I have a 1995 4.3L vin "w" CPI blazer. It takes about 10 seconds to start when it is warm (worst after sitting for 5-10min). With the fuel pressure gauge hooked up, it will crank for 5-10 seconds with no pressure then suddenly the pressure jumps to 60psi and the engine starts and runs perfectly. I have changed the fuel pump relay and can hear it energize properly EVERY SINGLE TIME, however the pump will not always come on EVERY SINGLE TIME; always until 5-10 seconds after you start cranking. Like clockwork the engine will start and run when the needle jumps to 60psi but it takes so long for the pump to turn on despite the relay clicking on. I already pulled all my hair out and swore at it and that didnt do anything so please, please, please help me!

 

Bad check valve in the pump. Pressure bleeds off after you shut it down. next time , turn the key off and on several , just to the run position, don't start it. then after a few times try and start it .See what happens.

 

The next thing I would want to check is that there is actually voltage getting back to the pump. Once the fuel pump relay energizes, power should be sent right back to the pump and it should turn on. It is possible that the pump has weak starting torque, having trouble starting from a stop.

If you can, back probe the main power wire to the pump. See if the voltage reads properly when the pump is energized.

Does it change if you hit the bottom of the tank?

 

Haha I wish i could bang the tank but my Blazer has the optional armour plated grenade proof fuel tank skid plate. I am going to leave it overnight then probe for power as i crank and see if voltage is actually reaching the pump when the relay turns on.

Ok so i backprobed the plug at the pump, hooked up a test light and stethoscoped the tank as buddy cranked the engine and watched the fuel pressure gauge and felt the relay. This is what happened: The relay clicked on and then off to prime (no fuel pressure though) then the engine cranked for 10-15 seconds without starting and suddenly the test light lit up, the pump buzzed, fuel pressure spiked and the engine started. This truck works perfectly except for the delayed fuel pump engagement.

 

I'll have to try to remember to look up the wiring schematic when I get home. See if there would be anything between the relay and the pump that would prohibit the energizing of the pump. Off the top of my head, the only thing that I can think of would be the oil pressure sending unit.

Wiring Diagram:

 

So turns out there was a broken wire between the fuel pump relay and the splice where the oil pressure switch power feeds into the fuel pump power wire. So the relay would energize and feed power to the pump but the voltage never got there until you cranked long enough to close the contacts in the oil pressure switch. Hence the truck would crank too long but always start and run perfectly! Thanks for your input especially the last one.

 

Good deal! Glad to help!