[old_master]

[quote=Blue Bowtie]

Not to start anything, but that is a common misconception, and was once errantly taught even in factory service technical training. If you study the schematic for your GM vehicle, you'll discover that the auxilliary oil pressure switch is not in series with the fuel pump relay, but in parallel. This has been and continues to be the case for all domestic GM control schemes from 1982 EFI systems to the present. This means that it is not a "safety shut-off" as many people believe, but is merely a redundant path for pump power in the even of a relay or other pump power control circuit problem.

I studied the schematics closely, and noticed that on the fused side of the ECM fuse, which is hot at all times, there is a splice. One wire feeds the fuel pump relay, the second wire feeds the auxiliary side of the oil pressure switch then directly to the fuel pump, a parallel circuit. I service a fleet of Astro/Safari vans, and of the three I have tested so far, a '96, '98 and '02, every one remained running after disconnecting the fuel pump relay. This proves your theory of a redundant, or back up circuit. However, all three also stalled after disconnecting the oil pressure switch, (with the fuel pump relay connected). What all this means is that the ECM is programmed to shut off the fuel pump relay trigger circuit after the engine is running. By doing this it allows the oil pressure auxiliary switch to control the fuel pump. It also explains why the fuel pump continues to run after the key is turned off for a few seconds until the residual oil pressure bleeds off. I can't say what the results will be with other year vehicles until I test them, but I will edit this post as I find out. Unless I have 3 ECM's with the same problem, the oil pressure switch is in fact a safety shut off. It is possible that some ECM’s are/were programmed to leave the fuel pump relay energized after the engine is running. If that’s the case, it would bypass a perfectly good safety feature, and waste money on unnecessary parts doing it. Hmm, maybe that’s one of the reasons why they’re in financial trouble.