Misfire on WOT over 5k Rpm

[WheelStander]

I am exeperiencing what seems to be a slight misfire only over 5k rpm and only on WOT.

I have had an uneven idle, fluctuates between 824 and 874 pretty steadily for the past 3k miles or so.

No codes and plugs have 15k over the past 2 years.

Cops are original with 110k of total beatdown miles by me.

Looks like one of the Cops has some scorching or burn type marks on the top from visual inspection.

I am thinking that this is electrical and am going to pull my Cops and have them tested at a friends shop, replace the plugs and alternator.

Never used the Cops tester before, how reliable is that device and what if it does not detect an issue with any Cop?

Anything I am missing here?

Thanks for any input.

2003 Stock Cobra,, Kenne Bell SC

 

[b_dike]

What about your plugs/ plug gaps. Could it also be spark blow out?

 

[WheelStander]

Plugs were good for about 10k miles but after that is when the uneven idle started but WOT was still good. Maybe NGK plugs are a little out of gap now?

WOT issue started about 100 miles ago, if that helps.

Thanks for posting.

 

[Bdubbs]

I'd check cop's first then frps.

 

[WheelStander]

Thanks guys for the replies. Had not considered the frps, will check that as well...

'You can check the resistance of the two circuits in the FRPS with a multimeter. I don't remember the spec'd value ranges off the top of my head, but they'll turn up in a search.'

 

[Bdubbs]

Thanks guys for the replies. Had not considered the frps, will check that as well...

'You can check the resistance of the two circuits in the FRPS with a multimeter. I don't remember the spec'd value ranges off the top of my head, but they'll turn up in a search.'

Yeah the frps can fail mechanically and electrically. Still wouldn't hurt to look at plugs either and maybe just change them. Keep us posted.

 

[cj428mach]

What is your AFR during this time? I'd suggest pulling timing with your handheld while you're trying to determine where the problem is. You could be running lean.

 

[WheelStander]

Good point...I only got on it once or twice, I'll check that tomorrow...afr did look fine and fuel pressure looked,fine as well.

Thanks.

 

[WheelStander]

Sorry guys, I pulled my plugs, they looked like they burned perfectly but we're way out of gap.

Replaced em and am now seeing full hp again.

Thanks for posting.

 

[b_dike]

No prob, glad you got it figured out. What were your plugs gapped at before you changed them?

 

[WheelStander]

I still have em I think, I'll check for kicks and to know when spark blow out starts to happen, because that's what was happening but I did not realize until posted above.

034 I think or more.

 

[WheelStander]

All were 034 and greater, I was experiencing some spark blow out for some time but just thought it was my Magnapacks making the car sound like crap.

Had the car out to CMS for a private party last night. Had to drive all over to pick up my girl but car is running great now and I am back at my peak hp, actually hit some numbers a little higher than my previous peak on a pull.