243,720 mile misfire! Help!

[R1up0n1]

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.

That EGR valve is expensive to replace, and I think it's been bad for the past 100k miles, but it's never really effected the car....That EGR valve really doesn't do too much but recycle the exhuast gas back into the engine. I don't think this would cause the car to mis and backfire.

Does anyone know of any ALDL software that will work on my laptop for a 1994 Firebird with a 3.4 V6. 12 pin OBD 1?
I can find tons of software for the LT1, but not the 3.4.

[StrtRacer98]

Re: 243,720 mile misfire! Help!

I also had a similar problem and it was a clogged cat, might wanna try it to just rule it out, pull the o2 sensor out, in front of the cat and if it runs better, it could be clogged.
anyway, good luck.. and wow, to the 240k+ miles way to go!, hows the exterior look?

[bah]

Re: 243,720 mile misfire! Help!

That EGR valve is expensive to replace, and I think it's been bad for the past 100k miles, but it's never really effected the car....That EGR valve really doesn't do too much but recycle the exhuast gas back into the engine. I don't think this would cause the car to mis and backfire.

Does anyone know of any ALDL software that will work on my laptop for a 1994 Firebird with a 3.4 V6. 12 pin OBD 1?
I can find tons of software for the LT1, but not the 3.4.

but i believe the sensors in the egr tell the computer how much fuel to deliver according to how much exhaust gas is being put back in, so you could be running lean simply because it doesnt have that exhaust gas, somebody can correct me if i am wrong, but i'm pretty sure thats how it works, and you might want to check it out, and it wouldnt hurt to do egr delete, this is all you have to do and it wont throw codes


just block off the port on the header and put a breather on the egr tube and it only sucks fresh air

[PalmHarborBlkv6]

Re: 243,720 mile misfire! Help!

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.

It sounds to me like you have spent a lot of money replacing parts like crazy...spent money going to an independent garage and you are in the same place you were at the start.
My God, don't be so stubborn, bring it to a Chevrolet Dealer and they won't charge you if they cannot fix it (which I doubt)...they also warranty parts for life. They know this motor better than anyone and I bet they will diagnosis it and fix it in less than 90 minutes. You have spent money & time so far for nothing. Use your head and bring it those who make the damn car.

[MrCoffee]

Re: 243,720 mile misfire! Help!

or because you're probably really close to finding out what the problem is, continue to diagnose and replace. The truth is, what you've done so far would need to be done eventually anyway. So while you've spent the money and it didnt fix the problem, at least you've quite possibly avoided another.

I have no idea what your problem is so I cant offer any help, sorry. But definitly congrats on the milage. Good luck with the rest of your diagnostic.

[MikeA]

Re: 243,720 mile misfire! Help!

When my EGR went bad, my car ran as bad as you can imagine. Change it, or do a delete like someone else suggested.

[R1up0n1]

Re: 243,720 mile misfire! Help!

I also had a similar problem and it was a clogged cat, might wanna try it to just rule it out, pull the o2 sensor out, in front of the cat and if it runs better, it could be clogged.
anyway, good luck.. and wow, to the 240k+ miles way to go!, hows the exterior look?

It's a new cat, so I don't think it's that at all, I'm not quite sure the new cat even has an o2 sensor on it.
Oh and the exterior is in pretty good shape, some minor blemishes, but after a wax she still looks like a red cherry!....the interior is almost flawless.

but i believe the sensors in the egr tell the computer how much fuel to deliver according to how much exhaust gas is being put back in, so you could be running lean simply because it doesnt have that exhaust gas, somebody can correct me if i am wrong, but i'm pretty sure thats how it works, and you might want to check it out, and it wouldnt hurt to do egr delete, this is all you have to do and it wont throw codes


just block off the port on the header and put a breather on the egr tube and it only sucks fresh air

I am going to bypass the EGR this afternoon or tomorrow to see if this works.

