General Maintenance & Repairs - Misfire After Warm ...Help!!

ok so ive been chasing this problem for a couple weeks now. i need a little help figuring it out.

i have a 01 ss. if i start it cold it will not miss and run very smooth, after it warms up it starts to have a random misfire. not bad but i can feel it. it does not hesitate when driving and you can only tell below 1000 rpm. i put a scanner on it, and it does not show any codes. i guess the misfire is not bad enough? now here are the things ive tried. ive changed front o2s, fuel filter, swapped all the coils with ones that i know work, spark plugs an wires,cleaned maf, new air filter. ran injector cleaner threw it multiple times no change. tried running with maf unpluged no change in misfire. now like i said car runs great just misfire at idle.im still getting 23 ish mpg. i dont believe it can be injectors as it would miss all the time. possibly slighty clogged cat? my next step will be compression check. just wanted to possibly get alittle more advice, maybe im missing something. thx for any info. also car is basically stock

did you gap your plugs when you put them in or jjust straight out of the box? sometimes the tip of a plug may be bent out of the box.

[QUOTE=BLKWS6;16412903]did you gap your plugs when you put them in or jjust straight out of the box? sometimes the tip of a plug may be bent out of the box.[/QUOTE

I gaped them all at 50. Misfire was there before and after plug change

50 is a bit large on these cars but it shouldnt cause a misfire. most run .35-.40 (thousandsths) gap on them.

if its not throwing any codes i wouldnt be too concerned with it but keep an eye out for anything else that may change.

[QUOTE=BLKWS6;16412980]50 is a bit large on these cars but it shouldnt cause a misfire. most run .35-.40 (thousandsths) gap on them.

if its not throwing any codes i wouldnt be too concerned with it but keep an eye out for anything else that may change.[/QUOTE


Ok thx for the info. Its just extremely annoying not being able to figure it out. you can watch it on the scanner and each cyl will start to misfire randomly so i know something is not right. I'm just trying to get it 100% so i can do some mods an tune an it run to its full potential.

I had a similar problem. Is your TCS off light lit up when you drive?

I had a similar problem. Is your TCS off light lit up when you drive?
Tcs light is not lit up. Unless I hit the switch. But what would that cause if it was?

to me it sounds like a ignition control module. they some times act up when warm. do you know what cylinders are missing? do you have a scanner to count the knock on each cylinder????

to me it sounds like a ignition control module. they some times act up when warm. do you know what cylinders are missing? do you have a scanner to count the knock on each cylinder????

It seems to just be random. And yes I have access to a scanner not just a code reader. I will check again tomorrow and give exact number( misfire per cyl ). Is there anyway to check icm without buying one. Or would that just be easier?.

My situtation the light was on and it was surging when accelerating and idled rough. I guess it goes in to a speed density tune when the throttle postion sensor goes bad. I never had a check engine light come on. So I took a $40 risk and replaced it and as soon as I started it I knew it fixed it. Has ran great since. But I think the tps sensor gives input to determine the tcs sensor so I'm not sure in your case if thats it.

do you know if its one cylinder or more, all of them are missing. it would tell me alot on what happening.

I didn't investigate that far.

do you know if its one cylinder or more, all of them are missing. it would tell me alot on what happening.

Its not just one cyl. It seems to just bounce around. When idle I see anywhere from 1-4 mis fire .if i remember correctly. It will jump around from say cyl1 to cyl 4 just a random cycle.

whats the fuel presure? and with it jumping just between those two cylinders. it has to share a common issue. the icm is out of the picture. i wouldnt think it is compression. im leaning toward fuel to me. befor i would spend any more money i would swap out the injectors from cylinder to cylinder and see if it follows. the windings in the injectors might be screwing up when warm. and does the misfire happens right when it hits operating temp? or when it gets warm?

whats the fuel presure? and with it jumping just between those two cylinders. it has to share a common issue. the icm is out of the picture. i wouldnt think it is compression. im leaning toward fuel to me. befor i would spend any more money i would swap out the injectors from cylinder to cylinder and see if it follows. the windings in the injectors might be screwing up when warm. and does the misfire happens right when it hits operating temp? or when it gets warm?

Fuel pressure is unknown. I have not checked it. An seems to start missing once it hits 175 or so. Does not have to be at operating temp to experience misfire.

I know you changed the 02 sensors.....new ones are often bad. Scan it and see how they are switching with the engine idling and HOT.

And no....you will not get codes or SES light until they almost totally fail.

Clean the MAF too.......if dirty they will cause problems at all rpm's.....

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