I have a 06 mustang GT I keep getting a cylinder 6 misfire. I replaced all 8 spark plugs and no change. Performed a relative compression test several time cold all cylinders passed at 100% compression. Back probed cyl 6 injector and coil circuits at the pcm. The test light was flashing bright and consistent while miss was occurring. Also preformed engine running compression test on cyl 6 found compression at 75 psi running and would intermittently drop 25 psi... What can I do to fix this problem?

 

i would swap the #5 and #6 COP's,
to see if the misfire moves to #5.

if it does, that would indicate a faulty
COP.

if the misfire doesn't move, that might
indicate an issue with the #6 injector.

 

i was getting eiratic misfire codes and i was getting a little blowby from s.charger

 

I'm guessing the cop as well.

 

I had the injector and coli swapped with another no change to CYL 6. I had all this work and the previous work done to it at a local ford dealer and they could not find out what was causing the misfire. The said they wanted to remove head to re-machine it what ever that means. But they wanted $4100 to do it, they said that they could not guaranty that that would fix the problem and that the next step after that would have to be a engine swap. That does not sound right to me. I take great care of my car and it only has 35000 miles so it’s not like it’s a really high mileage car. For $4100 I can buy aftermarket headers that are better than stock ones and they want to charge me that for just one cylinder head. Please help if you can.

 

ok bedaloca, to sum it all up, you have
replaced the following on cylinder #6.

spark plug
injector
COP

really that only leaves the PCM, the
wiring harness, or the cylinder head
itself (bad valve seal?).


not sure if seafoam would help or
not. hopefully someone else can advise
you on what you can test next.

 

how does the car drive?

 

Do a running engine compression test on the other cylinders. If they do not show a drop from 75 to 25 psi, then the #6 cyl. may have a sticking valve. Seafoam may help to free it.
(Note: It's recommended to do static compression testing after the engine has fully warmed up. Otherwise, inaccurate readings can result.)

 

The car for the most part is running good every now and then I feel it a bit sluggish when trying to pick up speed from a complete stop. Can anyone tell me what worst case scenario maybe.

 

Run a tank with Seafoam through the car and I'm guessing your problem will go away. Around 30-35k miles a bit of carbon residue starts to build up (hence the spark plug removal issues starting around this time) and the Seafoam should take care of that.

It would also help to know what modifications you have. Do you have a tuner? Forced induction?

Also, $4100 for aftermarket headers?? My header's weren't even $300.

I sure hope they meant heads and even that's ridiculous unless that includes labor.