LB7: SOS....Need HELP. Truck wont start

[Chevy1925]

I double and triple checked both. HAving another set of eyes on this yesterday really confirmed that I'm not overlooking the simple stuff like that. Every fuse that has power on one side, has power on the other. Confirmed multiple times by two people. And as far as the grounds go, every engine ground has been gone through. Some of the codes referenced come up with other chasis grounds that were not touched. Should I be going through the whole truck? Also, we performed this test by unpluging the alt and testing for 12v....there is nothing

but you have not checked the plug wires on the alt right? one is an excite wire that turns the voltage reg on and gets things going. if that wire is not getting power id find where the wire should be getting its power from and test there. im wondering if you may have damaged a few wires in the harness yankin the motor in and out.

if you do that, it will hopefully lead you to where the rest of the issues are coming from.

 

[duramax hd]

but you have not checked the plug wires on the alt right?

I checked for a 12v source coming through the wiring harness plug from the truck

 

[duramax hd]

James you are right. One of the two leads on the alternator plug turns the voltage regulator on and hence the alternator charges. Theres a lot more tech then that from what I gathered, but its something upstream of that either ECM related or BCM related. I am not ruling out that something may have gotten damaged in putting the motor in and out. It did blow that 40 amp fuse wich has me wondering. I just dont know where to start.

Heres a good article my buddy found that talks a lot about our charging system:
http://www.motor.com/magazine/pdfs/042010_09.pdf

 

[Chevy1925]

I checked for a 12v source coming through the wiring harness plug from the truck

i missed your edit lol. Looks like connector C2, pin 52 on the ECM is what sends power to the alt to get it charging. id dig down there and make sure all your connections are tight and test that wire to see if power is coming out of it with the truck running. the other wire is the signal wire that contols the batt light in the message center.

 

[MACKIN]

See if this helps at least you can trace the wires

 

[duramax hd]

Mack, really appreciate the diagram. We found this diagram pretty late last night after giving up. It shows the communication with the PCM and the data link system. But this is where I will try and pick up.

 

[duramax hd]

i missed your edit lol. Looks like connector C2, pin 52 on the ECM is what sends power to the alt to get it charging. id dig down there and make sure all your connections are tight and test that wire to see if power is coming out of it with the truck running. the other wire is the signal wire that contols the batt light in the message center.

Ill start there James and report back tonight hopefully. This is shown on the wiring diagram Mack just posted up. If no power is coming out of there, I look at pin 58 on the C1 Connector? That looks like where it comes in from the BCM?

 

[Chevy1925]

Ill start there James and report back tonight hopefully. This is shown on the wiring diagram Mack just posted up. If no power is coming out of there, I look at pin 58 on the C1 Connector? That looks like where it comes in from the BCM?

thats a data line. im not sure what kind of voltage can be seen there but if you have no power at pin 52, there is something going on in the BCM. Ben would be the best man to tell you where to go from there or someone else who better understands that side of the computers.

 

[duramax hd]

thats a data line. im not sure what kind of voltage can be seen there but if you have no power at pin 52, there is something going on in the BCM. Ben would be the best man to tell you where to go from there or someone else who better understands that side of the computers.

Ok cool. Ill start there. Never been more tempted to zip tie a portable battery charger on the front of something just to take it for a spin around the block. This has been contemplated

 

[Chevy1925]

Ok cool. Ill start there. Never been more tempted to zip tie a portable battery charger on the front of something just to take it for a spin around the block. This has been contemplated

lol just run a wire from the battery directly to the gray wire going into the alt (just scotch lock it on or pop the connector out and put a small spade connector on teh end of the wire to slide over the same blade the gray wire goes over) and go drive it . if you pop the connector out, the batt light will come on but dont worry about it if the wire is hooked up, the alt will be charging

just dont leave it connected with the truck off. I may fry the regulator if left that way for any long periods of time. as long as the truck is running, it wont hurt anything.

 

[hondarider552]

Any update on this Kris? Hows the truck running?