Hi , I'm Ed from north Alabama. I just recently bought an 87 Gt with a rod knocking. It is the 2.8 with Auto trans. I am wanting to do a 3800 sc swap . I have found a series 3 from a 2005 Gran Prix with 120,000 miles on it. It is just the motor, Wiring harness has been cut when engine was pulled. i have searched the forums and see that i would have to run it as a series 2 and change tb. My question is what do I need get the auto transmission ,wiring harness series II PCM from.

Why not keep it as a series III. You'll have to replace your accelerator pedal for an electronic version to work the series III throttle body. Find a ECM and tranny from a Series III as well. You'll need a custom harness, built by others on this forum, to make everything work.
I did the Series II with 4 speed conversion. It was a piece of cake. "A child could do it".
Others will chime in, hold your hand and walk you through along the way as needed.

Spoon
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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 11-18-2023).]

We've done a couple of Series 3 swaps but always used the N* throttle body that is cable operated. This required using the 2003 PCM to shift the tranny. No earlier PCM will shift the 03-up transmissions. So in essence we used Series II control.
As Charlie said you could do a full series three swap using the accelerator pedal module and keep the electric throttle body but some serious reprogramming of the PCM might be required. The later 3800 systems were used in conjunction with traction control and I believe wheel sensors. I don't know if that's the best route to performance but a good programmer should be able to help you with a work around. Good luck on the swap, you'll love it.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Might be a dumb question but are your saying it has to be a 2003 pcm. So a 2000 or 2001 auto transmission, ecm and pcm and wiring harness will not work with a series 3 motor

quote Originally posted by FerioEd: Might be a dumb question but are your saying it has to be a 2003 pcm. So a 2000 or 2001 auto transmission, ecm and pcm and wiring harness will not work with a series 3 motor

If you have a 2000-2001 4T65e-hd trans, you can use the series 2 wiring harness and PCM with the series 3 engine.

You should use a cable operated throttle body with the setup.

Contact me via PM for more details and information.

[This message has been edited by olejoedad (edited 11-20-2023).]

quote If you have a 2000-2001 4T65e-hd trans, you can use the series 2 wiring harness and PCM with the series 3 engine. You should use a cable operated throttle body with the setup. Contact me via PM for more details and information.

Ok Thanks. PM sent (I think)

quote Originally posted by FerioEd: Might be a dumb question but are your saying it has to be a 2003 pcm. So a 2000 or 2001 auto transmission, ecm and pcm and wiring harness will not work with a series 3 motor

If you did not get the 4T65E auto trans from the same 2005 Grand Prix you got the series 3 engine from, then NO, you do not necessarily need a 2003 PCM. You only need a 2003 PCM if you are using a 2003-up 4T65E transmission, due to some electronic changes GM made in 03-newer 4T65E transmissions.

If you end up using a 2002-earlier 4T65E trans, you can use a 97-02 PCM (although I would avoid using a 97 PCM specifically due to some issues those PCMs had as well as their rarity.)

In any case if using a 2003-earlier PCM with a Series 3 engine, you will need an adapter plate that allows you to substitute a cable-operated throttle body in place of the Series 3's stock drive-by-wire unit. ZZP and a few other vendors sell such plates.

-Ryan

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[This message has been edited by Darth Fiero (edited 11-22-2023).]