Fuel pump not pumping

Tiny
LOU FLORES
  • MEMBER
  • 1987 GMC S15
  • 2.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 8,635,900 MILES
I can not hear pump when key turned on. How do I test Fuel pump relays that are in the engine compartment? I see three of them I do not know which one or how to test. I have Haynes repair manual but not much there on subject. Thank you in advanced.
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Thursday, December 29th, 2016 AT 2:17 PM

9 Replies

Tiny
CARADIODOC
  • EXPERT
No one "tests" relays. Even if you went through all the work to set up a test circuit, the contacts often are arced or pitted and will appear to work when there is no load on them, but then fail in the vehicle when they need to pass a high current. Instead, just swap the suspect relay with one of the other ones like it.

A better test is to bypass the fuel pump relay, then observe if the pump is running. I do not know if you have GM's older-style four-terminal relays or their newer Chrysler style with five terminals. The easiest way, until you tell me which you have, is to pop the cover off the relay, reinstall it that way, then squeeze the movable contact. When you release it, if you see a spark between the contacts but the pump was not running, the motor is likely shorted or the bearings are tight. If there is no spark, there is a break in the circuit that we will need to find.

If the pump runs when you squeeze the relay contact, have a helper turn on the ignition switch while you watch if the contact clicks for one second, and again during engine cranking.
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Thursday, December 29th, 2016 AT 2:44 PM
Tiny
STEVE W.
  • EXPERT
Check the ECM B fuse in the panel, it feeds the pump through the ECM.
If it's OK, Look for a tan wire with a white trace on it near the under hood fuse block or wrapped in the harness near the fuse box. That is a fuel pump bypass wire, Take a jumper wire and connect that to battery positive and to the tan/white wire. If you hear the pump start running, the relay or it's control wire is bad. The relays on them tend to get hot and fail.
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Thursday, December 29th, 2016 AT 5:38 PM
Tiny
CARADIODOC
  • EXPERT
Thanks Steve W.
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Thursday, December 29th, 2016 AT 5:47 PM
Tiny
STEVE W.
  • EXPERT
No sweat Doc, I've had a few of them over the years, pretty much every one ate at least one pump.
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Thursday, December 29th, 2016 AT 9:24 PM
Tiny
LOU FLORES
  • MEMBER
My Relays have four-terminal I will swap them and see what happens I thank all of you for your help.
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Friday, December 30th, 2016 AT 10:33 AM
Tiny
STEVE W.
  • EXPERT
Check the relay sockets as well. What happens is the pump will start to fail, it draws more current, then the connections in the relay start to pit and that increases the resistance. The pump gets less voltage and the current goes up more, then the relay socket starts to heat up and melt. After a while the relay plastic will actually melt into the contacts. When it cools off the plastic becomes insulation and your pump no longer runs.
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Friday, December 30th, 2016 AT 2:45 PM
Tiny
LOU FLORES
  • MEMBER
I swapped relays no luck I did notice signs of melted plastic on the relay socket. I would like to thank everyone for there help and advise I am going to purchase a new pump and relay.
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Saturday, December 31st, 2016 AT 12:18 PM
Tiny
STEVE W.
  • EXPERT
If you replace the pump be sure to replace the connector pigtail that powers it. Most of the pumps come with one but make sure you get it either way. One of the common items that starts the failure train leading to a failed pump is the connector getting weakened from the current flow. They redesigned the connector with larger contacts and better sealing. Try not to use the butt connectors they provide if possible, strip, solder and shrink tube is far better.
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Saturday, December 31st, 2016 AT 1:42 PM
Tiny
LOU FLORES
  • MEMBER
Thanks Steve W. I will do that to the new pump.
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Saturday, December 31st, 2016 AT 2:48 PM

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