem, sort of surges under hard accelleration. Still has no trouble codes.

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Saturday, March 24th, 2007 AT 5:24 PM
  • Tiny
  • merlin2021
  • Expert
  • 17,589 posts

Have you done a compression test?
Does the car have coil over ignition? If so try testing the coil by changing placement on the engine. See if the misfire moves to the new cylinder. Then you'll know for shure!

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Saturday, March 24th, 2007 AT 9:47 PM
  • Tiny
  • odnrk9
  • Member

Yes, it has coil over ignition. The misfire is so intermittent that I have no idea which coil might be the culprit. It doesn't misfire while idling, just while being driven. I guess what I'm asking is could it be a fuel delivery problem, ignition problem, or both. And, how would I find out?

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Sunday, March 25th, 2007 AT 6:14 AM
  • Tiny
  • merlin2021
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  • 17,589 posts

If the engine light is on have the code read! It will tell you wich one(s) is missfiring! Autozone does it free.

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Sunday, March 25th, 2007 AT 7:38 AM
  • Tiny
  • odnrk9
  • Member

No codes. I did pull the plugs today, and the center electrode was burned off at the tip (platinum plugs). I reset the gap, as it had opened up on most of them to.060. I reset it to.054, and replaced them. It runs much better now. I guess maybe I just need to put in new ones. For platinum plugs, they surely did not last very long! Could that have been causing my problem?

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Sunday, March 25th, 2007 AT 5:37 PM
  • Tiny
  • merlin2021
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You are about to find out! How many miles are on the plugs?

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Sunday, March 25th, 2007 AT 8:37 PM
  • Tiny
  • odnrk9
  • Member

I can only guess on the miles, but I'd say about 40,000. I was under the impression that platinum plugs were supposed to last much longer. I could see where the metal from the center electrode had transferred to the ground electrode. Never saw anything like that before. What would cause that? Other than the metal transfer, the plugs looked good. No unusual coloration or anything like that.

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Sunday, March 25th, 2007 AT 9:32 PM
  • Tiny
  • merlin2021
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Melting electodes are from running to lean. HOT! Even if the car doesn't set a code you may still have dignostic info in the PCM. Especially in the case of misfires.

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Friday, March 30th, 2007 AT 4:49 PM
  • Tiny
  • odnrk9
  • Member

Thanks! I didn't replace the plugs yet, but I did reset the gap. Runs much better now, and the miss is all but gone. Still get it, but so infrequently I almost don't notice it. I'll get it to Advance Auto to get the codes read.

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Friday, March 30th, 2007 AT 9:59 PM

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