3.4L to 3.1L interchange in 1992 Oldsmobile (engine swap)
 

We have a 1992 Olds Cutlass Supreme, it has a 3.4 in it and we would like to change it to a 3.1. We have had two other Oldsmobiles with 3.1 and they were much more reliable than our 3.4. Since it is my car my husband said he would change the motor to a 1990 model 3.1 that we already have out of a car that was wrecked. It has 80,000 miles on it. He wants to know if it can be changed and if so what needs to be done, such as change the wiring harness, computer etc. Thanks so much.

You got the 3.4 DOHC? Those are a royal pain to work on and the reliability is not so great. I'm all for the 3.1 MPFI. I too have had several and they are tough as nails, have boatloads of torque, and are very good on gas too. That engine with 80k is just a baby.

I am pretty sure the DOHC engine has other components that the 3.1 does not have (cam sensor at least). Also an issue would be the transaxle. The 3.4 uses a 4T60E which is electroncally controlled by the computer. The 3.1 uses a plain old 440T4 which is vacuum controlled. Some guys have done this if you wanted to use your existing transaxle, either with some other choice or chip, or a hacked chip.

But honestly, the 440T4 is more reliable, they are very tough. The 4T60E you have now is not that great, it has valve body issues, especially the early ones like you have. I think your best bet would be to swap in the engine, transaxle, harness, and ECM from the donor car. Keep the donor car till you're done in case you need any odds and ends. Both engine and trans will bolt right in, and should use the same driveaxles and mounts.

+1
what he said.

I have done several GM to GM swaps.
They are easy to do since most GM stuff is interchangeable.
Currently my son drives a 1994 Grand Am (factory Quad 4) with a gen 3 (2001 or newer) 3.1 in it. Everyone said it won't work and he thinks its the best car I ever built him. My biggest problem there was the cluster setup, I ended up putting individual sensors on the motor for the cluster to work right.

Don't look for problems, and yes, keep the donor till the swap is complete and you are satisfied with the results.

Have fun,

I've had two different GM's (Pontiac and Chevy) that have the 3.1 MPFI mated to a 4T60-E - I don't think you'll have any problem doing it. They DO have gobs and gobs of torque at low RPMS.