Extremely random misfire

[SoulReaver]

Every once and a while, and I certainly do mean WHILE, my car will run like total dog crap for maybe like 3 minutes tops. I can drive it fine for 3 weeks, then for 3 minutes it will randomly just suck. The car will smell like gas terribly, and sputter and pop. If I gas it enough, it will kick out of it and I'll be alright. Anyone know what it could be?

I know, I know, check the opti... Anything else though? Maybe the fuel pump is shitting out? any thoughts?

[SoulReaver]

Oh yeah, it has brand spanking new plugs and wires. Like not even a month old.

[SnyperBob]

What about a fuel filter. What kind of gas are you runnin?

[SoulReaver]

Only premium. I'm tuned exclusively for that type of gas. The filter is new, just changed it like 5k miles ago with my brakes. I thought it could be that too though. I may change it soon, thy are only like 15 bucks.

[SnyperBob]

hmmm, did the problem start after the last filter change. Maybe it's a bad one or clogged for some reason.

Do you think it's related to humidity or something like that?

[SoulReaver]

I dunno. It's so fuckin random it pisses me off. The problem may have started before I had my wires and plugs done. I couldn't really tell since I was driving the car while it was running like ass. So as far as I knew, it was just the plugs and wires. I drove the car for a week after having the stuff done, then all of a sudden it ran like piss. And has run weird ever since.

Like I said, I can drive for a month and it will be fine, then run like ass for a whole 3 minutes, then run great again. Weird.

[Adam]

Does it throw a check engine in that 3 minutes?

[SoulReaver]

Yes

[Adam]

well did you get it scanned?

[SoulReaver]

Yeah it comes up as random cylinder misfire, and recently I had a low voltage to my 02 sensors. Maybe it's the 02's?

[SnyperBob]

I dunno. I say you should just drive it like you stole it. I don't think you have any problem doing that :)

[Fixxer99TA]

Yes, O2 sensors... Get em' replaced :D

(If it runs like crap for 3 minutes, then goes back to normal for hours on end... Then its those pesky O2s sending fouled signals).

[SoulReaver]

Yes, O2 sensors... Get em' replaced :D

(If it runs like crap for 3 minutes, then goes back to normal for hours on end... Then its those pesky O2s sending fouled signals).

They should be in warranty still, so I'll go get em fixed! wewt.

[Fixxer99TA]

Everyone loves Free :D

[hempkat94z]

I am having the same problem that started just a few weeks ago. Now I have a severe rich problem which is also probably the O2s but i have no codes. When I installed the LT headers i had to splice my O2 wires to extend for the new O2 location. Not to hyjack yur thread but does anyone know of a O2 plug extensions.

[Alex94TAGT]

I am having the same problem that started just a few weeks ago. Now I have a severe rich problem which is also probably the O2s but i have no codes. When I installed the LT headers i had to splice my O2 wires to extend for the new O2 location. Not to hyjack yur thread but does anyone know of a O2 plug extensions.

Few thoughts:

1) I was always under the impression that the factory wires routing to your oxygen sensors have a waxy coating, and trying to extend them yourself can cause slight variances in the electrical signals. Given that the sensors rapidly fluctuate from 100mV to 900mV (.1 to .9v), a small variance can really screw up fueling. If you have to extend them, extend them on the sensors themselves as opposed to the factory harness, but you really should use the O2 extensions intended for this purpose. ThunderRacing sells the extensions, for one. 1994's use the flat 4-pin connector.

I would also check for any exhaust leaks, because that will allow excess oxygen into the exhaust, which will get picked up by the sensors, which will tell the PCM you're running lean. The PCM responds by adding more fuel, which you don't need. The result is a rich running condition.

Incidentally, a misfire will also cause this. Without combustion, excess oxygen from the cylinder is going into the exhaust. Oxygen sensors only detect oxygen, not fuel, so this will get picked up as a lean condition as well.

-------------------
2) If you have a 1994 or 1995 Lt1, I'd strongly recommend the Scanmaster LT1. Not only can you read DTC's, but it will also show you block learns/long term fuel trim for either bank. By looking at those numbers, you can easily determine which bank is misfiring. The computer will be adding fuel (block learns will rise above 128 counts up to 160 max, which means the PCM is adding fuel).

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3) Small tip I learned this summer: After having a slight misfire at idle for a while, and knowing that it was on the passenger bank by looking at the Scanmaster, I decided to start the car and use an infrared temperature gauge on the header primary tubes. I found that cylinder #2 was about 50-degrees behind the others. Pulled the wire and found a pinhole in the spark plug boot. Replaced the boot with a spare MSD, and it runs great. Had the misfire for a month, and it took five minutes to fix.

