Thread: Someone stuffed a 3.8NA in a 3.4 car... now what?

Hello all,

Recently ended up with a 94 Grand Prix GT sedan.... I didn't know what I had gotten myself into, only that the car was free and had a clean title, body, and interior. After getting it, something funny struck me... the engine in the car is a 3.8L V-6 (block from a Camaro), whereas the badging on the side of the car dictates it would have been equipped with a 3.4 litre DOHC motor.

At some point someone has done an interesting and apparently well-thought engine swap, but didn't do a very good cleanup on their wiring job... using and stretching the original harness, removing pins from the ecu bulkhead connectors, and leaving everything sprawled out and without tape, flex tubing, or any other kind of protection.

The whole reason for the repair is an apparent electrical failure @ the transmission harness, causing it to stop shifting suddenly and to have first only without reverse. However, the wiring harness is so damaged and chopped up, it's hard to tell exactly where such a problem could be coming from.

Does anyone have a clue what modifications have to be made for a 94 GPX 3.4 engine harness and computer to operate a 3.8L? This is an N/A motor by the way, I haven't heard of many people doing such a swap, but any and all help is appreciated.

Bill S.

Originally Posted by dsmuts

What's a gpx?

It a slang term the local parts stores and mechanics use for a Grand Prix......... didn't realize that wasn't more widespread.

GPX was a name given to a Grand Prix concept car GM produced in the late 90's if I recall.
Thats about the only time I've heard GPX used other than from someone who has confused it with the "GTX' package SLP installed on the 97-03 Grand Prix

Originally Posted by LeadfootCJ7

I think you might be better off getting new harnesses from the junkyard or someone on a forum parting their car out. Once you get that, start modifying the wiring correctly as necessary.

That's kind of the direction I feel I'm going in. I have a wiring harness and good PCM sourced from the local salvage yard, $50.00. I've just got to figure out the differences in the programming and the wiring. I'm sure that can't be the most difficult thing in the world. The one thing that IS probably going to be difficult is, this car is an odd option package. It's loaded to the hilt with gadgets. I have no idea if that makes much of a difference for the PCM or the engine harness. Definitely going to be a project. If I can't figure out how to get this harness done, I'll just stick the car out front with a $500.00 drag away sign on it.

Thanks everyone for the input.... wasn't sure what I was going to end up doing with this mess!

then topswap or turbo it

Originally Posted by EJOUIE

I'm working on getting some! It's always very dark in my shop, but I'll try to get a few good ones under the flourescents tomorrow.

Originally Posted by danomite02

then topswap or turbo it

I'm going to pull the casting numbers tomorrow to find out the exact motor I have so I can get a PCM programmed to match. How detrimental is a top-swap on an engine that isn't designed to be supercharged? I'm not a performance guy, I'm just a fix-it, but somehow I forsee that engine having ring/valve issues if it was super'd like it is. (Unless, of course, it was originally supercharged, I guess the casting number will tell.)

Originally Posted by txslow6

Someone posted a few months ago looking for a car very similar to this. Said his buddy did the swap and was trying to find it. Let me do a search. I might be able to connect you with him.


Found it. Also sent him a pm with a link to this thread. Not sure if its the same one. He's looking for a 93GT, but crazy nonetheless since you don't see this swap very often.


http://www.grandprixforums.net/3800-grand-am-78777.html

That's wild... a 3800 swap on a Grand Am? I believe it, never seen such a thing but after messing around with this Grand Prix, it would be fun I'm sure.
Yeah, mine's a 94 GP.... Which I may add that some jerk installed command control ride on as well, I found out today....butt end drags the ground and front end looks at the sky.... that sh*t comes out and gets replaced with Cadillac ride control, if not just regular old McPherson struts.