2001 Chevy C1500 LD 4.3 Fuel Pump Circuit

ktmlew · September 10, 2015

Have one with long crank time. Connected FP gauge and have zero pressure at KOEO/no prime. Crank for about 15=20 seconds and truck starts and run normally. 58ish PSI. Originally suspected fuel pump relay. Tested relay with relay buddy. OK. Tested for power & ground and control signals at relay center. All good. If you remove the fuel pump relay with truck running, truck quits. Control from PCM send 2.5 second signal to relay at KOEO. No pump action. You can feel/hear the relay click. Crank truck 15-20 seconds and it starts. I did NOT test to see if there is power at the PRIME pin but will next time i get a chance.

I'm confuzzled? :whattodo:

sneakypete · September 10, 2015

check for power and ground at the fuel pump itself. these were bad for a poor ground at g403. did you have power at the ubec connector c3 terminal f1 grey wire during prime and cranking?

ktmlew · September 10, 2015

check for power and ground at the fuel pump itself. these were bad for a poor ground at g403. did you have power at the ubec connector c3 terminal f1 grey wire during prime and cranking?

I didn't check. Rack was tied up and didn't feel like crawling on the floor. Should have just checked at the prime terminal. The fact the truck starts and then stalls when the fuel pump relay is removed should indicate the circuit from the relay back is intact? I can hear & feel the relay being activated at KO but the pump doesn't run to prime. I didn't look to see the strategy for what signals the pump ON when engine is cranked long enough. They used to use oil pressure switch as a backup. Will review wiring diagrams some more.

Buddy_M · September 11, 2015

Check the pin fitment close in the relay box using a similar sized pin. I had a truck just a couple years older than yours(98 K1500) tonite just before I left work that would randomly stall. Wiggle the fuel pump relay when it was running and could feel it click on and off. Took a small pick to get more tension on the offending pin sockets and cant duplicate the problem anymore.

sneakypete · September 11, 2015

yes you can check the prime lead and it will tell you if everything is kosher after the fuse block. as you stated, GM stopped using a oil pressure switch as a back up in the mid 90's. the fuel pump relay coil is fed power from the pcm. fuel pump strategy is 2 second prime when key on. check for voltge at the prime terminal . throw an amp clamp on the feed circuit as well. (scope would even be better). might have a locked up pump and I stated before if you can access the wiring to the pump check your power and grounds. I'd be surprised if you ground wasn't causing a voltage drop.