Purchased a 1999 Blazer 2dr 4x4 with 93000 miles for a work vehicle, have done some work to it and it runs great. However it is intermittently hard to start. Fuel pressure test shows 60 psi with key on, and 55 after 10 minutes. The problem is, as soon as I start cranking the fuel pressure drops down to about 40psi. Turning the key off and back on several times does will eventually get the pump to kick back on, but when I crank the engine the the pressure drops again. After 3-5 tries, the pump will kick on while cranking and it will start up and run beautifully with no problems. If I jump the fuel pump on the fuse block, it also starts up perfectly.

It had several problems when I bought it, missed horribly, but I have all those problems fixed except this one.
New distributor cap, rotor, plugs wires.
Cleaned mass air flow sensor.
New coolant temp sensor.

I have searched the forums here, but have been unable to find anything like this.
The closest I have came is a possible bad ignition switch,
possible passlock problem,
possible ground problem, though I would think that an intermittent ground would cause problems while running.

Any thoughts on this would be appreciated.

Thanks,

AJ

 

What happens to the voltage for the fuel pump at the fuel pump relay when pressure drops during cranking? Does it stay near 12V, drop or go to zero?

Try swapping a known good relay at the fuel pump location. If fuel pump power has a problem what is happening at the relay coil voltage?

George

 

I've swapped the relays around already, but I tried it again before I went to work today. Started fine this morning and at noon at break, but when I left work the problem popped up again. I had to stop at the auto parts store anyway, so I picked up a new relay and swapped it there. Happened again. Went to check the voltage after I got home, had the probes hooked up, 12.6, dropped to 11.6 when starting and it started every time. Could not get it to to happen. Put my meter in the cab so I can have it with me if it does it again.

It does tend to do it more after the vehicle is warmed up and has been driven a while though, which is why I originally thought it was the spider or pressure regulator, but after all the pressures have repeatedly tested within spec, I think I can rule them out.


I really don't like intermittent problems.