Misfire and no code

[MYSTCHRM]

History: Month and a half ago I, I go WOT and the tone of my exhaust got deep and it seemed almost as if the traction control had come on. No tract. ctrl light so it couldn't be that. I'm thinking a misfire, but no codes are thrown.

Having a friend that had the same issue on his '99 and it turned out to be a coil pac. So, I go out and go to Ford and they tell me that I've a misfire on #8. I replace all the COP's with Gran. (there is another post on that, lets not go there!). The issue goes away, for a week.

Now I replace the stock plugs with stock plugs and the fuel filter. Given plety of feedback to lower the gap, I bring the gap down to 37. Problem goes away, for four weeks.

The problem has returned except I get the misfire at idle, take off, and WOT. I bring the car to a local shop and we do a compression test. Everthing seems fine. They want to see if it is the plugs. In go TR6's. Take it out for a drive, WOT and I've got the misfire. At idle, you can hear the misfire although not as bad.

The Net: I've got a misfire but not throwing a code. Not sure which cyl. right now. Replaced COP and orginal plugs at 55K miles and plugs again at 56.5K miles. Replaced fuel filter and PCV. Car has SLP LM catback, SLP Xpipe, K&N CAI. Never had a tune and never changed the pulley.

Possibilities:

I'm thinking it can't be the cats as I wouldn't get the misfire at idle.
Can't be the plugs.
Highly doubt it is the COP.
Not the fuel filter or PCV.

Clogged fuel inj?
Electrical short somewhere?
Water in vacum line? (I know, I'm stretching it)
Dirty crank sensor?

This has me frustrated because I can't seem to find anyone on the site with this problem on their 03/04 Cobra and found the cause. Let the experts offer some insight!

 

[Red Shift]

ttt

 

[TrickStang37]

sounds like it could be a vacuum leak.

maybe your EGR getting stuck open?

do these cars have an ignition module of some sort?

have you tried datalogging?

 

[MYSTCHRM]

I can't datalog as I don't have a device.

Sorry I haven't gotten back to this in a bit. Here is what has been done since I last posted.

I've replaced the fuel pressure sensor. That didn't do it. I've swapped injectors, that didn't do it. I've swapped the MAF and that didn't do it. I'm still not getting any codes thrown.

I'm at a total loss. I'll take a look at the EGR. This can get you to the point of just wanting to sell the damn thing.

 

[Tobias]

Stop throwing parts at it, it will only worsen your frustration.
I think it is time for you to perform a leakdown test. If the dealer sez your problem was cylinder #8, It could be a valve sticking or a broken valve spring. You have changed every variable except for base engine parts. With your loud exhaust it would be very difficult to hear a valve train noise.

 

[MYSTCHRM]

Trust me, I don't have the money to throw parts at it. I have an appointment next Friday at a local shop. I'll talk to them about the leakdown test and go from there. I'm at the point of just dropping it off at Ford and breaking the piggy bank to let them drain me of my last .02

 

[redfr03svtsnake]

i fought a problem with the same symptoms you are describing for 2 months, found out it was just the spark plug gap, as you have already been told, but try bringing the gap down to .035-.032 (somewhere in that range) depending on the boost you are seeing....... just try........

 

[JL1968]

I feel for you and in the same boat. I did the spar plugs, fuel filter and o2, just went out. No spark plug wire issues either, and I gapped the new NGKs at 42 since says 42 to 46. I guess i can try tolower gaps more like you said. I might try to replace EGR since that was brought up too. Let me know how yours goes 809.

Jesse

 

[Red Shift]

My problem was a dirty MAF.

 

[mavereq]

any updates?

 

[Juruense]

Could it be the FRPS?