lhutter1

Hey guys!

I'm new to the group with a (new to me) 2004 Grand Cherokee Limited. I've noticed that I seem to have an intermittent misfire of sorts. Only happens under humid or damp conditions, sounds like one cylinder. Can hear/feel on acceleration. On a clear day, she runs great! I've seen many posts about head gaskets and fuel injectors and such, but those all seem like more permanent issues. This seems to be pretty predictable with the forecast. Any known cracked coil issues or wiring issues I should look into? Thoughts? Oh, and there's "no" check engine light at the time of failure...

Thanks!
Lorne

Bustedback

Check the spark plug boots for signs of burned spots where the spark has leaked out.

Hymie

If it is due to an electrical breakdown of one or more of the coils – then spraying with a proprietary moisture inhibitor (such as WD40) should cure the fault (temporarily).

However it could be some artefact of the air humidity (water content) within the cylinder causing a misfire (possibly due to a partially fouled spark plug and/or incorrect spark gap).

lhutter1

Well, I finally had a chance to play with Jeep. I changed the plugs and it's better for sure. What a PITA that last one on the passenger side is! lol I was amazed the thing even ran after looking at the old plugs! There had to be close to .100" gap! All the way down to the insulators. Unbelievable! lol All looked good color, no oddities. Anyway, mucho bettero (that's French I think)! Coils all looked to be in excellent shape. There's still something about when it heats up, but it may just be exhaust vibrating or my imagination.

Thanks all!
Lorne

rizmonkey

I just had mine replaced and mine were gapped at .080"..... Who does that ?!?!?!? Don't people know anything about cars anymore??

RIZ

lhutter1

Wow, someone gapped yours that way??? Yikes! Mine were just that worn. I've seen many a bad plug, but I ain't never seed nuttin like that! lol

lhutter1

Update: Well, I thought I had it with new plugs(no doubt it runs better than it did)...

OK, it appears that when the ambient temp is below say 65ish degrees "F" it seems to have the illusive misfire once the engine warms up. Starts and runs good cold, then becomes louder and misfires as it warms up. No codes. If the ambient above 65ish degrees it runs great (smooth and quiet) warm or cold engine. The cold temps just happened to coincide with the damp weather. Ideas?

Thanks!
Lorne

lhutter1

Well, I took it to a friend's shop and we put a scope on it. No misfires recorded, but it was obviously missing and the engine stumbling and jumping around. The only thing noted out of spec was the IAT sensor was reading 108 degrees "F". It was either the driest 108 degrees I've ever felt, or the sensor's faulty and it was really only 60 degrees. I'm going with the second of the two. lol We unplugged it and it dropped down to 84 degrees (guessing it's a default). Seems to be a little better, but still not right. Maybe a new sensor will fix it? Am hoping! Anyone else seen this?

Lorne

lhutter1

Hmmm... No responses or comments? Can anyone see this?

Thanks,
L.

dave1123

Oh, I can see it. I just don't want to make a guess unless it's constructive.

lhutter1

Good call, thanks!