243,720 mile misfire! Help!

[R1up0n1]

I think i have read thru all the misfire threads, however mine is a little different...

I have a 1994 Firebird 3.4 V6 which I have owned since day 1. All of my maitanence has always been done on time. The shocker is I now have 243,720 miles and the car still runs awesome until now...

Last week I started to get a misfire, rough acceleration and a back fire in the engine bay at or about 2200 - 3500 RPM.

Everything I seem to try is not solving the problem. I replaced the plugs, wires, and fuel filter. Problem still exist.
I took the car to the shop to have a diagnostic done....they came up with Throttle Positioning Sensor, Oxygen Sensors, and EGR valve. I then replaced the Throttle Positioning Sensor, and Oxygen sensors. Yet my problem still there!
My Service Engine Soon light has always been a little goofy...on and off while driving so I don't really trust that. However it's not really coming on too much since I replaced those Oxygen Sensors.

The checked the primary and secondary Ohms on all the coil packs and those came up perfectly fine. I am getting spark to each plug. I also had a fuel pressure test done, and that came up fine. I took the throttle body apart tonight and cleaned that all up, along with the EGR valve...that still didn't fix the problem.
Oh I also have a new exhaust, and cat. converter about a month old.
I took the car to get scanned at advance auto earlier and they couldn't even get the code scanner to work on my car....which I've ran into that before.

If anyone can give me some more leads I'd appreciate it...I'm just trying to save my baby with 243,720 miles on her...oh by the way the engine is not knocking, or anything like that....just a misses, and backfires during acceleration after warm up at or about 2200-3200 rpm.

[Everglades W68]

Re: 243,720 mile misfire! Help!

It sure sounds like bad coil(s) or wire(s).

[R1up0n1]

Re: 243,720 mile misfire! Help!

It sure sounds like bad coil(s) or wire(s).

But I just replaced the plugs and wires with AC Delco's, and I also tested the coil packs both ways....everything came up perfectly fine....

I was reading the repair manual and I noticed the camshaft sensor could cause a stumble or misfire...but I can't even locate the thing on my engine!

[Fred]

Re: 243,720 mile misfire! Help!

Congratulations on so many miles!

[R1up0n1]

Re: 243,720 mile misfire! Help!

Congratulations on so many miles!

Thanks! I take care of it.

Any other idea's or clues how to fix the problem? I'm beating my head against the wall on this one....

[R1up0n1]

Re: 243,720 mile misfire! Help!

Bump! :D

[loser]

Re: 243,720 mile misfire! Help!

fuel filter? and im pretty sure your right about the crank positon sensor, or the cam posistion sensor. my dads car had a similar problem and it ended up being the fuel filter, but his car wasnt throwing an SES light. did you try running a bottle of sea-foam threw it? with those miles ( impressive BTW ) will probally help a bit. does it idle fine? my dads car done fine up to about 30MPH and light throttle, anything more and it would stumble bad, almost stalling.

[BLLDOGG]

Re: 243,720 mile misfire! Help!

I need a list of the codes please :)

could be clogged injectors, could still be coils because you are having problems under load, I doubt they are testing the coil packs at 2500rpms. it could be several things and your codes would help us figure it out. I promise, your ses light is acurate, you just might have been having intermediate issues you were not awair of. congrades on the mileage and the reason autozone couldnt read your codes is because you have OBD 1 . they probably no longer have the scanner for that since it is about 11 years old.

[R1up0n1]

Re: 243,720 mile misfire! Help!

fuel filter? and im pretty sure your right about the crank positon sensor, or the cam posistion sensor. my dads car had a similar problem and it ended up being the fuel filter, but his car wasnt throwing an SES light. did you try running a bottle of sea-foam threw it? with those miles ( impressive BTW ) will probally help a bit. does it idle fine? my dads car done fine up to about 30MPH and light throttle, anything more and it would stumble bad, almost stalling.

I just replaced the fuel filter last week and that didn't fix the problem. I want to replace the cam shaft position sensor but I can't find the damn thing....I read the manual and it says above the timing chain cover and in front of the intake manifold...yet I don't see it.
I ran a bottle of fuel injector cleaner thru it...that didn't help either.
Once the car gets up to normal operating temp and under load about 2200-3500 rpm it stumbles, and backfires. I HAVE noticed the idle is up really high about 1500 at all times until I put it in Drive, or turn on the A/C.

