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Random Misfire

 
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Old 23 Dec 2012, 10:29 pm
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Join Date: Jun 2011
Location: West Virginia
Posts: 10
Default Random Misfire

This all started back in August when I was driving up a mountain going to college. The check engine light started flashing for about 5 seconds, then it would go off and it repeated this two or three times then it finally just stayed on. I took it to the garage the next day and they told me I had oil leaking into the spark plugs and that I would need new spark plugs, ignition coil, and seals on the head gasket. I believed them because a month before hand I replaced my spark plugs and noticed a little oil but just ignored it. Two weeks later as I was driving home it did the same thing came on and flashed. Took it back to the garage they told me it was the wires so they replaced the spark plugs and wires this time. About two weeks later it did the same thing again. I took it back and they told me it was the computer and the dealer would have to reprogram it. I took it to the dealer. They told me it was probably the fuel pump but they couldn't test it because they didn't have the tool. I went ahead and replaced it myself about week later when I went home. On my way back to college the light came on again and did the same thing. I took it to a different dealer two weeks later and they downloaded the info and sent it to Chrysler for further diagnostic or something, but while they had the car they replaced the vacuum hoses and spark plugs. When they got the info back from Chrysler they said the engine need to be decarboned but I didn't have the money to do that so I just used some seafoam. After the seafoam the light still comes on and now I am stumped on what to do next. It is a 2001 with the 2.4L non-turbo and has 168k miles.

This is everything I have replaced so far: crankshaft position sensor, camshaft position sensor, fuel pump, pcv valve, pcm, radiator fan, spark plugs and wires, ignition coil, vacuum hoses, headgasket seals.

Any input would be appreciated.
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Old 24 Dec 2012, 12:31 am
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Join Date: May 2012
Posts: 1,354
Default Re: Random Misfire

Quote:
Originally Posted by senji View Post
This all started back in August when I was driving up a mountain going to college. The check engine light started flashing for about 5 seconds, then it would go off and it repeated this two or three times then it finally just stayed on. I took it to the garage the next day and they told me I had oil leaking into the spark plugs and that I would need new spark plugs, ignition coil, and seals on the head gasket. I believed them because a month before hand I replaced my spark plugs and noticed a little oil but just ignored it. Two weeks later as I was driving home it did the same thing came on and flashed. Took it back to the garage they told me it was the wires so they replaced the spark plugs and wires this time. About two weeks later it did the same thing again. I took it back and they told me it was the computer and the dealer would have to reprogram it. I took it to the dealer. They told me it was probably the fuel pump but they couldn't test it because they didn't have the tool. I went ahead and replaced it myself about week later when I went home. On my way back to college the light came on again and did the same thing. I took it to a different dealer two weeks later and they downloaded the info and sent it to Chrysler for further diagnostic or something, but while they had the car they replaced the vacuum hoses and spark plugs. When they got the info back from Chrysler they said the engine need to be decarboned but I didn't have the money to do that so I just used some seafoam. After the seafoam the light still comes on and now I am stumped on what to do next. It is a 2001 with the 2.4L non-turbo and has 168k miles.

This is everything I have replaced so far: crankshaft position sensor, camshaft position sensor, fuel pump, pcv valve, pcm, radiator fan, spark plugs and wires, ignition coil, vacuum hoses, headgasket seals.

Any input would be appreciated.
had a neon that did this exact same thing. Your fuel injectors are shot :-D they will cause random misfires all over the place and cost you thousands in parts ya didnt need. Have the fuel pressure tested under load. I can almost 100% guarantee its the injectors :-)
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Old 24 Dec 2012, 02:45 pm
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Join Date: Jun 2011
Location: West Virginia
Posts: 10
Default Re: Random Misfire

Quote:
Originally Posted by pluminator View Post
had a neon that did this exact same thing. Your fuel injectors are shot :-D they will cause random misfires all over the place and cost you thousands in parts ya didnt need. Have the fuel pressure tested under load. I can almost 100% guarantee its the injectors :-)
Iv'e been thinking it could be the fuel injectors. I haven't replaced them yet because I just thought it was a little weird that all four would fail or get clogged at the exact same time. How do you do the test while it's under a load? Do I hook the gauge up somehow so I can see it while I am driving?
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Old 24 Dec 2012, 04:00 pm
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Join Date: Sep 2001
Posts: 27,750
Default Re: Random Misfire

To test the fuel pressure itself, you have a Schreoder valve at the end of the fuel line (see picture). Also, most garages can run fuel injection cleaner under pressure directly to the injectors while it's running to give them a good cleaning.

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Old 24 Dec 2012, 06:35 pm
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Join Date: May 2012
Posts: 1,354
Default Re: Random Misfire

Quote:
Originally Posted by senji View Post
Iv'e been thinking it could be the fuel injectors. I haven't replaced them yet because I just thought it was a little weird that all four would fail or get clogged at the exact same time. How do you do the test while it's under a load? Do I hook the gauge up somehow so I can see it while I am driving?
They wont all fail at once, 1 single clogged injector or failed injector can cause misfires and a slue of other codes to pop up, it messes with the fuel/air mixture, ox sensors etc. It could be just one, or they could all have the same amount of gunk in them and just be feeding badly.

The r valve as cruzin said is on the side of the fuel rail that the injectors are plugged into.

How they test it under load is by hooking a PSI gauge up to the valve, then running the engine. *provided they can get it to fire up* that way they can see the fuel pressure when the pump turns on *accessory* and also the pressure when its in Neutral and they rev it up. IF it is at normal PSI before they run it, then the PSI increases or drops under load, it shows that the injectors are toast, or one of them anyway
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