1999 Chevy S-10 fuel pump problems

Tiny
MARTINI77
  • 1999 CHEVROLET S-10

Electrical problem
1999 Chevy S-10 4 cyl Two Wheel Drive Manual 100k+ miles

I have checked all the fuses in the fuse box and they are working fine, but I am only getting 5volts to the fuel pump at the tank. Is there another relay that I need to check? If so where is it and how do I check it? If that is not the problem what is?

Do you
have the same problem?
Yes
No
Tuesday, September 9th, 2008 AT 8:06 PM

16 Replies

Tiny
RASMATAZ
  • MEMBER

Test the fuel pump relay or swapped it for a known good one its located in underhood fuse block.

Was this
answer
helpful?
Yes
No
-3
Tuesday, September 9th, 2008 AT 8:31 PM
Tiny
MARTINI77
  • MEMBER

Swapping out the relay did not resolve the issue. When I turn the key I get 12V to the pump for a brief period, but the pump does not activate. What can I try next.

Was this
answer
helpful?
Yes
No
Wednesday, September 10th, 2008 AT 4:40 PM
Tiny
RASMATAZ
  • MEMBER

Power the pump direct from the battery and tell me what happened.

Was this
answer
helpful?
Yes
No
-2
Wednesday, September 10th, 2008 AT 9:50 PM
Tiny
MARTINI77
  • MEMBER

I connected another battery to the pump and it starts working, could it be the connector at the pump?

Was this
answer
helpful?
Yes
No
-2
Thursday, September 11th, 2008 AT 5:50 PM
Tiny
RASMATAZ
  • MEMBER

Could be the connector test it or an open wire on the gray going back to the fuel pump relay.

Was this
answer
helpful?
Yes
No
-1
Thursday, September 11th, 2008 AT 6:32 PM
Tiny
MARTINI77
  • MEMBER

Well, I charged the battery replaced the connector at the pump. Using the new splices I checked the voltage at the wires. The combination that powers the fuel pump does not get any voltage to it. All the other combinations of wires get 12v for a second or two when the key is turned on, then all go to zero v except the purple/orange combination which gets 1.27v all the time. What can I try now?

Was this
answer
helpful?
Yes
No
-2
Monday, September 15th, 2008 AT 4:59 PM
Tiny
RASMATAZ
  • MEMBER

All the other combinations of wires get 12v for a second or two when the key is turned on, this happens bcuz the relay de-energizes

Test the ground wire to the pump-

Was this
answer
helpful?
Yes
No
-2
Monday, September 15th, 2008 AT 5:27 PM
Tiny
MARTINI77
  • MEMBER

Sorry to sound stupid, but I don't have a clue when it comes to auto electronics. How do I check the ground wire to the pump?

Thanks

Was this
answer
helpful?
Yes
No
-1
Tuesday, September 16th, 2008 AT 8:16 PM
Tiny
RASMATAZ
  • MEMBER

I connected another battery to the pump and it starts working, could it be the connector at the pump?

If it comes On then the ground is good.

Was this
answer
helpful?
Yes
No
Tuesday, September 16th, 2008 AT 9:28 PM
Tiny
MARTINI77
  • MEMBER

With the key on I connected another battery to the connections that power the pump, and it turned on. So that means it is grounded, right? What can I try next? Thanks for the help.

Was this
answer
helpful?
Yes
No
Wednesday, September 17th, 2008 AT 4:24 PM
Tiny
RASMATAZ
  • MEMBER

Earlier you said you got power for 2 secs at the pump-that's all you got before the relay de-energize-it should turn the fuel pump On for that 2secs.

If comes on by direct power from another battery-start it up and see what happens.

When you turn the key On the pump comes on for 2 secs just to prime the fuel system once it fires up the oil pressure sending unit powers the fuel pump constantly. see below


http://www.2carpros.com/forum/automotive_pictures/12900_oil_sending_unit_and_fuel_pump_circuit_73.gif

Was this
answer
helpful?
Yes
No
Wednesday, September 17th, 2008 AT 6:45 PM
Tiny
MARTINI77
  • MEMBER

I get a 12v reading on 4 of the 6 combinations of the 4 wires. One one combination I get 1.27 volts and the other connection I get 0v. The combination that gets 0v is the one that powers the pump. I am testing these voltages at butt connectors I used when I replaced the connection to the fuel pump. So the pump never turns on when the key is turned.

Was this
answer
helpful?
Yes
No
-1
Wednesday, September 17th, 2008 AT 7:20 PM
Tiny
MARTINI77
  • MEMBER

I connected the fuel pump to another battery and then started the truck. The truck started and ran until I disconnected the power to the pump. What can I try next

Was this
answer
helpful?
Yes
No
Thursday, September 18th, 2008 AT 5:32 PM
Tiny
RASMATAZ
  • MEMBER

Get the correct size wire and toggle switch hook up the pump temporarily from the battey in the engine bay. Till you can figure it out I've given you practically all I got. Don't forget to put the switch close by you inside-

It sounds as though the computer is not controlling the fuel pump relay control

Was this
answer
helpful?
Yes
No
Thursday, September 18th, 2008 AT 6:27 PM
Tiny
JCJONE01
  • MEMBER

I had a same problem. It turned out to be a bad fuel pump ground connection. The ground is located on the frame back by the rear bumper driver side. The self threading bolt was stripped out.

Was this
answer
helpful?
Yes
No
Sunday, November 9th, 2008 AT 4:53 PM
Tiny
PERCHERON1
  • MEMBER

What you are describing may not even be an actual "problem". My 1990 S10 gave me the same thing. I discovered that the system is actually designed to do that! The fuel pump relay is supposed to only energize the fuel pump for a few seconds to pressurize the fuel system so that the engine has enough fuel to start, then shut off. It then transfers control of the fuel pump to another relay. This relay is activated by an oil pressure switch. When the engine actually starts, engine oil pressure signals the second relay to again send 12V to the fuel pump for continued operation. This is a safety feature to protect the engine. If you suddenly lose oil pressure, the fuel pump is shut off, stopping the engine, to prevent burning up the engine. I figured this out after some research and studying the electrical diagrams. If the fuel pump runs fine with 12V hooked directly to it, the pump is most likely OK. A check of the fuel pressure to ensure that it is not weak, would still be a good idea while you are at it!

Was this
answer
helpful?
Yes
No
+2
Friday, January 15th, 2010 AT 11:04 PM

Please login or register to post a reply.

Related Fuel System Pump Fuse Questions

Recommended articles