So I've had the 91 running several times the past few weeks. Moved it around under it's own power in the shop. Buttoned up a couple odds and ends tonight and was gonna take it out and up the road and back. Went to start it and didn't hear the fuel pump prime. No power at plug above the driveshaft with key on. Have battery power to the relay. But i have no power from the drive wire from ecm. I started it last weekend for my kid to hear it run and fired right up. Really annoyed tonight! Where do i go next?

 

ECM provides ground path on the relay control circuit, doesn't it? With key on, you should have power at two points in the relay socket. (one is battery, the other should be switched ignition.)

 

 

 

As shown below, for whatever reason GM brings the relay up for fuel pump, but almost every other relay down. Not sure why, but that banged me up when I made an engine harness for someone. Won't make that mistake again

 

Found my Haynes book and have that diagram. According to that there should be 12 volts coming from the ecm right? I have no power in that wire. Didn't yet pull the connector out to check it right off the ecm. Plan on doing that later tonight. I don't have, and haven't yet, had the ground wire from the engine to the firewall. Was just gonna run run from somewhere else on the engine. But it's been running like that for a couple weeks. The ground wire coming to the relay indicates good.

 

 

Don't laugh guys, found it Upon further inspection, and applying the KISS theory... realized i hadn't screwed the 2 grounds to the fender by the fuel pump fuse!! Only had them stuck behind the fuse holder! Screwed them against the fender and boom, power!!