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1991 V2500 with 4L80e, how do I control trans with PCM after LS Swap?

RockBottomRacing

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In my search for better MPG and more power, i’m about to acquire a parts truck (2003) with a 5.3. I’m looking for the proper way to use my factory 1991 PCM as a stand alone controller for my factory 4L80e. From some searching I’ve found others talk about how to do it while swapping in a trans, but I’m looking for some clarification for utilizing the stock trans and PCM. I was hoping some of you knowledgeable folks wouldn’t mind helping me figure it out :) I know about the flexplate/spacer/bolts and the ls swap mounts, and I’ll be using 2002 Camaro exhaust manifolds to clear everything, just trying to figure out the right way to control my trans. Any advice tips or links would be much appreciated! I’ll keep searching in the mean time. Thanks guys!

Oh and I’m going with a 5.3 strictly because I’m basically getting the whole parts truck for pennies, and because I plan to make this a daily/explorer truck, don’t plan to win races or tow heavy loads with it :D
 

sweetk30

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why not mod the harness for the extra wires for 4l60-e to 4l80-e and when the pcm is reflashed swap it to 4l80-e control .

this would save you a LOT of rework and extra stuff .
 

RockBottomRacing

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As in change the harness for the 2003 4L60e to work with the 4L80e? Would that also involve changing the trans internal harness to the new style?

I’m not opposed to that, I was just thinking in terms of saving money/ease of install, but I guess my understanding for the application is inaccurate?

why not mod the harness for the extra wires for 4l60-e to 4l80-e and when the pcm is reflashed swap it to 4l80-e control .

this would save you a LOT of rework and extra stuff .
 

sweetk30

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you would get a much better working relationship with both off the same computer . and any tuning work would be seamless .

have you looked around www.ls1tech.com . ? tons of info there .

but i am sure others will post up here with more than i can offer .
 

1-ton

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Did a 5.3 ever come connected to a 4L80E in 2003? If so an ECM/PCM from that combo should work. The only internal harness for a 4L80E you can buy is the 1993-up one because the early 91 to 92 internal harness had so many issues that they where discontinued completely. You more than likely already have the updated 1993-up harness in your 1991 4L80E because they had so many problems with them that your trans would not still be working with a lot of miles on it if it had not been changed. You can tell if your harness has already been updated by peeling back the wire loom protection running to your trans, and see if there is a bunch of crimped wires leading to your internal harness.
 
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sweetk30

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Did a 5.3 ever come connected to a 4L80E in 2003? If so an ECM/PCM from that combo should work..

dont matter like i said its a add a few wires and plug and reflash the pcm . guys do it all the time . i just have NOT done it my self yet .
 

1-ton

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dont matter like i said its a add a few wires and plug and reflash the pcm . guys do it all the time . i just have NOT done it my self yet .

I do not think you can flash an old OBDI/ECM/PCM. That have PROM's in them and not EPROM's. You have to burn those old chips, or modify it to run an EPROM, which a company called Moats can do.
 

Chevman88

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There are a few differences between 4l80Es throughout the years. The 91-92 had a different internal harness and pressure control solenoid, likely you have an updated harness because the old style would leak a lot. Either 96 or 97 changed the lubrication port locations to one in the front and one in the rear instead of both being in front. And then when LSs were introduced the trans came with a top bolt hole.

As long as you have the updated solenoid and harness you should be fine to retrofit the LS computer and harness to also control your 4l80e, just change the wiring slightly and update the tune. Otherwise you can use your existing computer as a stand alone controller, but I would need to dig through my notes to find the wiring diagram (had to do that when I installed an EBL flash on a one of my past trucks with a 4l80e). The best choice being to mod the LS computer to control both.
 
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