1990 GMC Sierra FUEL SYSTEM

READER6787

MEMBER
1990 GMC SIERRA
V8
4WD
AUTOMATIC
173,000 MILES

HI, My truck wouldn't start and I didn't hear the fuel pump run, so I replaced it. I tested the old one and it worked. Truck would not start after replacing the pump & I tested the new one before installing it & it worked. I wired the pump with a fused & switched wire and the truck runs, but doesn't have the initial high speed idle at start up, it runs fine once warmed up. Now that it is cold outside, it won't start unless I use starting fluid. I replace the fuel pump relay under the hood. How do I solve this problem?

Thank you

1 Reply

JDL

MECHANIC
16,098 POSTS

I don't know how you tested the pumps, a no load test isn't worth much. I've bench tested faulty pumps, using jumpers to a battery, it ran up a storm. Just wouldn't make any pressure. The brushes were wore down to the nubs.

You may have a hot fuel module that lets the vehicle prime a little longer than normal. I have no idea where it is located or if it might be causing your problem? As far as the fuel pump relay, you need voltage on the control and load side of the relay.

Koeo and cranking is battery voltage to the pump, engine running is alternator voltage.

Did you check for codes? Did you check fuel pressure? The computer needs to know if the engine is cold or hot.