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I have 2 '03 C4500's with dead LB7's...only 153k & 155k mi.
Thinking of swapping LLY's into both. (Have '05 C4500 w/LLY w/o any problems) All 3 have allison auto trans, no upgrades and do serious trailer towing...
Question is: will the LLY bolt right in? Other than ECM change, are there any other necessary components to swap?
BCM?
Harnesses?
ETC?
HELP!
 

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there is a BIG difference between an LLY and an LB7 and there is also some major differences between regular truck motors and medium duty motors and ECM’s.

im sure you could do it but it would be best to start with 4500 LLY’s …why not just rebuild the LB7’s I bet when you crunch the numbers the cost will be the same or lower the HP difference is not all that much and since your just towing performance is not the number one concern.
 

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If it was a 2500-- it would be so easy-- but like said- the 4500 block is different--! :mad:
 

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It can be done, I almost went ahead and pulled my engine out when the injectors took a crap. I found a complete LLY with computer and harness for $4500, plus it only had 7k on the clock.

Wife thought it was alot, until I told her the stealer charges $4800 to replace the injectors. But since I can do all the wrenching, it is only costing around $1350 to do the injectors. I say if they are blown, I would loo into doing the swap.
 

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I would like to hear from someone who has successfully replaced a LB7 engine in a 2001 – 2004 truck. I have a low mileage 2005 LLY engine on the ground, and a high mileage LB7 engine with bad injectors in my 2001 GMC truck.

What I know about engine swaps for these engines is that I have to take the turbo and exhaust pipes, glow plugs and controller, and the FICM from the LB7 engine and transfer them to the LLY engine due to structural and electrical differences. Then you must replace the wiring harness plug on the LLY injector harness to fit into the LB7 FICM. Then the ECU must be reprogrammed with different tables for the injector firing duration to compensate for the lower flow volume of the LLY injectors.

The big question is the longevity of the LB7 FICM which puts out 96 volts, and the LLY injectors that are designed to work on 48 volts.

Has anyone done this, and how long has it worked?
 

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you need to change the ECM, FICM and the engine harness along with the glow plug controller harness. you have the have the LLY engine style out of a 4500 and up series as the fuel filters are on different sides.
 

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To swap the ECU requires rewiring and swapping out the vehicle wiring harness and instruments, far too much trouble, but I have heard of using the LB7 FICM with the original 2001 truck ECU and connecting the LLY injectors to teh LB7 FICM.
 

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Please elaborate on the deadness of the lb7's

Engine will not start without ether, codes indicate low fuel rail pressure and balance test indicates bad # 4 injector. Engine oil level rises as the engine runs indicating further injector problems.
 
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