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1992 GM 3800 backfiring, running rough

I have a 92 Pontiac Bonneville SE with the 3800 FI motor. It has always idled kind of rough, and is now having other problems. When putting the motor under load at low RPM, like going up a hill on the highway, it feels like the transmission starts to shudder. But I think it's something in the motor, not the transmission.

When accelerating hard I can feel 'hicups', or brief lapses in power throughout the RPM range. While holding the brake in the driveway and running the car up to ~3000 RPM in drive, I can see the tach dip as these hicups occur. If the problem was the transmission slipping, I would think the tach would bump up when these occur.

And then lately I've heard a pop from under the hood while accelerating, which I assume is a back fire. I have a brief loss of power when it happens.

20,000 miles ago I put on new plugs, wires and an O2 sensor.

Any ideas where I should start looking for the problem?

Thanks for any help.

-Ryan

Reply to
Ryan
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Sounds like you might have switched a spark plug wire and have them reversed on two plugs. I'd check the firing order and make sure they're right. It's possible that the timing is off and needs to be adjusted as well. You should get a timing light and get that checked. If you can't, turn the distributor a couple degrees one way and see if the problem abates, if not, turn back the other way and check again. Good luck,

-Bruce

Reply to
Bruce Chang

What distributor?

Reply to
Neil Nelson

Thanks for the reply. There is no distributor on this car, all electronic. I don't know if the timing can even be adjusted on these. Will check the wires, but unless some oil change shop switched them they are ok because I haven't touched them for 20K miles...

-Ryan

Reply to
Ryan

I about pulled my hair out trying to fix this one on an Olds once. Dollars to donuts your problem is the ignition module underneath the coil pack. Is there goo coming out of it by any chance and dripping on to the stuff underneath it?

Unfortunatley this isn't a cheap part (probably over $100). You might try to find one in the yard.... just make sure the "juices" aren't leaking out of it.

Steve B.

Reply to
Joe

Yeah, since there is no distributor, you won't be able to adjust the timing. I dind't realize it was a DIS car. You said you changed the wires and plugs and that's why I thought you might have gotten a wire switched.

Reply to
Bruce Chang

Joe's answer sounds quite good. But, if it has a mass air flow sensor, tap on it with a small, closed pocket knife. If that sets the shuttering in motion & esp. if it stops it when tapped again, replace it. Shouldn't cost too much. Plus it's easy to change. Let's hope it's not that module under the coil pack that Joe told you about, altho' it can have the same symptoms. HTH & good luck, sdlomi

Reply to
sdlomi

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