thanks for looking!
I have asked this on other boards but didnt get the answer I want and since you guys program the proms then someone should know how the computer works. Here gos. On an efi system the injector s provided with 12v to one wire and the other is ground, which is switched or grounded by the ecm right, which circuit is it that the ecm gets its ref. signal from to know when it is supposed to ground the injector? Im trying to diagnos a no start in a tbi system ecm#747. With the harnesses unpluged all wires have power to them, red and white (12v supply) and green and blue ( ground) with it connected only the red and white have power? Whats weird to me is that if the ecm grounds the green and blue then how do they have power? I have gone through various books and texts with absolutely no help or explaination other than the obvious (noid light test) and that again one wire pos and one neg. Please Please help me Im totaly confused!!!!
Thanks in advace!!!!

 

In a 747, the ECM signals the ground side of the injectors. The red and white are fused 12V. See a wiring diagram at DIY-EFI
ftp://ftp.diy-efi.org/pub/gmecm/manu...47/747ecm6.jpg