A little over a month ago I was having problems with my 94 Blazer (4.3, VIN W) where it wouldn't start sometimes. The fuel pump was not coming on and pumping any fuel. I checked the pump by jumping power to the pump at the relay harness and it pumped up to 60psi every time I applied power. I checked the relay and every time I applied power the relay would close and there was continuity. The ground checked out OK and so did the 12v supply. I swapped the relay out with one from my old 94 Jimmy and ever since that time the Blazer started up reliably every time...

...until Friday. I was on my way to a gig in Eastern Washington and I stopped in Seattle to pick up the banjo player. I pulled into his driveway and shut it off after an hour of driving on the freeway. After packing up his gear in the Blazer I tried to start it. It cranked and almost started. I thought it was starting so I let off the key. It didn't start. I tried cranking a couple more times. No start. I popped the hood and switched the fuel pump and horn relays. Still no start. I switched them back and crawled under the back of the Blazer and listened for the familiar buzz of the fuel pump. The banjo player turned the key on and there was no sound of the fuel pump.

Having to get to the gig we repacked the instruments and gear in the banjo player's Ford Focus and headed over the mountains. Sunday morning when I returned to Seattle I loaded my stuff back in the Blazer and it started right up. It's started every time since then. I haven't tried to restart the Blazer quickly after an hour-long freeway drive yet. Most of the trips have been small, short trips close to home.

How do I troubleshoot this? It wouldn't start on Friday when I switched relays which would seem to indicate that the relay is not the problem. The two things I'm thinking are some kind of problem with the pump itself or a problem with the oil pressure sensor. Give me your suggestions.

 

How is the socket that the relay fits into? Is there any corrosion? Do all of the terminals look good? Do they fit tight? I have seen it a few times where the terminals get spread and loose contact.

Another tactic would be to smack the bottom of the tank. If that causes the pump to come to life, then the pump is on its way out.