swap 4.2 for 4.2 with gears

[BlueC7]

Looked at tons of posts but not finding what I need, Have 03 TB LT engine w/ knock(surprise) at 140K. I found wrecked 03 LS doner with 70K and runs great. LS has 373 gears as mine has 342s., if I swap out the engine/trans/transfer case and rear diff. from the LS will I need to swap the ecu/pcm from it to make the speedo and engine tune work correctly? Would love to have the lover gear.
Thanks

 

[TollKeeper]

Swap everything over except the rear diff. Should all be plug and play!

Otherwise, you would have to swap the front and rear diff, and then have the PCM sent out to be reprogrammed. I think @limequat can do that?

 

[BlueC7]

thank you, my thoughts were and correct me if I am wrong. I would swap the (drivetrain)engine, trans, transfer case and rear in to mine so I could end up with the 3.73 gears. I dont know if I can then swap the PCM out of the doner TB to make everything work so computer is happy and speedo is correct

 

[TollKeeper]

No you cant. Each module in your truck is VIN coded. Each time you start the truck it checks for this. So no VIN will match. You would have to send out your PCM, as stated earlier, to someone that can reprogram for the GT4 axles, and delete the GU6 axle code, or however that is done.

 

[BlueC7]

Ok thank you that is the info I needed. is the vin code it looks for in the body control module, how does it know? just curious

 

[TollKeeper]

Its in almost every module. It has a LAN (network like your work/home), and each computer talks to each other. SRS Module, BCM, ECM, TCM, TGM, DDM, PDM, ICP, etc. Some save a VIN, some dont.

Some cars have as few as 1 module, some cars have an unprecedented 37 (highest I have heard so far. Benz or BMW if I remember correctly. Some cars even have a ECM for each side of the engine (VW W12, Ferrari, Lambo).

 

[Mooseman]

Hold on. Yes he can. VIN mismatched to BCM will work after a security relearn. Have swapped PCM's regularly with a mismatched VIN and it will work.

What you will need is to also swap the front diff aong with the rear diff. They are a matched set. And yes, you will need to swap the PCM to the one with the 3.73 programmed in it to have proper speedo readout.

So yes, your plan to swap everything from the LS to your LT will work. Use the LT's PCM after a security relearn.

 

[BlueC7]

So yes, your plan to swap everything from the LS to your LT will work. Use the LT's PCM after a security relearn.

Thank You, do you mean use the LS PCM right because it has the code for the 3.73s?

 

[TollKeeper]

@Mooseman - I stand corrected, I didnt think it was that easy.

@BlueC7 - So you would use the PCM from the truck that the drivetrain is coming from, and swap it all.

 

[BlueC7]

Thank You Tollkeeper and Mooseman for all of the help!!

 

[Mooseman]

Thank You, do you mean use the LS PCM right because it has the code for the 3.73s?

Got confused between the two. Yes, use the PCM that was programmed for the 3.73.

 

[BlueC7]

The relearn is the 11 min./ 30sec. deal 3 times right?

 

[limequat]

Yup the 3.73 PCM is the way to go.
1) Speedo will be correct (this can't be correct otherwise on a 2002-2005 PCM)
2) No need for CASE Relearn

 

[Mooseman]

2) No need for CASE Relearn

That's right since the PCM is following the engine.

 

[HARDTRAILZ]

Yup the 3.73 PCM is the way to go.
1) Speedo will be correct (this can't be correct otherwise on a 2002-2005 PCM)
2) No need for CASE Relearn

Apparently it can be corrected with $110 add-on thing according to a post on facebook with video. He is supposed to be doing a full write on fit.