Somebody put popcorn kernels in my new Cat... - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-31-2003, 06:46 PM   #1
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Default Somebody put popcorn kernels in my new Cat...

Here'* the story....

(For reference my car'* a '96 Bonnie SSEi)

My Catalytic Converter had been on the fritz for a while, gradually getting louder and louder, and I just got it fixed three days ago. My car is running quieter than it did when I got it 2 years ago, and for an hour or two it even seemed a good deal faster 0-40MPH, but that night it started backfiring a little bit under heavy load, and since then its been backfiring like crazy under load (3K RPMs or higher in most gears). It loses a little power when it backfires but it doesn't really surge much, and it doesn't backfire as much at higher speeds. It also sporadically stops BF'ing at 70MPH with WOT.

I tried resetting the PCM today (disconnected both batt. terminals for 1/2 hour), and it didn't make a difference in the backfire, but i'm not sure if it even reset the computer 'cause it'* still running the same as before to a tee. I'm about to put in the new PCV that i've had sitting around for a month at least, but I doubt that'll do much.

My questions for you guys:

1. How do you properly reset the ECU? I saw something in a post somewhere in my extensive searching that said something about pulling two fuses, but i'm not even sure now if that was for an L67.

2. Any ideas on why it might be backfiring? The cat was split down the side and a good deal of the exhaust was coming out right there, so could the 02 sensor have been sending screwy signals? It smelled like it was running really rich all the time, and my mileage seemed to worsen when the cat was screwed up, but I could be mistaken.

3. How many 02 sensors does the L67 have? I can see the one on the exhaust manifold right before the DP, but is there another after the cat?

Any help/advice/etc... is greatly appreciated.
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Old 12-31-2003, 07:04 PM   #2
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Disconnect the neg terminal at the battery for 1 hour. This should clear the PCM.

Backfires are usually due to lean conditions, the 02 sensor could be sending wierd data causing this. Do you have an autotap or simlar device to check?

the L67 sould have 2 o2 sensors. One in the rear maniforld the other next to the cat.
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Old 12-31-2003, 08:13 PM   #3
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An hour? Wow was I off...

I'm assuming that an Autotap is some kinda OBD2 scanner? I don't have one, but would Autozone let me use theirs to check stuff out while I run the car? I've heard they pull codes for you for free.

I'm gonna end up goin back to the shop that installed the cat 'cause they'll check it out for free, but anything else I should try in the meantime?

Lastly, would I have any problems doin' some highway driving tonight assuming that I drive nice an' easy?
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Old 12-31-2003, 08:23 PM   #4
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Evilsaint, put your location in your profile. We may have someone near you with a scantool.
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Old 12-31-2003, 09:01 PM   #5
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Done and Done...
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Old 01-03-2004, 04:43 PM   #6
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Turns out I was wrong. My car wasn't backfiring; The noise is supposedely some chain inside the tranny slipping. Thanks for you help anyways guys, and thank god for extended warranties.
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