Thread: Mind-Boggling Scenario. 3.29 Gear Ratio Programmed to PCM. 3.03's In transmission.

So, Story. My transmission dropped out of my 1999 Grand Prix SE. Just so Happened I had a 30K Mile transmission at work that I could have at no cost. So I swapped it in. It was out of a 98 Buick Park Avenue.

As I see it. It has 3.03 Gears in it. Where as my Factory transmission has 3.29's. All is fine and dandy. Except one issue, The PCM Sees the transmission as its slipping due to the different gear ratio. Altho its not truly slipping. It is Pushing full line pressure to the solenoids. Almost as if it has a strong shift kit installed.

I can, And Have dealt with it for a while but. Out of curiosity. I attempted to use the PCM out of the Buick to see if it would work. Surprisingly my car started with the Buick PCM. Altho they were visually different the Connectors were the same. But the bad. My Grand prix was missing/Running on 2-3 Cylinders. And my fuel gauge read empty.

Is there anything I can do to use the Buick PCM. Or Anything I can do to my factory PCM to make it shift like it should? Kinda gets old slamming into gears. And being able to break traction going 60 on a wet road punching the gas.

I'm guessing the buick had the 3800 and your se has the 3100? They have different firing orders. You need to get your pcm tuned for the gear ratio change.

Both cars are 3.8

You must reprogram your grand prix PCM, there is no other way around it.

As in with a tuner.

Originally Posted by Fivefingerdeathpunch

You must reprogram your grand prix PCM, there is no other way around it.

As in with a tuner.

You or anyone else know of anyone in my general area that could do it without me sending my PCM off? I have a guy with a Tech 2 But he couldnt do anything.