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Help! P0304 cylinder 4 misfire

40K views 18 replies 12 participants last post by  SteelBlueWK 
#1 ·
Driving on highway and suddenly feel like i am on rumble strips and instantly get the p0304 cylinder 4 misfire. What do i have to change out? Jeep wont go over 55 without shaking
 
#6 ·
My friends 4.0 2001 Cherokee had a recurring cyl 3 mis fire until he replaced the injectors then it came back again and they changed the coil packs and its been gone for a few years so it could be either.
 
#8 ·
better yet swap your plug to cylinder 1, swap your coil to cylinder 2 and swap your injector to cylinder 3... then drive it and see if the code follows either one of these items ;)
 
#12 ·
I had misfire on my Sierra, turned out it was cracked spark plug, had all new plugs installed and the mechanic kept putting the old plug back in... errr took it to different dealership and he told me it was cracked plug, replaced it, all better now.
 
#13 ·
I have a 2002 Jeep with a similar problem. It had a small ticking sound on the driver's side of the engine and would cut out when I went to pass someone or accellerate at a fast rate. If I backed off and gradually accellerated, it would do just fine. I used fuel additives in it and it seemed to be running smoother, but the fast accelleration in gear still produced this problem. Last night I went for a ride and about 20 minutes into the ride, I came up on a stop sign and from that point on, it acted like one of the cylinders was misfiring constantly. I got home and shut it off and refired it with the hood up and it was still there. This morning, i went out and restarted the engine and the misfire seems to have gone away. I had it checke dthe other day and the codes showed an intermittent misfire on the #3 and 4 cylinders. I drove it on a 120 round trip and got a little over 14 mpg, which was up from about 11 mpg before I had added the fuel treatment. I feel it is probably either an injector problem or maybe old fuel (The car sat for about 6 months and had 1/4 tank of gas in it) I filled the tank right after getting it and added fuel treatment. I was gonna try adding a injector cleaner to the gas to see if that was the problem. Any other suggestions?
 
#14 ·
I forgot to add that when I reved the engine while it was out of gear before adding the fuel additives, it would sputter at higher RPMs but after adding the treatments. I tried it yesterday before going on the ride and the sputter seemed to go away. On the ride last night, the hesitation came back. I couldn't find a vacuum leak, and wonder if a vacuum leak might be the culprit.
 
#19 ·
I used Chevron Techron cleaner in combination with Sea Foam cleaner. Can be found at most auto parts stores. If this doesn't clear the injectors, then a professional cleaning by dealer or local repair shop would be needed.
 
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