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Weird misfire

Old 12-12-2015, 06:49 AM
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Default 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?
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Old 12-12-2015, 11:07 AM
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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.
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Old 12-12-2015, 12:39 PM
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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.
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Old 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
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Old 12-13-2015, 04:10 PM
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Originally Posted by dave1123 View Post
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.
just got some champion coppers gonna put them in tomorrow and I will let you guys know
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Old 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!
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Old 12-13-2015, 05:30 PM
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Originally Posted by mobile-command-unit View Post
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!
no haven't done a compression test I'm gonna do that tomorrow as well
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Old 12-23-2015, 04:09 PM
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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!
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Old 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
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Old 12-23-2015, 09:14 PM
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There is a Factory Service Bulletin about misfires cause by carbon buildup on the valves. Check it out.
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Old 12-26-2015, 11:25 AM
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I thought I posted a pic of the #3 plug but I didn't so here it is I wanted you guys to opinion on it

Weird misfire-image-1422396482.jpg
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Old 12-26-2015, 02:58 PM
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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.
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Old 01-04-2016, 07:44 PM
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How did the other 5 spark plugs look in comparison?
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Old 01-04-2016, 09:03 PM
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OH...WAIT!! That guy I told you who had the plug blow out was a 4.7!
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Old 01-05-2016, 04:56 AM
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Originally Posted by Clayto1332 View Post
How did the other 5 spark plugs look in comparison?
looked pretty much the same
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