But yeah, if you're having a random misfire, it's likely between the PCM/wiring, coil/ICM, and Optispark (as ALL cylinders are apparently being affected). Otherwise, the 1996-1997 OBD2 vehicles should theoretically be able to tell you what individual cylinder(s) are misfiring, thanks to that pesky crank sensor.

[phantomzer0]

Few thoughts:

1) I was always under the impression that the factory wires routing to your oxygen sensors have a waxy coating, and trying to extend them yourself can cause slight variances in the electrical signals. Given that the sensors rapidly fluctuate from 100mV to 900mV (.1 to .9v), a small variance can really screw up fueling. If you have to extend them, extend them on the sensors themselves as opposed to the factory harness, but you really should use the O2 extensions intended for this purpose. ThunderRacing sells the extensions, for one. 1994's use the flat 4-pin connector.

The wiring is very specific. We had them wired originally on the camaro and after taking it to an f-body only mechanic. he confirmed that the wiring needs to be precise because of the fluctuation in voltages.

[my95z28]

I don't think that your problem is o2 sensors. You can run a vehicle with no o2 sensors in it.It will revert back to a basic fuel map that I believe is adjusted by your throttle position. It will get terrible gas mileage, but will not missfire.

[Twisted Z]

Actually the deal is the O2s recieve Oxygen referance through the wire area of the sensor.

ANY THING you do to the wiring is going to change the voltage guys be fair ;)

YES you can run with out them BUT if they are lieing to the PCM it Will follow there lead ;) If it tell the PCM to pour fuel to it or take a bunch away Mis-fires WILL result.

[hempkat94z]

Few thoughts:

1) I was always under the impression that the factory wires routing to your oxygen sensors have a waxy coating, and trying to extend them yourself can cause slight variances in the electrical signals. Given that the sensors rapidly fluctuate from 100mV to 900mV (.1 to .9v), a small variance can really screw up fueling. If you have to extend them, extend them on the sensors themselves as opposed to the factory harness, but you really should use the O2 extensions intended for this purpose. ThunderRacing sells the extensions, for one. 1994's use the flat 4-pin connector.

I would also check for any exhaust leaks, because that will allow excess oxygen into the exhaust, which will get picked up by the sensors, which will tell the PCM you're running lean. The PCM responds by adding more fuel, which you don't need. The result is a rich running condition.

Incidentally, a misfire will also cause this. Without combustion, excess oxygen from the cylinder is going into the exhaust. Oxygen sensors only detect oxygen, not fuel, so this will get picked up as a lean condition as well.

-------------------
2) If you have a 1994 or 1995 Lt1, I'd strongly recommend the Scanmaster LT1. Not only can you read DTC's, but it will also show you block learns/long term fuel trim for either bank. By looking at those numbers, you can easily determine which bank is misfiring. The computer will be adding fuel (block learns will rise above 128 counts up to 160 max, which means the PCM is adding fuel).

-------------------
3) Small tip I learned this summer: After having a slight misfire at idle for a while, and knowing that it was on the passenger bank by looking at the Scanmaster, I decided to start the car and use an infrared temperature gauge on the header primary tubes. I found that cylinder #2 was about 50-degrees behind the others. Pulled the wire and found a pinhole in the spark plug boot. Replaced the boot with a spare MSD, and it runs great. Had the misfire for a month, and it took five minutes to fix.

But yeah, if you're having a random misfire, it's likely between the PCM/wiring, coil/ICM, and Optispark (as ALL cylinders are apparently being affected). Otherwise, the 1996-1997 OBD2 vehicles should theoretically be able to tell you what individual cylinder(s) are misfiring, thanks to that pesky crank sensor.

I have put it on the scanner right after I had spliced the wires. Which was when I learned that you should not splice then....LOL. They were cycling fine at first but that was right after I had spliced them. That was also when i had learned that they made extensions but no one around here knew for sure where to get them. Thank you for letting me know that Thunder Racing has them. These are still the original O2s which have 150,000 miles on them but the engine was rebuilt at 78,000 miles by a local dealership when it lost oil pressure. I have brand new plugs and wires. (TR55s with JEGS 8.5mms and new coil) hoping that was maybe the problem which the misfire that I think I had is gone. Put it on the scanner today and it looks like I need to replace the wire harnes for the O2s with extensions and new O2s. I didn't find no exhaust leaks as of yet...LOL Thanks guys for the help! I need all I can get!

[MAKI]

Its good possibility that its your o2s. I ruined a pair because of some outrageous backfiring.

Also check your coil.

[Fixxer99TA]

Any updates SR? Fix it yet?