crf538

I was at VIR this last monday and towards the end of the day i started noticing a little stumble at >5500 rpm

Its def not a dead cylinder like an ignition miss it just kinda stumbled a little and wasnt pulling like it should of been for the last few laps (felt mushy like it was pulling 10 degrees of timing)

CEL never came on and it idles and drives perfect at lower rpms

its an early 07 with 15k miles so im going to pull the valve covers and look around tonight, If no one has any other ideas ill hook up the wideband and log that and timing retard but its gonna be hard to really run it in the street like i was there

Any other ideas?

kamafnkazi

I had an issue like this on a forced induction car. It ended up being the spark plug gap being too large. Plugs might be a good place to start looking.

crf538

Thats funny I was specifically going to say it felt a little like a turbo car starting to blow the spark out.

i'll check the plugs too when i check the rockers.

Thanks!

C6z06man

Also could be wires/coils. I definitely would point towards the plugs first but it's still a possibility.

truckplay

I would pull the plugs and inspect them, I would also do a compression check while they are out and see if there is any one cylinder that is lower than the others, if there is you will need to dive in further.

whatcop?

Probably a burnt out plug

crf538

so the car came apart for new valves and i just got it back together. I didnt really think that would fix the problem but it needed to be done and it got plugs in the process..


same problem. I really dont think its an ignition problem, like its not a single miss it kind of just falls on its face. Stopped up cats (only 18k miles though) or a fuel pressure issue come to mind. are there any known problems with fuel supply that i dont know about?

any other ideas?

CanadaGrant

Is it possible you have a battery/charging problem and ignition is breaking down? Also, if you are runnung the stock intake/filter combo check to see if the stick on emissions pad inside the intake is starting to come loose.

crf538

Thanks ill check on that tonight..i feel like a partially blocked intake would have simular symptoms to what im seeing

Dirty Howie

Good call !!

I removed mine quite awhile ago. Was not easy.......


DH

wolf8218

Are you supposed to remove it or make sure it isn't loose?

crf538

so that wasn't it.. both pads are in tact. I need to log some passes with it but my laptop died the other day and I haven't gotten a new one yet.

any other ideas

thanks for all the help

Mark2009

OP, put it on a chassis dyno and data log the PCM. Should be quicker and ultimately cheaper than chasing parts

crf538

Yeah that's the plan I just gotta go buy a laptop. Maybe I'll go do that tonight

wolf8218

just don't buy a Mac

0Anthony @ LGMotorsports

Can you give us any details as to the modifications on the car?

This is what I would check and/or replace

• Cracked plug
• burnt plug wire
• bad coil
• low fuel pressure
• broken valve spring(s)
• bad ground, or loose ground connection
• Dirty MAF or bad MAF connection

I don't think it would be a plugged cat as they typically just loose power, not a cut out. I would almost think someone might have cracked a plug when they were working on the heads.

Dirty Howie

Why not, his (I assume PC) just died. I have had Macs since 1984 and never had one die


DH

Dirty Howie

I'm betting that this is great advise. I had a bad plug that caused all kinds of problems until it was found.


DH

crf538

The car is bone stock except for the new valves. I installed the heads, But the problem started before before the heads came off. So its not that.

Its not a miss like a plug or coil....it kind of falls on its face I'm thinking maybe its a fuel pressure problem but if never seen anything stock run out of fuel like that..

I have seen a voltage problem cause a pretty bad lean condition..but again not on a stock vehicle....I've also seen bad convertor have similar symptoms but with 18k miles I can't imagine that's a problem...it also isn't ratteling like the convertors comming apart

Thanks for all the help guys

crf538

Yeah I'd agree..but its the same with new plugs...it actually seems to be getting worse....
And HP tuners won't run on that Mac lol...I need to go buy a computer and stop guessing