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I have had this LB7 from an 01 donor sitting in the shop to put in my 56, but just haven't gotten around to it and was tired of tripping over it, so we decided to put it in a Yukon XL. The Donor and the Yukon are both 01's. The motor and trans swap was really straight forward, mounted up with almost no modifications. Only thing we had to modify was the Trans cross member. Ran new rubber fuel lines from the tanks to the fuel lines on the motor with new quick connect ends. Wiring seemed to be pretty straight forward, but this is where im lost. I had the truck running in a standalone operation before the swap, just with the wiring harness plugged into everything. It would run from time to time, but you would have to mess with it. Now that it is in the Yukon, it started 1 time, but hasn't started since we killed it. It is throwing a P0340 and 0341, can clear the codes and the 0340 almost instantly comes back. I have changed both the Cam and Crank sensors, and still no improvement.

I do have 4 or 5 wires that I believe are block grounds just from tracing them out that I cut when pulling the cab on the donor truck. They are in the same bundle as the starter relay hot wire that runs to the starter from the main harness. I can wirenut the wires together (all black) and run them to the ground, and everything comes alive, but still no fire. Gauges all seem to be working like they should, ecm seems to be coming alive like it is suppose to, tcm seems to communicate ( no P0700 codes or anything), My EFILive V2 will talk to the truck (haven't tried to flash it yet). I have done a Relearn for the VATS and it seemed to have taken. The BCM from the diesel was toast I think, so it has the Yukon bcm in it now. The Diesel Cluster seems to be working properly.

What am I missing here? Is there something in the ECM that needs to be Tuned out to make this fire, or does it sound like the wires that were cut probally need to be traced out somehow and landed back to the appropriate ground loop on the block? If so, does anyone have a wiring diagram for this bundle of wires?

Sorry for my Long-windedness, just trying to understand the funk going on with this.

Any insight or suggestions would be greatly appreciated.

Thanks!
 

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They don't do too much LB7 work anymore. But they still do know their stuff. Did you disable the VATS with the Yukon XL BCM in the vehicle? If not you need to do it. Get on alldata.com if you need some wiring. Probably should start with the cut wires and ohm them out to make sure you're getting a good ground.

Also you may need to check your wiring for the cam shaft sensor to ensure good connections. If the ECM doesn't know where the pistons are, then the engine isn't going to want to fire. If the circuit and performace is bad it could just possibly be one of those grounds.

Also this i don't know, but is there a sort of relearn that needs to be done after replacing that sensor?
 
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