The car is a 1997 Bonneville SE with the N/A engine. It'* got 145K on the odometer and there are a few problems. I recently (a week ago) drove a 800 mile, 13 hour trip from Memphis to Fort Bragg, NC with the car. Here are the problems I found.

The first, and most noticeable problem is the slipping transmission. When you take off from zero, the car accelerates fine, shifts to second gear and then slips almost immediately. You can put your foot into it, but it will accelerate very slowly until about 35MPH when the tranny shifts into 3rd. After that, everything is perfect. The TCC engages correctly and smoothly. Is this just a "tranny rebuild" type of problem?

Now, while driving 80MPH almost the entire time during the trip, I found that the car misfires a lot when under load. This happened the most when driving through the mountains in eastern TN and western NC. Although, even on the flattest land, the tach bounces about 75RPMs or so when cruising down the highway. If you need to accelerate, even from 55 or so, the car bucks and backfires the whole way to 80. Is this just a plug-and-wire kind of problem.

The car starts quicker than my 1998 Eighty-Eight with 80K miles on it. It idles nice and smooth, too. The fuel pump has been replaced about 8K miles ago. No check engine lights, even when misfiring on the highway.

Any suggestions?

Nick

Sounds like a 1-2 shift valve stuck or binding. Can you manually shift in to second?

As for the stuttering, I would change the plugs and perhaps the plug wires.

I'll try manually selecting 2nd. It seems that a sticky shift valve would be the ideal problem.

Thanks,
Nick

That will involve removing the transmission, or at the very least, lowering it down enough to remove the side pan. Then the solenoids will be right there. I suggest spending the extra $60 and replacing the EPC solenoid while your there.

OK. The slipping problem goes away after manually selecting 2nd gear.

Would there be any chance in freeing a sticking solenoid by changing the fluid after using a detergent to break anything up, or is this most likely a mechanical failure with the solenoid?

Thanks,
Nick

There is the slight chance that will free up a sticking valve. But if it'* the solenoid, then nothing will change.

Thanks. After another 12 hour trip, I noticed that I was quite wrong. The slipping happens in 3rd gear, not 2nd. In Drive, it will accelerate from a stop, shift to 2nd, and then drop out at 3rd, the tranny seems like its in neutral. If I am able to accelerate to 40MPH, 4th drive will kick in.

He'* got a 1997 SE, not supercharged. That was the last Bonneville to use the 4T60-E transmission, so that takes EPC issues off the table.

The surging 75 RPM may be the TCC/valve body issue, though that wouldn't explain the other problems.

Just seeing the post. It'* likely that your third gear clutches are worn out. It'* one of the common things on higher mileage transmissions.