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-   -   Misfire ONLY at idle problem (http://www.jeepforum.com/forum/f19/misfire-only-idle-problem-1371256/)

chero123 05-20-2012 02:41 PM

Misfire ONLY at idle problem
 
I have a 2004 Jeep GC 4.0 and it has a few problems: one is that the oil gauge goes to zero when engine is warm and at idle. I already replaced the oil pressure sensor (dealer) and still doing it. I will check the pressure with a mechanical gauge, I am suspecting that the pressure is indeed low... But the more puzzling problem: I get a misfire ONLY AT IDLE on cyl 5. Swapped injector from another cylinder, replaced the coil, plugs, problem stays on cyl 5 all the time. Only at idle, if I hit the gas it drives perfect. Injector works when the misfire happens (I can hear it clicking with stethoscope). Tried to find a vacuum leak, found nothing. This is not the typical Jeep heat soak problem, it does it right after I start the cold engine, as soon as the RPMs drop to 700. Basically, not much heat under the hood at all...
This is a new vehicle to me, don't know what happened to it before. Any ideas?

MrElPoderozo 05-20-2012 05:58 PM

I am not familiar with that engine but can you SWAP the spark plug WIRE for another one and see if the problem goes away or if you swap the wires from another cylinder for the one in #5(MARK THE WIRE ON CYLINDER #5) and see if it moves to where the bad wire is(THE MISS FIRE). Sounds like it could be a bad spark plug wire or a bad connection on the Distributor also check the Rotor connection on the cap for cylinder #5. Sometimes when we make are own wires and we put the connection through the boot it gets disconnected from the crimping. you say that it runs good when you drive it and I think its because when you are driving it it creates more spark and is enough to run good. I don't know how many miles on the engine but the low oil pressure could be a bad oil pump,wrong viscosity, or the bearings might be worn out. I am no expert but I try to help,I hope that this will help you,good luck to you.

chero123 05-20-2012 08:36 PM

No wires on this engine, has a coil pack for all 6 cylinders.

hillbilly07 05-20-2012 08:59 PM

I have a 2007 wrangler x and I am having some major problems with It ...... I fueled up and as soon as I went to start it it would only turn over. I pushed it in to a parking spot and tried again but it would do anything not turn over or anything the Lights and instrument panel lights would turn on and that was about it. I tried jumping the starter And all it would do is turn over. I need some help here please

MrElPoderozo 05-20-2012 10:21 PM

Quote:

Originally Posted by chero123 (Post 13599039)
No wires on this engine, has a coil pack for all 6 cylinders.

Sorry! Did you checked the timing? and the cam sensor? or crank sensor? I would check those things next ORRRRR!!! sense you can drive it take it to AUTO ZONE or Advance Auto parts and have them put the scanner for ((FREE)) LOL, before taking it to a mechanic,good luck to you.

MrElPoderozo 05-20-2012 10:44 PM

Quote:

Originally Posted by hillbilly07 (Post 13599135)
I have a 2007 wrangler x and I am having some major problems with It ...... I fueled up and as soon as I went to start it it would only turn over. I pushed it in to a parking spot and tried again but it would do anything not turn over or anything the Lights and instrument panel lights would turn on and that was about it. I tried jumping the starter And all it would do is turn over. I need some help here please

Sound like fuel pump problem to me,if you turn the switch to the ON position and you cant hear the fuel pump RUNNING then that could be your problem. Usually fuel pumps don't give warnings when they go out on you except they get louder but not to many people notice that. I would also look into the fuse box for broken fuses (CHECK YOUR MANUAL). The bad part about this is that it could be soooooo many things wrong that its hard to know without actually looking at the car, but if I was in your shoes I would check the fuel pump,fuses and see what the Manual says about overfilling the tank sometime they put some sorta check valve and some bull %$#@ that makes thing complicated and take it from there,I wish you luck with this project.

chero123 05-21-2012 07:45 AM

I checked to code on my Jeep, it's misfire on cyl 5.

obfdcherokee 05-21-2012 04:56 PM

Quote:

Originally Posted by chero123
I checked to code on my Jeep, it's misfire on cyl 5.

Your misfire sounds like a valve problem. At idle the valve isn't closing all the way. This cause compression loss and blows the fuel right out the tail pipe. It quits off idle because it's moving faster and not as noticeable. You probably have carbon build up or a weak valve spring. do a compression test and compare 5 to the others. As for the oil pressure probably oil pump or main bearing wear. Hope this helps

bprks55 05-21-2012 04:58 PM

Possible Intake Gasket, At higher RPMs. It won't show up

obfdcherokee 05-21-2012 05:25 PM

Quote:

Originally Posted by bprks55
Possible Intake Gasket, At higher RPMs. It won't show up

Yeah but massive vac leak would occur

chero123 05-22-2012 08:12 AM

I suspected a vacuum leak/intake gasket too, but I could not get the idle to change at all when spraying carb cleaner around #5. Usually a big vaccum leak that will result in a misfire would be very evident, most of the time I can even hear it. Unless it leaks somewhere inside the manifold, like exhaust leaking inside the intake?!
The compression sounds the most probable based on all the tests so far, but when I crank the engine without starting, it sounds like it has good compression on all 6 cylinders. I will try to get a compression reading today, and put a number in place of "sounds good". But I suspect the compression is going to come back good.

hillbilly07 05-22-2012 08:23 AM

Quote:

Originally Posted by MrElPoderozo

Sound like fuel pump problem to me,if you turn the switch to the ON position and you cant hear the fuel pump RUNNING then that could be your problem. Usually fuel pumps don't give warnings when they go out on you except they get louder but not to many people notice that. I would also look into the fuse box for broken fuses (CHECK YOUR MANUAL). The bad part about this is that it could be soooooo many things wrong that its hard to know without actually looking at the car, but if I was in your shoes I would check the fuel pump,fuses and see what the Manual says about overfilling the tank sometime they put some sorta check valve and some bull %$#@ that makes thing complicated and take it from there,I wish you luck with this project.

Well I got it in the shop in just wait waitin on the prognosis.....do you think a run relay fuse could cause all of this?

MrElPoderozo 05-25-2012 11:12 PM

yes ,I think a broken fuse can cause that and more. cars now days have one fuse for more then one thing at the time, like wipers would not work if you remove the fuse from the hazardous lights etc... I hope that you got the problem fixed at the shop and that you are ok now,sorry I was not much of a help to you,good luck to you ok.

chero123 05-30-2012 07:53 AM

I finally got around to measure the compression, all cylinders show perfect compression. I am still thinking a vacuum leak, or most likely a crack in the head between exhaust on #4 or #5 and intake on #5. I will post my findings if I ever get to fix it.


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