The SES light isn't really coming on since I replaced those 0-2 sensors.

[Jayjay269]

Re: 243,720 mile misfire! Help!

I had the SAME exact problem with mine. It kept throwing a misfire code so I changed the plugs and wires, that fixed it for a while, then it did it again on the SAME cylinders, so i changed the coil pack, plugs and wires on the same two cylinders that has fixed the problem. Thing is, if you change one coil pack, you might as well change the other two including all the plugs and wires. It would be best if you do it yourself, its going to save you a TON of money. It doesn't take that long to change them, but it will take a min. or two to change the plugs and wires!!! Good luck!!

Jay

[R1up0n1]

Re: 243,720 mile misfire! Help!

I need a list of the codes please :)

could be clogged injectors, could still be coils because you are having problems under load, I doubt they are testing the coil packs at 2500rpms. it could be several things and your codes would help us figure it out. I promise, your ses light is acurate, you just might have been having intermediate issues you were not awair of. congrades on the mileage and the reason autozone couldnt read your codes is because you have OBD 1 . they probably no longer have the scanner for that since it is about 11 years old.

I didn't get a list of the codes....the mechanic just told me it was reading 0-2 sensor, TPS sensor, and EGR. I replaced 2 of the 3 problems and it didn't fix the problem.
It could be a clogged injector, however I'm not so sure an injector would cause a backfire which is an explosion inside the cylinder. When the stumble and backfire happens it is NOT setting off my SES light.
The advance auto I went to had the OBD 1 scanner, but it would not work with my car for some reason.

[R1up0n1]

Re: 243,720 mile misfire! Help!

I had the SAME exact problem with mine. It kept throwing a misfire code so I changed the plugs and wires, that fixed it for a while, then it did it again on the SAME cylinders, so i changed the coil pack, plugs and wires on the same two cylinders that has fixed the problem. Thing is, if you change one coil pack, you might as well change the other two including all the plugs and wires. It would be best if you do it yourself, its going to save you a TON of money. It doesn't take that long to change them, but it will take a min. or two to change the plugs and wires!!! Good luck!!

Jay

The first thing I did was the plugs and wires...still didn't fix the problem. I'm not even getting an SES light when I get the backfire and stumble. I'd just hate to replace all 3 coil packs and it's not the problem because I tested them by the primary and secondary test and they appear to be ok. I do all the work myself if I can tho. The hell with paying someone if I can do the work.

[Jayjay269]

Re: 243,720 mile misfire! Help!

When was the last time you changed your cat??? I also went through the same thing with my old stock cat that was clogged. It would accelerate up to about 3000 RPM's and then it would just go to crap and I would get NOTHING as far as power from the engine. I took it to a friend who is a mechanic, of course he has a comp. to run codes. All it was showing was a misfire on #1 and #3 cylinders, then we went through a LOOOOOOONG list of things that it could be, so I took a shot at one of them, low and behold, I got it right the first time. It was my cat. so I went ahead and changed it out with a magna flow cat, runs like a charm. I was even stunned at how smooth the engine accelerated and how fast she was begging to go!! Good luck with fixing your ride

Jay

[R1up0n1]

Re: 243,720 mile misfire! Help!

When was the last time you changed your cat??? I also went through the same thing with my old stock cat that was clogged. It would accelerate up to about 3000 RPM's and then it would just go to crap and I would get NOTHING as far as power from the engine. I took it to a friend who is a mechanic, of course he has a comp. to run codes. All it was showing was a misfire on #1 and #3 cylinders, then we went through a LOOOOOOONG list of things that it could be, so I took a shot at one of them, low and behold, I got it right the first time. It was my cat. so I went ahead and changed it out with a magna flow cat, runs like a charm. I was even stunned at how smooth the engine accelerated and how fast she was begging to go!! Good luck with fixing your ride

Jay

I just put a new CAT on about 20k miles ago, and a new muffler about 1,000 miles ago.

[MikeA]

Re: 243,720 mile misfire! Help!

If you got three trouble codes and only fixed two of the three and the problem didn't get better, why not fix the third and see what happens? If you never replaced your EGR valve and you have that many miles it could be shot. Mine went dead at 80K. Good Luck.