Weird misfire
12-12-2015, 06:49 AM
#1
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Year: 2004
Model: Grand Cherokee
Engine: 4.0
Weird misfire
Hi guys was wondering if you could help me out.
My 04 WJ 4.0 has this weird misfire it started about a week ago when I start it the engine will misfire and shake but if I hit the gas pedal and be fine the rest of the time I drive it? It's done it to me about 4 times since last week.
Any thoughts?
My 04 WJ 4.0 has this weird misfire it started about a week ago when I start it the engine will misfire and shake but if I hit the gas pedal and be fine the rest of the time I drive it? It's done it to me about 4 times since last week.
Any thoughts?
12-12-2015, 11:07 AM
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Year: 1996
Model: Grand Cherokee
Engine: 5.2L V8
Any of your plugs really fouled? When I first got my truck it would shake violently when started and when at about 45 miles an hour. One of my plugs was extremely fouled and nasty so I replaced it with a new plug and that fixed it. Amazing what that one chuggy cylinder would do. Maybe it could just be a cheap plug? One could hope.
12-12-2015, 12:39 PM
#3
Old fart with a wrench
That's really odd! I just put a new set of Champions in my 4.0 about 5000 miles ago and I'd gotten an occasional misfire under heavy load, like bad plugs. It got steadily worse until it set a code P0303, misfire cylinder #3. I pulled all of them out and changed them with NGKs. 5 looked good, but #3 had a heavy coating of light brown carbon on it, so I chipped it away to find the center insulator had a crack in it. It must have had a fine hairline crack in it when I put it in and I didn't notice it. This may have been caused by rough handling before I got it, but my confidence in Champion was shattered. I'll let you know how the NGKs work out. So far I have about 1000 on them. Running smooth as silk.
12-12-2015, 01:01 PM
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Ok so driving around been fine I went to advanced auto use the scanner and I have a pending code for misfire cylinder 3. Hoping it's the spark plugs be use I've had my WJ for about 7 months and never changed them and who knows the last time the PO changed them
12-13-2015, 04:10 PM
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Year: 2004
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That's really odd! I just put a new set of Champions in my 4.0 about 5000 miles ago and I'd gotten an occasional misfire under heavy load, like bad plugs. It got steadily worse until it set a code P0303, misfire cylinder #3. I pulled all of them out and changed them with NGKs. 5 looked good, but #3 had a heavy coating of light brown carbon on it, so I chipped it away to find the center insulator had a crack in it. It must have had a fine hairline crack in it when I put it in and I didn't notice it. This may have been caused by rough handling before I got it, but my confidence in Champion was shattered. I'll let you know how the NGKs work out. So far I have about 1000 on them. Running smooth as silk.
12-13-2015, 04:51 PM
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I'm also going through a misfire issue right now. I have no symptoms except for a check engine light! your symptoms sound like a crankshaft position sensor or carbon build up on the exhaust valves. have you done a compression check of that cylinder? should do that before you put a new plug in there!
12-13-2015, 05:30 PM
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I'm also going through a misfire issue right now. I have no symptoms except for a check engine light! your symptoms sound like a crankshaft position sensor or carbon build up on the exhaust valves. have you done a compression check of that cylinder? should do that before you put a new plug in there!
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12-23-2015, 04:09 PM
#8
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Ok so I replaced the the spark plugs with Champion coppers from the dealer and I also replaced the cam sensor also from the dealer. The spark plugs looked worn so I'm hoping those were the problem it's been 3 days and hasn't done it yet so fingers crossed!
12-23-2015, 08:37 PM
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I am also having a problem with a misfire ...just purchased a 2004 WJ 4.7 from a mechanic who said it was from a customer who had serviced there...after I purchased it ( last week ) my engine light came on for a code 0302...misfire in cylinder 2...i brought it back to him today...he thought it might be a bad aftermarket coil that he had just recently replaced but decided that it might be carbon buildup on the valve...he fogged the intake system and I've driven it for about 70 miles so far....hopefully tomorrow the light won't come back on...I would appreciate any other help if someone has other ideas
12-23-2015, 09:14 PM
#10
Old fart with a wrench
There is a Factory Service Bulletin about misfires cause by carbon buildup on the valves. Check it out.
12-26-2015, 02:58 PM
#12
Old fart with a wrench
JMHO, but that looks pretty much normal. Just make sure you don't overtorque those plugs and change them at regular intervals. One of the other guys that deliver newspapers with me just had a plug blow out of the head, taking all the threads and the coil with it! It left a sizable dent in the hood.
01-04-2016, 09:03 PM
#14
Old fart with a wrench
OH...WAIT!! That guy I told you who had the plug blow out was a 4.7!