Hey I had a question I recently put a lb7 in my lly (the motor blew up and found a good deal) but I got the whole wiring harness and the ecm and ficm and everything I need. Only think I’m running from the lly is ecu/tcm and the air box. Just was curious if there is anything special that needs to be done. I have everything in there and tried to start it but it just keeps turning over but won’t start
04.5 LLY swapped to 04 LB7
- Thread starter Countryboy1101
- Start date
You can’t mix the ecm / ficm. And if you want to run the Lly ecm you’ll need custom tuning (that will need a lot of tweaking) to get it close. It will never run perfect that way.
I would use the lb7 ecm for your lb7, with the lb7 ficm.
I would use the lb7 ecm for your lb7, with the lb7 ficm.
Did the heads get hurt when the lly blew up? If not, I’d put the lly top end on the lb7 bottom and call it a day.
Rfletes79 i haven’t mixed anything up everything is lb7 except the TCM. My problem is when everything is hooked up the starter tries to run all the time when I turn on the key on so I’m just curious if there is anything special that needs to happen from the lb7 engine wiring to the lly BCM (body control module) sorry for the confusion guys
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Your op says your using the Lly ecm tcm and air box.... is this statement true??
What ecm and what ficm are you using?
What wiring changes did you do at the fuse box (Underhood)?
What yr lb7 did you use? Harness, ecm from that same engine?
What ecm and what ficm are you using?
What wiring changes did you do at the fuse box (Underhood)?
What yr lb7 did you use? Harness, ecm from that same engine?
Going to throw out a few ideas which might help. ECM controls the starter relay.
Inputs to the ECM. The BCM is the "power mode master" of all modules connected by the class 2 data bus. The BCM does monitor the ignition switch with 3 different signals, ACC, Ignition 1 and Ignition 0. From these 3 signals it determines which position the ignition switch is in and then sends the appropriate power mode commands to other modules. I included a picture of the FSM page describing this. If you know someone with a Tech 2, you should first check what state the BCM thinks the ignition switch is in. It will think the truck key is in START position if it doesn't see the accessory power but Ignition 1 and Ignition 0 are powered. Accessory power to the BCM comes directly from the TBC ACCY fuse which is powered from the ignition switch when it's in the RUN and ACCY positions. Upstream from the ignition switch, this circuit is fed from the 40A IGN B fuse. So check both of those fuses for starters.
There is also a CRANK signal sent directly to the ECM from the ignition switch as well through the 10A CRANK fuse. Check to make sure this is somehow not shorted to a +12v signal that's hot in the RUN position. I am not sure what happens in the case of a conflict where the ECM is not getting the CRANK signal via this circuit while the BCM is sending a START message, or vise versa.
Outputs from the ECM. The ECM grounds the starter relay when conditions are met for starting. Check to make sure this circuit (ECM connector C2, pin 4) is not somehow shorted to ground.
Finally - there could be a missed chassis ground connection somewhere.
2003 LB7 info below.
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Rfletes79 I’m using the LLY TCM and I’m using the LB7 ecm and ficm from the same motor I put in the truck it came with the complete wiring harness that is the ecm and everything only thing it didn’t come with was the TCM. Nothin it pretty much just plugged up I had to splice a wire in from the old wiring harness to fit in the fuse box and it’s a 2004
Maybe check the starter relay. It maybe sticking... swap it with another in your Fuse box. Also, what wire did you have to splice in the fuse box??
This should be a direct plug n play. No issues with your bcm, ignition etc. The only extra Steps needed after the swap and plugging all the lb7 stuff into your truck is a vats relearn and fuel gage recal.
How did you address the nsbu switch?? The lb7 harness is different then your LLY trans.
This should be a direct plug n play. No issues with your bcm, ignition etc. The only extra Steps needed after the swap and plugging all the lb7 stuff into your truck is a vats relearn and fuel gage recal.
How did you address the nsbu switch?? The lb7 harness is different then your LLY trans.
Ok I’ll check that and try it. Um I’m not exactly sure what plug it was it was a different one on the lly then the lb7 I can take pics tomorrow and post them then it was 3 or 4 wires (one plug) and that’s what I thought. And I had to buy the nsbu for the lb7
Could you verify the main problem you are trying to solve right now is that the truck starts cranking (but won't start) when you turn the key to RUN?
My suggestions were for troubleshooting "truck cranks when key is in RUN position". Failure to start is a whole other set of potential causes. Assuming we're going after the "truck cranks when key is in RUN", one of the easiest things to try is verifying if power is being applied to the CRANK fuse when key is in RUN position. Did you have a chance to check anything I suggested?
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