It sounds to me like you have spent a lot of money replacing parts like crazy...spent money going to an independent garage and you are in the same place you were at the start.
My God, don't be so stubborn, bring it to a Chevrolet Dealer and they won't charge you if they cannot fix it (which I doubt)...they also warranty parts for life. They know this motor better than anyone and I bet they will diagnosis it and fix it in less than 90 minutes. You have spent money & time so far for nothing. Use your head and bring it those who make the damn car.

I will take it to a garage if I don't find out what it is soon...I just feel like I'm so close to figureing it out.

or because you're probably really close to finding out what the problem is, continue to diagnose and replace. The truth is, what you've done so far would need to be done eventually anyway. So while you've spent the money and it didnt fix the problem, at least you've quite possibly avoided another.

I have no idea what your problem is so I cant offer any help, sorry. But definitly congrats on the milage. Good luck with the rest of your diagnostic.

Yeah everything I've done so far is stuff that was due to be done anyway.

When my EGR went bad, my car ran as bad as you can imagine. Change it, or do a delete like someone else suggested.

I'm going to bypass or delete it today or tomorrow.

[R1up0n1]

Re: 243,720 mile misfire! Help!

I bought the breather filter to "delete" the EGR valve a few minutes ago, but I gotta make a block off plate for the intake manifold.

[R1up0n1]

Re: 243,720 mile misfire! Help!

I did the install tonight to delete the EGR Valve. I made a metal custom fit block off plate to block the hole on the intake manifold, sealed it up with RTV sealant, then screwed it down.
Next I installed the breather filter on the end of the hose, and I decided to go ahead and replace the EGR valve gasket and seal it up with RTV sealant just to be sure there are no leaks.
I then disconnected the battery for 5 minutes to be sure to clear all codes.

I started up the car... still have the high idle, and still got the mis-fire, and backfire.
So essentually I don't think the EGR valve is the problem.

[Skyhawk101]

Re: 243,720 mile misfire! Help!

Still think it maybe a coil pack or cam shaft sensor. Need to get another good code read since you replaced the TPS and Oxygen sensors. I agree, it's probably not the EGR since you by-passed it. What would cause the idle to run high? Solve that and you'll probably solve the miss/backfire.

[R1up0n1]

Re: 243,720 mile misfire! Help!

Ok I'm still stumped on this!

Here is a list of everything I've replaced in no particular order and it's still not running right.

1. All 3 coil packs
2. (ICM) Ignition Control Module
3. All 6 spark plugs
4. All 6 ignition wires
5. (IAC) Idle Air Control Valve
6. O2 sensors
7. (TPS) Throttle Position Sensor
8.. Fuel Filter
- Fuel pump tested fine
- All Vacuum lines tested fine
- Camshaft Position Sensor tested out fine.

Compression Test:
-Cylinder 2 = 150 PSI
-Cylinder 4 = 152 PSI
-Cylinder 6 = 150 PSI

I bypassed the EGR Valve

Nothing in the misfire/backfire is setting off the SES light either.

Anymore ideas of what could be wrong????

[slow6]

Re: 243,720 mile misfire! Help!

just a guess but maybe its running rich due to the !EGR?
have you unplugged your battery for 30 minutes after you !EGRed?

[R1up0n1]

Re: 243,720 mile misfire! Help!

just a guess but maybe its running rich due to the !EGR?
have you unplugged your battery for 30 minutes after you !EGRed?

Yeah I unplugged the battery for about 20 minutes while I checked some other things out. I'm not too concerned with the running rich part...but I am concerned about what would make the engine mis and backfire tho.

[slow6]

Re: 243,720 mile misfire! Help!

sorry, didnt realize it was backfiring
reasons for backfiring:
1) bad egr
2) incorrect ignition timing (wtf?)
3) vacuum leak
4) bad valve springs or stuck valves
5) intake air (vacuum) leak

[slow6]

Re: 243,720 mile misfire! Help!

oh yah, 150-155 psi compression kinda seems low to me, but it might just be
because your engine has a decent amount of miles.
My engine (before it died on me) was showing compression of 180 psi, which still might be a little low (32k miles).