[Leanz]

My 2000 v6 auto mustang with 67k miles is misfiring from what looks like oil burning in the 6th cylinder. When I did a tune up, the 6th cylinder spark plug was oil fouled and looked like it hadn't been firing in quite a while. I changed all of the plugs, did the tune up, checked my coil and ran seafoam through it and it solved my problem for a little while (maybe 30 miles or so) then the misfire/sparkknock returned. I pulled the 6th cyl. plug and it didnt look like it had been misfiring. Anyways. I have done the valve cover fix, that didnt do a damn thing - its still sucking up some oil through the pcv valve. I have checked the compression and all of the cylinders were around 115; so thats fine. I need some help here. People have thrown random ideas at me on other mustang forums of what could be wrong, but some of them are sooo off the wall, I didnt try many of them. Please help. I am so damn frustrated with this stupid car. I can only notice the misfire at idle, and its not every single time, its like it fires correctly 30 times then misfires 5 times, jsut enough for me to feel a shudder, then its back to idling normally for a few seconds. the idle never drops, it just misses.

halp

[wraitherx]

so you are throwing no codes at all?

[Leanz]

no. no codes. not a one.

[Leanz]

bump

[stephen]

Compression of 115 sounds quite low for 67K miles. You might try putting some oil in the cylinders and see if the compression comes up. If it comes up a lot, it's rings. I would expect compression of at least 150.

[stephen]

Cylinders #3 and #6 are the ones that get messed up by the PCV system. It could be crud
on the valves.

[Leanz]

So about the valves. How do I clean them? Should I just delete the PCV and put a breather on? and put a screw in the line leading to the intake?

[stephen]

I wouldn't delete the PCV.

If there is low compression then you probably need a valve job, which requires removing the cylinder heads. I would suggest getting a professional evaluation before doing that.

[Leanz]

why wouldnt you delete the pcv and put a beather on?

and I dont think my compression is low

[stephen]

I wouldn't delete the PCV since it is part of the emission system. If you leave it open then the oil fumes and blow by are being vented to the atmosphere. Don't know about emission laws in your state.

Most engines will have compression readings in the range of 150-170 psi.

If the plug in #6 got oil fouled it is likely that there is some kind of oil control problem. It could be as simple as a cracked stem seal. I haven't had this problem due to the PCV system, though it does build up carbon in cylinders #3 and #6.

[Leanz]

Yes, it builds up carbon due to burned oil, due to the PCV line running to the intake right to cylinder 6. (I only have one PCV, so it only affects my cyl 6). Whenever I pull my pcv out, it is covered in oil and sometimes the oil drips right out of it. I am pretty convinced that is the culprit of the oil that is fouling out my plug.

and I cant beleive I did this, but I meant 165 psi not 120!! heres proof haha Oil Soaked Spark Plug, Perfect Compression?? - Ford Mustang Forums

an older post of mine - as you can see I did the compression test a while ago and am still trying to figure out what the hell is wrong.

[stephen]

165 psi is fine, which means the valves and rings are OK.

I found that both back cylinders build up excess carbon and that can lead to pinging. Even had a damaged plug on #3 due to detonation. A valve job and cleaning all the carbon off the tops of the pistons fixed that. I believe there are products you can get from Ford to remove carbon.

Since the plug wasn't oil fouled this time, perhaps something else is causing the misfire, like a bad wire. Check all the plugs for bridging deposits, especially if it is misfiring under load.