Misfire please help?
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New User
Joined: Aug 2000
Posts: 7
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From: Missouri
Misfire please help?
I have a 96 Ford F150 with a 4.9L 300. At idle it has a definite misfire (you can feal the truck shake). It runs fairly well at highway speeds, however. When I pull the codes I get a code 302. I have changed the plugs and wires twice (with Motorcraft wires and plugs) but it still shows a misfire on cylinder 2. The compression is 150 on this cylinder and I have replaced the fuel injector. I took it to a mechanic and the only thing that he could think of was that it could be a valve guide starting to wear or beginning of a burnt valve. He checked the timing and said it was fine and said that one of the other cylinders is missing fire every second beat once it warmed up. It doesn't currently show a code for this only a 302. Previously I had a code 420 but after resetting it hasn't returned. I have searched the forums and have discovered that this has frustrated quite a few people. Any suggestions would be greatly appreciated.
Post Fiend
Joined: Jan 2004
Posts: 5,377
Likes: 2
From: Elkhart IN
well, when you get a leak down tester, and you fill the cylinder with compresed air, and watched the gauge for how quickly it goes down. if it goes down fast, you could have a burnt valve, a unseating valve, extremly worn rings, or a stuck ring, a bad vavle guide and so on.
Thread Starter
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New User
Joined: Aug 2000
Posts: 7
Likes: 0
From: Missouri
Could anyone tell me how a bad catalytic converter would affect the engine? Could it cause a misfire? I would figure if it caused a misfire it would be a code 300 or random instead of a single cylinder.
Thanks, I will look into finding someone to perform a leak down test, I can't figure out what else it could be. I pulled the conection to the fuel injector last night and it ran rough until the computer corrected for the abnormality. I tried this in the past for spark and it did the same thing (except it kept running rough with spark pulled). Reading these forums it seems that misfires frustrate many people.
Thanks, I will look into finding someone to perform a leak down test, I can't figure out what else it could be. I pulled the conection to the fuel injector last night and it ran rough until the computer corrected for the abnormality. I tried this in the past for spark and it did the same thing (except it kept running rough with spark pulled). Reading these forums it seems that misfires frustrate many people.
