Need someone's wisdom out there please help if you can....
Overview/background
1998 Pontiac grand Prix GT, the 3.8L engine went out on me about 2 months ago. I purchased a engine/trans out of a 03 Buick Regal. I replaced both my old engine and trans with the new one out of the 03 buick regal. Engine runs perfect. I used the existing harness that was already on my pontiac, including the ECM (computer). I am having issues with the transmission. More specifically, will only sometimes shift beyond 2nd, AND ALWAYS shifts hard. Took it and got it scanned and it throws a P1810 code at me. I have the harness and ECM from the 03 buick regal. I thought that the ECM could be to blame for the shifting problems so I plugged in the ECM out of the buick regal and unplugged the battery to reset everything, car will not start. I am about to plug the old ECM in and see if it works.
Questions
1. I though that all of the 3800 series 2 engines NS cars had the same trans 4t65E, so I did not think it would matter if I mismatched... IS THIS WRONG? Should the 03 buick engine/trans work with my 98 grand prix wiring harness/ECM...
