not shifting when supposed to

I have a 1997 grand prix 3.8 with 180,000 miles on it. I have had it for 6 years now and I just swapped the motor with a used engine with 65,000 miles on that one everything went well until I took it on a test drive and now the car will not shift until it reaches 4.5 rpm it is way over revving. I had the filter and everything changed in 04 when I got it. Could the filter be clogged up? I am at a loss right now it runs but it is not shifting when it is supposed to unless I gun it and then it shifts just fine. Any IDEAS?????? :banghead:

Hi, Welcome to AF!

What year of car did your donor motor come from? And the million dollar question, when you swapped the motor over, did you swap the PCM's?

I am betting if you swapped the PCM's that you have a PCM from a car that had a trans with a different final drive gear ratio than yours. If this is the case, you could either swap in the old PCM, depending on the wiring harness differences, you may need to swap pins around. Or you could find someone you know with a tuner and have them tune the new pcm with your trans final gear ratio.

1997 grand prix and i didnt change over the pcm's

anyone have any other ideas please help

do you know if the replacement trans was a 4t65e or a 4t60e?

i havent replaced the trans just the engine. i had trans flushed and filter when i got the car to be on the safe side cause it had 80,000 on it and no record of it being done.

What model GP is this? SE, GT or GTP?

Since this is a 1997 model GP the OP (JeremyBirkhimer) could have the M13 4T60E autotransaxle with the vacuum modulator which controls line pressure for shifting. So if not a GTP with 4T65E-HD tranny check the vacuum line to the modulator on the transaxle. If above checks good the vacuum modulator could be bad or the engine vacuum is not correct.

is the se model, the vacuum is good and the pipe is clear air is moving through, would the modulator be bad then...im so confused thanks everybody for the help

i will get part tomm and let you all know how it goes also gonna get it scanned at autozone while im out see what they can tell me.

The scanners at like Autozone will not be able to read any of the dtc for the trans or the antilock brakes. You will need a code scanner that is capable of scanning the extended codes like a tech 2 scanner from GM.

i havent replaced the trans just the engine

oops, haha my bad. If you manually shift the transmission, does it shift ok?

All is fixed it was the throttle position sensor. They ran the computer on it at autozone and came back low voltage so i changed em out and it works Better than it did LOL!! Thanks everyone for their help.....:smile: