Thread: Engine swap done, problems

OK I own a 2000 Pontiac Grand Prix GT with a L36. I bought an engine and trans from a 1998 Pontiac Grand Prix GTP.

I swapped both in, engine and trans and are now having electrical issues. This is a run down of what the set up it. And yes everything is stock as far as I know.

1998 L67 engine, with 1998 L67 Trans-HD
1998 L67 engine wiring harness
2000 L36 engine fuse box (When running with the 98 Fuse box it dies soon after you start it)
2000 L36 inside harness (Swapped out BCM and DIC with the 1998 GTP)
1998 L67 GTP PCM

Front ABS are both not hooked up because we can't find the connectors. Its like there not on the harness.

Everything else is stock 2000 GT stuff, fuel pump and such.

This is the problems I am having.

Speedo does not work
Temp Gauge does not work
Tachometer does work
Alternator will stop charging the battery
Weird problem with the Low coolant light. When in Park and Netrual its on, once you go into Reverse it goes off.

...do you have all the sensors hooked up? sounds like you have the wire harness all goofed up.

Only thing I can think is you ****ed something up when splicing wires. Still don't know why people get the l67 harness, there's only two differences with it and the l36 (MAP and BBV)

Also, check that the ground wire on the trans is nice and tight. That can cause some funky things to happen when it's not

I'm pretty sure you'd find some differences in the grounds etc at the pcm or the main connector at the firewall. Gosh this post sounds familiar...didn't you post this same thing recently?

If I were in your shoes, I would swap the 2000 engine harness onto the motor and add the two wires for the boost control soleniod, then change the connector and extend the wiring for the map sensor. You have the wiring/connectors on the 98 harness. Then have someone load a 2000 GTP bin to your 2000 pcm and you are all set.

^ this.

use the GT PCM and wiring harness. add the connector for the MAP and leave the BBV vacuum controlled.

Why would I use the GT PCM? I have both engine and Trans from the 98 GTP in there, wouldn't it be better to use the GTP PCM?

Yea I read that, I just don't have anyone that can do that around here or have the money to send out to someone.

I have people telling me that I just need to use my harness, and hook up the GTP PCM and I would be good to go, then I have other people telling me I can't

Basically you have all the electrical components that are for a 2000 car. You are trying to make all these components work with 1998 wiring.

Instead of taking all these electrical components out and switching them of the dash and throughout the car, it is easier to use the same wiring (2000) and just add the connections or modifications necessary to make the BBV functional and relocation of the map sensor. Then by flashing a 2000 gtp file to your 2000 gt pcm, you will have the correct inj. flow rate tables and such to help the car run.

So I can't just have the 2000 wiring and have the 98' L67 PCM hooked up?

you probably can, but why when you could have used your stock pcm and get it tuned?

Because the PCM came with the car. I bought the entire car for 400 bucks. I have everything out of the 98 GTP. Just trying to find out what I need to do, either swap the outside harness back to the 2000 and hook up the 98 L67 or swap the inside harness to the 98 GTP one.

I know If I swap the inside harness to the 98 and put in the 98 Fuse box everything should work.

But I was hoping I can just change the outside harness back to the 2000 and hook the 98 GTP PCM up. I can do either just this one would take the least amount of time.

a top swap would have been cheaper and easier. im sorry youre going through all this trouble for the crappy gear ratios and lame low compression.

honestly the entire l67 swap should just drop in and work. i would correct the stuff so the setup is complete. the easiest for you is to put the old harness back on and rewire the MAP (and wire in the BBV if you really care to make it work right).

No my trans was totally screwed. Thats why I swaped both in, it was the easiest to do.

So I guess I'll work on swamping the 2000 engine harness back in and hook up the GTP PCM and hope for the best.

Ok well I swapped the harness, and most of all the problems went away.

The only thing left is for some reason the ABS+TCS lights are on, but I think it might be the connections at the wheel, didn't check over there really good before putting the wheels back on, this is last on the list atm.

Other thing that's still wrong is the Alternator is still not charging, no light though. I cheaked over the fuses and there fine, have been doing a few others to see if its a wiring issue before I pull it and do see if its bad. If it is bad, is there a chance that I can split the case haves and swap with the alternator internals out of my 2000 GT?

Last problem as of right now is a coolant leak, internal one at that. Its either the Supercharger gasket or LIM both I replaced and I'm thinking one or both didn't seal. Don't know what I can do to check on either or what to do to try and make them seal. And no the Supercharger gasket is not the Gearlock stuff, I did buy one of those but it didn't have the O-rings so I got another set from Advanced.

Thanks for any help

arent the alternators the same? couldnt you just swap them?

I think the alts are the same the bracket is different. Dont run your engine with a internal coolant leak.

I thought so too but there totally different, The brackets are different, but there molded to the case. That's why I was going to swap cases.


Also I'm thinking the coolant leak is the Supercharger gasket, seems alot of people have problems with it and knowing the luck I have its the same.

EDIT: Yes RTV is on the corners of the LIM gaskests, but that should have nothing to do with a coolant leak its mostly for oil. Also the LIM gaskets are the Alliumuin ones if that matters.

if the lim gasket is bad or not sealed properly you'll have a coolant leak. the gaskets are crush gaskets and need to be replaced everytime. oil goes into the heads, coolant and air travel through the lim, in seperate parts.

take the alternator to autozone or similar parts store and have them test it, its usually free.

the connectors at the wheels connect to the abs sensor and then connect again to the harness, each side is opposite so you cant screw it up.

i had some small problems when i did the swap and most of it was corrosion on my old wiring harness. i swapped with a 2000 gtp harness and was good to go. i also added the HUD and digital DIC by splicing into the wires, no need to change the BCM.

as far as tuning goes, i joined a local forum and had good luck with local guys helping me out when money is short. lots of good local deals on parts too