1997 grand am 3400 swap

[money_man]

we swapped a 3400 into a 1997 grand am that originally came with a 3100. It has very little power and stalls sometimes. it has a 3100 computer and transmission. The car also studders sometimes while excelerating and sometimes in park at idle the rpm's bounce between 750-1200. any idea's? we've talked to the guys at the dealership but they're stumped


tia

[IsaacHayes]

Swap the 3100's original injectors and Fuel Pressure Regulator back in. I bet you are using the 3400's ones and those are rated higher flow and so the computer doesn't know this and is running too rich and flooding out. That should fix it up.

Do this and if you still have troubles we'll go from there.

(Alternatively if you buy a DHP powertunr you could edit the stock computer to be calibrated for the 3400's injectors but that costs $$$ and if you don't plan on radically modifying the motor and just want it to run and be done with it, go with the 3100 injectors and FPR.)

[money_man]

we did change the fuel injectors, since they were different. im not sure about the fuel pressure relay, but i will find out and get back to you.

[money_man]

We tried changing the computer to a different 3.1, changed the fuel pump, changed map sensors plus alot more sensors with no change. Only thing we havent changed is the cat. the old fuel system we assumed worked completely fine although we could never drive the car with the 3.1 in it because of head gasket problems. It was dumping anti-freeze into the oil, so in went a 3400 which is supposed to be a straight swap. This is driving me crazy wondering what it could be.

[IsaacHayes]

Hmm. I guess it could be the cat. If you unbolt the down pipe and go for a short drive you can tell if it runs better. Don't drive too long or the heat can melt stuff.

BTW are you sure the 3100 was headgasket and not the common leaky lower intake manifold?

[money_man]

the problem with the 3.1 was they drove it too long with it leaking and the cam bearings were torn out of it. The diagnosis was made by the dealer.

We'll have to try he car with the downpipe disconnected so at least it'll eliminate the cat as a problem or confirm it.