1989 Chevy S-10 fuel delivery

Tiny
PATRICKMULCAHY
  • MEMBER
  • 1989 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
Fuel pump relay is not being activated by the computer. I've checked the pump, relay and disconnected the oil sending unit but still no signal to the relay for operation. My relay is good, my pump is new but for some other reason the computer has shut down the pump. Any suggestions?
Monday, October 18th, 2010 AT 6:31 PM

6 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Check the ecm B fuse for voltage, use a voltage tester. With an oil pressure switch wire in parallel with the pump relay, if that switch is functional and has voltage, the computer can't stop the pump from running. Once you crank it enough to bring up oil pressure and that switch closes, the pump will get voltage, regardless of the relay.
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Monday, October 18th, 2010 AT 6:41 PM
Tiny
PATRICKMULCAHY
  • MEMBER
  • 3 POSTS
All fuses show power, I'm uncertain about the parallel instructions you gave. I'm not familular with an oil pressure switch. I also am not sure how the fuel pump relay is switched, whether with power to the green/wht wire or ground to it accually activates the gray wire. I do understand the oil pressure can shut off the relay but I don't know how. Can you elaborate further? Thank you for your time!
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Monday, October 18th, 2010 AT 7:53 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
In this application, oil pressure switch in the fuel pump circuit, oil pressure can't shut off the relay.

The relay has two circuits, the coil side of relay and the load side of relay. The pcm supplies voltage, green wire with white tracer, to coil side of relay during initial prime and if there is an rpm signal, voltage continues during crank and run. The ground for coil side of relay is constant. When the relay is energized, the arm for load side switches to voltage which is hot all the time, ecm B fuse. The o/p switch and load side of relay gets voltage from the same fuse.
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Tuesday, October 19th, 2010 AT 8:56 AM
Tiny
PATRICKMULCAHY
  • MEMBER
  • 3 POSTS
I'm not getting power to the grn/wht wire at all and when I bypass the relay and power up the fuel pump my injectors aren't opporating. This is why I think something has shut down the system. Any suggestions? I've looked for a trouble shooting guide but haven't found one.
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Tuesday, October 19th, 2010 AT 6:05 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Sounds to me like more than one problem. You should have fuel pressure, engine cranking, even without the the relay. If no injector pulse, engine cranking, check rpm signal. As far as the fuel pump, the rpm signal has nothing to do with the initial prime.
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Wednesday, October 20th, 2010 AT 9:17 AM
Tiny
PATRICKMULCAHY
  • MEMBER
  • 3 POSTS
There's no rpm gauge, do I gauge the coil like I used to or how else do I check the rpm signal? Also, I doubt it has more than one problem, the driver said the car stalled while cornering a few times then died. This car belongs to some friends from church and I normally take care of simple issues. This problem has tried my patience.
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Thursday, October 21st, 2010 AT 8:11 PM

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