[68GMCCustom]

Ok guys...need some help!

Hoping I can find out something from the knowledge pool!

I have an '09 LY6 that I'm converting back to efi from it being carb'd for the last year. I have a custom built "stand alone" harness with ecm and tcm setup for a 4L80e. There is a 200-4r in place right now so the harness ends for the ISS, VSS, and 4L80e and not connected to anything tho the harness is connected to the tcm.

I have a wiring problem I think.......just not sure. I can apply power to my Walbro external fuel pump and it run all day and build 56psi at the fuel rail. Connect it to the harness and power up the harness....and the fuel pump cuts out within 2-3 seconds. I guess I should clarify...the fuel pumps relay kicks out...the primary relay for the whole system is still active...so its somehow tied to the pumps relay. The vehicle will not start...but a little starter fluid in the throttle body and it will try to fire up and run. I've drained off the fuel in the line so that tho old fuel isn't filling the fuel rails.

Oh.....and the harness builder and tuner are not the issue and not open for discussion. Maybe at a later date once the problem is found and resolved so that everything is working as it should. I don't want this to turn into a bashing thread!

I have swapped the relays and the fuel pump relay still cuts out. So....have I got a wiring issue that needs the harness removed and sent to the builder? Or is it possible that I have an ecm problem? How do I verify the injectors are firing?

Thanks in advance!