3800 Engine swap question (lesabre to GP)

**1gr869** · 12-29-2010

Hey all,
Bought a black 98 GT with just over 103k. Ran beautifully and suddently threw a rod bearing (we think-haven't torn it completely down yet). Car is in good shape but obviously not well-maintained motorwise.

Found a 3800 from a 03 LeSabre with 1400 (yes 1400) miles on it. Installed new motor and a couple of sensors from the GP. Now getting Service Engine Soon light. Scanner said tranny code. Reset it and tranny shifted great until we got to our destination. Restarted car, engine light came back on and car would not shift out of 2nd. Shut car off, restarted and it shifted fine in all gears again, but engine light still on.

Could it be the PCM not recognizing some sensor in the tranny? I'm going to put the scanner back on it tonight to get the code.

**BoostnBlackGTP** · 12-29-2010

it could be your throttle positioning sensor. check that

**01gpgt01** · 12-29-2010

What trans and pcm are you using? 98 Pcm cannot work with a 03 trans and Vs versus. You will need a 2003 pcm. Also if it came from a lesabre Id think it has a 3.05 Gear ratio and not the 3.29 in your GT(not 100 percent sure)

If your still using the stock trans and stock PCM you need to swap out the maf sensor to your 98 if your using the 03's. They are different and the maf sensor will play havic on trans line pressure

**1gr869** · 12-30-2010

We are using the 03 trans with the 98 pcm. You say we need an 03 pcm. Would we need a GP pcm or a lesabre pcm? We were told by a couple of poeple that the 03 trans would work fine in the 98; only the gear ratio would be different. Can we reprogram the pcm with a tuner program?

The code on the scanner is P1810.

**Bio248** · 12-30-2010

the transmission is physically different from the rest of the 97-02 cars, you need the 03 transmission. gear ratios can be changed via a tuner, but it might be easier for you to just start with the right pcm for the transmission.

**1gr869** · 12-30-2010

So again I need to ask...do I need a PCM for an 03 lesabre or an 03 grand prix? I assume I need a grand prix for it to work with all of the other electronics but we know what assuming does...

**Bio248** · 12-30-2010

you need the right PCM for the transmission. both will work with the interior crap.

**1gr869** · 12-30-2010

Okay, thanks! The search has begun...

**1gr869** · 12-30-2010

Another question...

Will the 03 PCM connect the same as the 98?

We tried to put an 96 GTP computer in a 95 GTP and the connections were totally different. Now we have a 96 computer laying around.

**2003 SSEi** · 12-30-2010

the connections are the same on the PCM

**1gr869** · 01-08-2011

Ok, bought an ECM from an 03 LeSabre. The car started but stalled right away. The dash lit up like a christmas tree with dummy lights. Now what? Find an 03 GP ECM?

**1gr869** · 01-19-2011

Update - Bought a 01 Grand Prix PCM and got different codes. P0412 and P0418 (or something like that). Returned that PCM when I found out the salvage yard got in a 03 Grand Prix PCM the following week. Swapped for the 03 GP and BINGO! No codes, no dummy lights, and motor runs like a motor with 1400 miles should! Posting this for someone who may run into the same issue!

Thanks for replying to my posts, guys! I appreciate the help!

Thread: 3800 Engine swap question (lesabre to GP)

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