Misfire on cylinder 7

[Hacklemerc]

Alrighty then, some of you are aware of the problems I have been having with the wifes car. Well it has started again. I started the car this morning and noticed it was idling really bad again. When you hit the gas the car goes just fine but slowing to a stop it starts idling really rough and seems to want to die. After about 15 minutes of driving the check engine light comes one. Take it up to Autozone and thier little code reader says its misfiring on Cylinder 7.
The last time this happened I changed out the coil, and plug and it ran great until now. I'm going to try the same thing but I am at a loss as to why it keeps doing this...
Any help would be appreciated.

Hack

[Blackmobile]

I find it hard to believe that just 7 is misfiring over cylinder 8. IMHO it would be reasonable that both 7 & 8 are your problem.

[Hacklemerc]

I'm at a loss. Short of taking it to the stealership and having them look at it I don't know.

[RF Overlord]

Swap the coil with any other cylinder and see if the problem follows.

[Hacklemerc]

Well I took it to the Stealership. The diagnosis so far is that I have about half the compression that it should have on the #7 cylinder. The Service manager said this could be a number of things, from a bad spring, to a bad valve, or a bad ring on the piston, or a bad cam lobe. Well there goes Christmas.....

[Glenn]

I have never heard of low compression causing a mis-fire code - rough idle yes. If it threw a mis-fire code then it electrically mis-fired. I would not proceed with the dealer until I took the MM to a local garage and get their opinion. Do not tell them what the dealership said.

Glenn

[Hacklemerc]

Ordinarily I do not trust the Dealerships either. But the wife has been going to the same Dealership for about 7 years now with several different cars and she trusts them. They have performed all the scehduled mainenence on the car and any extra work on it as well.

I wasn't clear in my earlier post. The reader said it had "detected" a misfire in the last 1000 revs, but did give a different error code. The code (if I remember correctly) was p016.

[CanadaMarauder]

The 4.6L is known to have cooling problems in Cylinder 7 and 8 Causing Burnt valves which will flag a mis-fire codes..Might want to have someone do a cylinder leakdown test to see if 7 valve is burnt

[03mmmonroe]

I would also hope the dealer stress tested the coils to make sure they were working. Having the cylinder compression checked and leak down could also help with finding your concern. I have had 3 coils replaced on my 03 and I just rolled 54k. Good luck.

[Marauderjack]

The 4.6L is known to have cooling problems in Cylinder 7 and 8 Causing Burnt valves which will flag a mis-fire codes..Might want to have someone do a cylinder leakdown test to see if 7 valve is burnt

There have been a lot of discussions about this and it is still not proven....I have 207+K miles on my motor with 123K supercharged and still running strong without additional #7 & #8 cooling!!:shake:

Try another coil and see what happens...I have a spare if you want it!!:beer:

[Hacklemerc]

The 4.6L is known to have cooling problems in Cylinder 7 and 8 Causing Burnt valves which will flag a mis-fire codes..Might want to have someone do a cylinder leakdown test to see if 7 valve is burnt

The leakdown test is done and it appears that some of the valves are in fact burnt. We are in the process of calling the Warranty company to see if this is covered, or even if we are still in warranty. The dealer is recomending pulling both heads and sending them out to a machine shop. My day just took a crap. I'll be working a bunch of overtime to pay for this....

[fastblackmerc]

The leakdown test is done and it appears that some of the valves are in fact burnt. We are in the process of calling the Warranty company to see if this is covered, or even if we are still in warranty. The dealer is recomending pulling both heads and sending them out to a machine shop. My day just took a crap. I'll be working a bunch of overtime to pay for this....

No extended warranty?

[Hacklemerc]

Nope expired at 100k miles. She has 114 k on it. The estimated repair cost is about $3500 depending on what they find when they take the heads off.