having trouble finding misfire

**Spartanzz** · 02-19-2011

So, i have the P0303 code coming up. I have swapped wires to check that. The icm was replaced just before i got the car. I have swapped the coil with one of the others. I was told it may be the injector so today i switched the #3 with one of the others and i got my code reader and as of right now it has a pending code P0303 and thats with the coil and injectors swapper around. ALSO, the misfire only seems to be at idle because it doesnt stutter bog down and the only thing is it does make a slightly rough sound while as a red light or just sitting in gear, and when in park/gear you can hear the puffing out of the exhaust . I thought i may take the fuel rail off soon and try to see if something is clogged. Any other suggestions or ideas of what it could be?

**Seansta** · 02-19-2011

burnt valve, i would say.. whats the po303, is it a misfire? code fault?

**Spartanzz** · 02-20-2011

No p0303 is cylinder 3 misfire I just swapped the injectors today and I was also told something could be stuck in the fuel rail so may just take the rail off and clean it out. Because I'm really hoping I don't have to remove the head to fix it...

**Spartanzz** · 02-20-2011

Also, wouldn't a burnt valve be causing a misfire all the time? Or at least give the symptoms of a misfire like sputtering etc...cuz they the odd thing about this is even at wot there doesn't seem to be an lack of power.

**blueguy** · 02-20-2011

I'd go with flushing out the rail. Burnt valves aren't common and unless your running with literally no exhaust on the car...I'd doubt you'd burn a valve on these cars. After that...when you pulled the plug was it damaged at all ever? Bent or smashed? If so...then you've probably got a chipped piston. I know its at the extreme end of things...but you can always buy or rent a borescope and run it through the spark plug hole to examine the piston for damage. Are you modded at all?

**Spartanzz** · 02-20-2011

No all the plugs were fine. And the only real mod I have is an eBay intake cone filter and if it mattered autolite app104 plugs but the misfire was there before all that. And I just remembered this but before I ran some injection cleaner through and the code doesn't come up as often now but still comes up.

**fst4dr** · 02-20-2011

Have you checked the connector for the injector? if the pins are not making good contact it will cause a missfire condition. I had this on cyl #3 when I first got my car, took a bit to find it but finally found that the ground terminal was just not making a good connection. used a small pick and bent the tabs back down so they would press tighter on the pins of the injector and BAMM! problem solved!

**Spartanzz** · 02-20-2011

yeah ill check that out. Like i said earlier i swapped the injectors and when i did i decided to start the car up and disconnect the cylinder three injector just to see and when i did the engine RPm did change but the change was very small. So dont know if that changes anything.

**fst4dr** · 02-20-2011

yeah i swapped the injector with a spare one I had and it was still missfiring. but it was just that the terminal was making a bad connection

**Spartanzz** · 02-20-2011

Ah ok man ill have to give that a shot either later tonight or tomorrow cuz the cheaper the fix the happier i am

**Spartanzz** · 02-22-2011

Ok well I bent the pins in but no changes once I get paid tomorrow I'm going to get the tool I need to get the fuel rail disconnected so j can flush it out

**Spartanzz** · 02-24-2011

ok if anyone is still reading this i flushed the fuel rail out and still i have that misfire at idle... just yesterday my ICM went out so i replaced that as well as the o2 sensor and coil pack to that cylinder. So, at this point what could it be? I was told it could be a burnt valve but wouldn't that be a constant misfire? Once again any advice/help is greatly appreciated!

**blueguy** · 02-24-2011

Mmmmmmmm...I'd try and find someone with a borescope like I mentioned and check out the piston...see if something is damaged there.

**BillBoost37** · 02-24-2011

Swap the #3 and #6 plug wires on the coil. Does the miss move to #6?

**Spartanzz** · 02-24-2011

We tried that and no it doesn't. And I'm now pretty sure it can't be anything to do with spark and one big problem with it is its not constant enough to throw a code just a pending one unless I let it idle for a long time. But u can feel the misfire or at least a rough sound every now and then while at a light and like I said its not constant. We have now replaced the icm coil to 6 and 3 and all plugs only thing would be the word but it doesn't move when I switch them... and some goes for injectors

p.s. my friend just told me it could be the MAF. whats yalls opinion on that? i figured if it was the maf the misfire would be alot worse.

**Coolride** · 02-25-2011

You can tap on the Maf, and the engine will sputter if it's bad. I'd check the compression in no.3 against 1 or 5 since their easy to get at. Low compression will show it's head at low rpms..

**Coolride** · 02-25-2011

You can tap on the Maf, and the engine will sputter if it's bad. I'd check the compression in no.3 against 1 or 5 since their easy to get at. Low compression will show it's head at low rpms.. Maybe a broken insulator on the plug also, and you can't see it.

**DanGTP** · 02-25-2011

It's also possible a bad LIM gasket is letting coolant leak into cylinder #3. Has it ever been replaced?

**Spartanzz** · 02-25-2011

yeah when i got the GTP the lady said they LIM gaskets were changed and from what it looks like they do look good from what you can see form the outside. also the plugs are brand new. Ill try to tap on the maf and see if it does anything but yeah this is only at low RPM once you give it gas there is no stuttering or anything to show a misfire thats whats driving us nuts.

**FoSHO99** · 02-25-2011

Your running plugs colder than stock on a basically stock car as well? Whatd you gap them at? I would put in AL605's gapped at .045 to see if that helps. On heavily modified cars the 3800's are notorious for misfires at idle especially when running smaller gaps on the plugs, its just something we put up with.

You can also unplug the maf to see if it gets worse/better.