Jeep misfire


Asked by Guru9TW6C Jun 25, 2018 at 08:30 AM about the 2002 Jeep Grand Cherokee Limited 4WD

Question type: Maintenance & Repair

So my jeep wj 4.7 has a tiny misfire at idle
only when warmed up . It doesnt do it
when cold and idle slighty flucuates also.
Sparks plugs are good, air filter tps, no
vaccum leaks iac and throttle body are
clean not sure when coils were changed
though, also i dont think the misfire is
related to idle flucuation because it
flucuates when cold but idles fine .

12 Answers


When we’re the fuel injectors cleaned professionally?

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No clue. I figured it might be a coil going bad and not working right when hot

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When it reaches operational temperature the fuel/air ratio leans out, if an injector is slightly plugged it may deliver a good pattern when at a longer pulse width cold but gets abnormal when it leans out warm.

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Should i try running some seafoam ? .... should i go ahead and replace all 8 coils is it possible thats the problem ?


I used Seafoam on my old Tahoe that would get a random multiple misfire code, it was not the spark plugs as they were new, used two cans in two tanks of fuel, then went to a bottle of Techron every other fill up and had no more problems with random multiple misfire or a check engine light, but as the fuel had changed to E10 I just kept on using Techron additive right up to the day I sold it.

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So i already put seafoam in my gas tank last time i got gas im almost down to half a tank now . Should i get annother can next fill up ? Do u think it would accuatly clean injectors if thats whats causing the misfire ( its very small) also no codes either


It cleaned mine, and yes I would try one more bottle on your next fill up. If it still has a misfire it could be a faulty plug, or a leaking boot. Wait until some dark night and start it and look around for spark leakage, sometimes spraying water around the ignition areas will show something.

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I just drove it down the road and when i parked it , it was at operating temp and idle was only flucuating a tiny bit and idle was sounding good i didnt hear the tiny misfire that sounded like a cough. so i think the seafoam is working nicely as the closer i get to empty tank ( i have bout half now )


You may have to clean the throttle body with throttle body cleaner to stabilize the idle if it becomes a problem. Sounds like your on the right path.


Did that not to long ago cleaned throttle body and Iac , just changed tps . And recently checked plugs and gaps they almost look new thats why iv pretty much narrowed it down to coils and injectors

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