1989 GMC Sierra fuel pump to feul pump relay and oil pressu

Tiny
UNCLE-D
  • MEMBER
  • 1989 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 255,000 MILES
Truck would start up and idle fine yesturday. But now when you turn the ignition to the on position the fuel pump does't come on, but the truck starts and idles fine. It also hesitates during normal accelleration, is the pump going bad or the oil pressure swicth cutting the pump out.
Tuesday, December 8th, 2009 AT 12:04 PM

3 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
The fuel pump should come On for 2secs. It starts up bcuz of the OPS when it senses oil pressure above 4psi it powers the fuel pump.

Check the fuel pressure with a gauge to rule the fuel pump/filter


https://www.2carpros.com/forum/automotive_pictures/12900_oil_sending_unit_and_fuel_pump_circuit_99.gif

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Tuesday, December 8th, 2009 AT 12:16 PM
Tiny
UNCLE-D
  • MEMBER
  • 2 POSTS
Truck wound'nt start this mourning, checked fuel pump fuse with trouble light, no light. Checked alcl g test light came on, haynes manual says bad oil pressure switch. Poured gas down tb truck fired up and stayed running, test lighted f/pump fuse ok now. Checked alcl g term no light. Oil pressure gauge does fluctuate quite a bit. Haven't checked fuel pressure yet don't have a gauge, can't get fuel filter off with out cuttiing lines to rusted. Any suggestions on why truck stayed running. Ussually dies after you dump soom fuel down the tb. Thanks for all your help razmataz!
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Tuesday, December 8th, 2009 AT 2:41 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check fuel pump relay and computer fuel pump control of the relay dark green and white wire, circuit no. 465
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Tuesday, December 8th, 2009 AT 4:21 PM

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