Misfire all cylinders after header leak fix....WTF?

[WickedSS2005]

I had a small leak near my #4 primary on my header top far driver side bolt. Got together with a buddy and we went thru each bolt 1 by 1 to find it. Great, no more leak..... BUT! Now I have a sporadic idle and misfires in all four cylinders. :cussing: It'll start up, idle high, come down to the normal 850 range, then bounce around, almost stall and then shoot really high. I just replaced my O2 sensor last summer before my warranty expired, but that is the only thing I can think of. HPT scans show my O2 B1S1 as a flat line, then a jump high, then a dive low, long flat line, repeat as opposed to the normal peak and valley rhythm. My low end timing is running 20-25* when the tune is commanding teens and nothing on the tune has changed, even reflashed it to be safe. I'm tired of fucking with the car today, but anyone have any other ideas before buying my 4th 02 sensor? It's just ironic how I fix my leak and now I have this.

If it's not one thing it's another with this car lately. :cussing: :cussing: :cussing:

I cleaned my tb today, disconnected the battery over night, and checked my plugs, all is good. :sigh: WTF!

[WickedSS2005]

BUMP!! I'm lost here guys

[Tennpenn83]

Originally Posted by WickedSS2005

I had a small leak near my #4 primary on my header top far driver side bolt. Got together with a buddy and we went thru each bolt 1 by 1 to find it. Great, no more leak..... BUT! Now I have a sporadic idle and misfires in all four cylinders. :cussing: It'll start up, idle high, come down to the normal 850 range, then bounce around, almost stall and then shoot really high. I just replaced my O2 sensor last summer before my warranty expired, but that is the only thing I can think of. HPT scans show my O2 B1S1 as a flat line, then a jump high, then a dive low, long flat line, repeat as opposed to the normal peak and valley rhythm. My low end timing is running 20-25* when the tune is commanding teens and nothing on the tune has changed, even reflashed it to be safe. I'm tired of fucking with the car today, but anyone have any other ideas before buying my 4th 02 sensor? It's just ironic how I fix my leak and now I have this.

If it's not one thing it's another with this car lately. :cussing: :cussing: :cussing:

I cleaned my tb today, disconnected the battery over night, and checked my plugs, all is good. :sigh: WTF!

that is kinda crazy how a header leak being fixed will cause misfire. idk man, we only took off the header bolts and the vacuum line for the valve cover. you said you checked the plugs, any other changes AT ALL in the last week? how about the week before the header leak fix?

[Ahriman]

i dont think fixing the header caused your misfire... it was probably always there, but you couldnt feel it as strong with the leak. I have always had an idle misfire, and when my flexpipe was torn and i had a HUGE exhaust leak, i could barely feel my misfire anymore. as soon as i fixed it, it was back to normal though. dont know why, just sharing the info.

[WickedSS2005]

No changes in the past 2 months other than the exhaust. It fuckin idles all over the place and when I come to a stop it'll idle at 1800rpm then when I hit 0mph goes down to 850. Then it starts it's bouncing all over again. My idle is fubar'd up BAD and I don't know why. My tune (has been on the car for 2.5 months) was near flawless and has run strong as hell (still pulls like a bitch) but something, somewhere is wrong..... I'm firmly set on it being mechanical/physical not tune

[Ahriman]

Originally Posted by WickedSS2005

No changes in the past 2 months other than the exhaust. It fuckin idles all over the place and when I come to a stop it'll idle at 1800rpm then when I hit 0mph goes down to 850. Then it starts it's bouncing all over again. My idle is fubar'd up BAD and I don't know why. My tune (has been on the car for 2.5 months) was near flawless and has run strong as hell (still pulls like a bitch) but something, somewhere is wrong..... I'm firmly set on it being mechanical/physical not tune

i would look elswhere than your exhaust... i cant see that being the cause.

[crazybrew609]

check compression yet?... what about your fuel delivery?..

remeber 3 things cause your car to work right

ignition- pcm, plugs, coils, tune
fuel - pcm, injectors, fuel filter, fuel pump
air - pcm, tb

normally the air portion is pretty easy and not really the problem, not mabbey the tune might have a tweak but if it's been on for 2 months i doubt thats your problem, your fuel could deff be an issue i mean we do have really shitty gas and if you don't use 93 your car runs like shit, plus you gotta remeber we just started to get hit with the 10% bullshit gas so tweaking back your tune a couple degrees might not be bad, also looking into mabey changing the fuel filter and pulling to fuel rail and filters to check for any clogs in there would be a good idea, you never know if could be bad gas from 1 place that just so happened to be when you did the header and now your fuel pump is clogged or something, i see that quite often at the dealerships. now as for igntion i would say if you know the tune is good it's prolly not that and you said the plugs look fine so thats not either, mabey re-gap the plugs just to be safe and go from there, honestly i would say drop your gas tank and check the fuel pump screen and the gas in the tank. you might have gotten some shit gas and now your cars hating life

just my 2 cents


oh also check compression just to be safe

[billabong9687]

my thought exactly, I'm actually going to his place tonight to change his fuel filter, the car has 42k on it and never had a new f.f put on, after that I'd like to do a leak down test, I was gonna say maybe a burnt valve, but doubtful on all four cylinders. That's what makes me believe it's a fuel problem, being that is the only thing that they share.

[crazybrew609]

i hope i'm right or atleast in the ball park,, i love being right when i diagnose cars over the internet

[Italianjoe1]

Sounds like an air leak. Check all your vac lines and TB connections and such. That will cause the high idle on coast-down and the other misfire issues and such.

Change the fuel filter as well if it has over 30K on it.