Gray Ghost Silverado

iTrader: (1)

Not entirely sure how to explain this, but my 07 NNBS Silverado was running great after the rebuild, then the fuel pressure began dropping off. So I stopped back at my house, killed it, and determined that something had gone wrong inside the fuel tank. I figured, no big deal, I'll just drop the tank and fix it. Went to go start the truck to drive it into the shop, and it wouldn't crank. I tried connecting to the ECM, and got nothing. So now I'm starting to worry.

Undid the battery's negative cable for 15 minutes, tried it again, then it read out, Service 4WD. Then the ABS light illuminated. Still refused to start. Cycled the ignition on and off quickly and on the fifth cycle it started, but the speedo didn't work, tach didn't work, oil pressure gauge didn't work, or fuel level gauge. The voltmeter however worked well. I dropped the tranny into drive and noticed it was stuck in 3rd gear. (Still couldn't access the ECM)

Pulled the truck in the shop. Killed it, back to the same thing.

So by accident I found I could connect to the ECM with HPTuners via the key being on ACC, but as soon as I turned it to run, it would disconnect the laptop.

I finally managed to pull out a C0247 code, and 4 different Lost Communication codes concerning the TCM, BCM, EBCM, and Transfer Case Control Module.

What in the hell happened?!

Thanks,
-Robbie.

62nalide

iTrader: (1)

holy $hit no way man

01WS6/tamu

iTrader: (36)

start by checking every ground on the engine. Then pull the UBEC and try resetting every connector in it.

2007 had horrible problems with the underhood power center with gremlins like you are stating and if you removed the ubec to undo the engine harness it could have awakend the gremlins.

When we have trucks come in with unexplainable gremlins we start by checking every single ground even at the battery. Usually everything is resolved once the UBEC fuseblock is replaced.

Just a place to start and be sure to check battery cables and use a DMM to see what the KOEO voltage at the battery terminals is reading. A dying battery can cause really weird **** too.

lady3bglover

iTrader: (3)

Holy crap Robbie ..

Idk, try swapping the puters?

Gray Ghost Silverado

iTrader: (1)

Ok, so I did a quick run over all the engine grounds and found that they're all nice and tight. Accounted for two on the passenger head, two on the drives side ground post at the front of the engine block, and one on the drivers rear cylinder head to firewall.

The battery is a near brand new Optima Red Top that shows a no load charge of 12.8 volts.

What I failed to mention is that I'm pulling two accessories right off the UBEC (Primary fuel pump pulling off the MISC IGN hun, and Intercooler pump pulling off the hot post in the front of the UBEC.) could I have overloaded something?

I know! Right?! I was so happy yesterday.... Then it died

01WS6/tamu

iTrader: (36)

Are you just operating the relay coil for the fuel pump off of the misc ign fuse. If so you should be fine. There is always the possibility the fuel pump is putting electrical noise into that ign power circuit and pissin off the computers. try disconnecting that and see what it does

Personally if it has never been changed I would go order a brand new underhood UBEC and I bet your problems will go away. Without being there to troubleshoot personally all I can do is throw ideas your way and see if I get close.

Gray Ghost Silverado

iTrader: (1)

Nope running 12 volts from the Misc. IGN source right to the pump. I tried disconnecting it, no dice. I finally got the engine to start again today and so I pulled the BCM fuse. Did absolutely nothing.

The UBEC has never been changed. SO..... I guess I'll put that on my order list.

Would you like me to make a video for you? Thanks for your help man.

RacinRust

Do you have any aftermarket relays or electrical equipment in the system. Have had the exact same problem with 08 NNBS after an engine swap and other mods. These damn things don't like ground feed back through closing coils on some aftermarket relays. They will throw a direct ground spike to the pos side and freak out the modules.
Just a thought. May want to try to isolate any added equipment. Then back probe the pin outs on the UBEC. Just my 2 cents.

Byrdman11

iTrader: (1)

Where is a battery connection to check/clean on the pass side big wire big problems I've seen with that one. Also clean ign switch for low voltage input and output.

Gray Ghost Silverado

iTrader: (1)

Yes, lots of aftermarket components. It is now a 417C.I. LS3, big cam, DoD and VVT delete, heads, and Kenne Bell Supercharger with a 50 shot. 4L80E mated to stock transfer case, blah blah blah. Dual intank 255's, I also unplugged the FPCM and ran new wire to the primary pump.

My own damn fault it appears, I ran the 12v constant source to the MISC IGN hub with an extended circuit. According to the wiring diagram, fuse 44 supplies wake up power to the auxiliary BCM. I think the additional load of the fuel pump getting hot in the tank took out either BCM or Auxiliary BCM. This fuse also supplies wake up power to the Transfer case shift control module. Even though it threw a code for losing communication with the TC control module, it will still shift from 2-4WD. So I assume this module is doing ok.

Is there a test you can perform on either module to see wether or not it is corrupt/inactive/broken?

Also I inspected the UBEC visually. There are no corrosion spots, nor hot spots or bubbles in the transistor field.

What do you think?
Will check ign switch voltage. Thank you.