2000 Grand Cherokee Cyl 5 Misfire

YJJPWrangler

Well-Known Member
Joined
Jul 19, 2005
Location
Charlotte
Wifes 2000 Grand Cherokee(4.7L) keeps throwing a cylinder 5 misfire. I pulled the spark plug and some of the porcelain was missing. Replaced plug, reset computer and after about 20 mins of driving it the CEL came back on again. I had the same issue with it last year and replaced the plug and the coil pack. Coil pack looked brand new when I put it back together. Anything else I'm missing? Could it just be a bad coil pack(again)? I also had to replace the upstream O2 sensor this weekend as well but that should affect anything.
 
Try swapping the #5 coil pack with another and see if the miss fire follows the original coil pack. If it does..then bad coil pack. Also another way to speed up the misfire, is to load up the engine. Example, try to power brake with out breaking tires loose. Keep engine loaded and misfire should set off engine light.

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I have done that before when it first started acting up. It was still giving me a cyl 5 misfire. Can't do much with it during the week but will try and look at it again this weekend.
 
I usually inspect the coil boot internally. If any doubts I put a new coil in, and test. If misfire persists, it's not the coil. Easier than swapping coils and more error proof due to not introducing unknowns imho. Along with a new plug. If the old plug was black, did you replace it and it run fine for a bit? I've seen fish injectors bleed and cause misfires on startup. (And foul the plug). Also worth performing a compression/leak down test if the above was already done.
 
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