Help diagnose my ignition problem! [Archive] - Forum


View Full Version : Help diagnose my ignition problem!

06-15-2008, 08:23 AM
My car has been acting up lately with a bad misfire at idle and WOT. When going WOT, the engine will misfire and just bounce off of 5k rpms. I thought it was a transmission problem because it happened when the car would downshift, but it will do the same thing in park or nuetral as well, and is clearly a misfire not the rev limiter. Also, it has a random misfire at idle, but doesnt throw any codes.

There are a few things that I have tried with no success. I repaired some wires that melted against my headers, going to the crank sensor, tryed swapping out coil packs and ICM which just made the misfire TERRIBLE, checked all my plugs and wires, and Ive performed a case learn as well.

The idle misfire has been happening for a long time, but unfortunately I dont remember when exactly.

My guess at this point is that the reluctor wheel on the crank is bent, throwing off the timing just ever so slightly. I could have damaged it when swapping crank pullies. Also there is a small oil leak there that could have damaged the sensor.

Any help is appreciated.

06-15-2008, 08:25 PM

06-16-2008, 06:05 AM
Sorry for the extreme bumping, but Id like to get this fixed before the midwest meet on friday. Its a lot more fun to race than it is to watch

06-16-2008, 07:42 AM
Can you check to see if drive cycles are completed first. Then check for pending codes. Check for air leaks during cold start-up. Could be a partial clog in teh injector, but then you could get codes.

06-16-2008, 02:20 PM
No codes are showing up, it just idles like crap and the misfire at WOT. Ive got a set of trailblazer injectors Im going to swap in today. The fuel filter has never been changed either. I hate just throwing parts at it, but they will get put on the car eventually anyways.

06-16-2008, 03:20 PM
think maybe yu neeed new spark plugs?...when mine were goin bad at one point it would miss very bad at w.o.t i can remember tho if the idle had slight fluctuations tho

06-16-2008, 08:38 PM
think maybe yu neeed new spark plugs?...when mine were goin bad at one point it would miss very bad at w.o.t i can remember tho if the idle had slight fluctuations tho

I just put in new plugs about 500 miles ago, but I should pull them out and check all of the gaps, as well as pick up some better wires.

I swapped to the trailblazer injectors today since I had nothing better to do and theyve been sitting in my room for a while. They didnt help any, but didnt hurt either. The car definitely needs to be tuned again though.

06-17-2008, 05:53 AM
Im still stumped as to what my problem is with this misfire. I couldnt get the car to misfire at WOT yesterday, which is good, but the idle is bad still.

Anyone have problems running NGK TR6 plugs? Theyre colder than stock, because im on the bottle. The gaps are pretty tight on them right now, so I can try opening them up to stock gaps again, maybe even pick up some stock plugs to see if that helps.

06-17-2008, 05:56 AM
thats what ive got on my car...ive had no probs with them

02-04-2015, 08:57 AM
Bringing thus thread back from the dead, because I'm experiencing similar problems. The car starts, idles and runs just perfect, it's just when I WOT, that it seems to misfire/pop and Rpm jumps back and forth like crazy.
Recently work done:
Oil change, iridium spark plugs, and msd wires
Any ideas? Thanks in advance

02-04-2015, 09:38 PM
make sure the plug isn't cracked. you have to be VERY careful with those, I've heard and read horror stories about even though they're pre-gapped, someone would move it, and crack the electrode, and whoopsie-daisy!

if you have your old ones (i know, nobody keeps them) toss them back in, or just 1 of them, replace each plug 1 by 1 until you find the bad one.

and if that doesn't do it, try those wires.

if it's doing it from an oil change, you need a young priest and an old priest, and some holy water

sugar ray
02-08-2015, 10:56 PM
Wow!! Toughy!! Just curious if you've verified your cat is ok?? Almost sounds like it could be a "partially" failed plugged cat? My 02 SE's cat failed prematurely and car acted this way with very low miles. It was only later that I found out the classic LIM issue with the 3.4's is what caused my cat to plug. I've also seen a brutally plugged air filter cause this condition at WOT. Starving for air causing the computer to over compensate. Bad MAF can cause this as well and not show any codes. Sounds like you've covered all bases regarding spark. Could be a mixture gremlin. May also want to verify fuel pressure

02-08-2015, 11:36 PM
My cat was recently replaced with the HF cat that comes this the MMS DP set up. I haven't even had time to look into this problem, but I've noticed it only does it during hard acceleration while trying to down shift or just change to a higher gear under decent stress (3500+rpm). Also it was not doing it before the tune up, I made sure all plugs were gapped properly, only thing is with these MSD wires , not all of them made that "click" noise while plugging them in, like if the wire was too long to plug into the plug, that's the first thing I wanna check, some of them clicked, some of them didnt, so I just tried to push them in as far in as possible without causing any damage of course...

Edit:forgot to mention, car sometimes randomly dies, very rare, but it does, don't know if is somehow related, or its just because one of my terminals is missing and there's just a screw in place, it has been there since I remember so I don't think it would start causing a problem just about now.