2000 Chevy S-10 fuel pump voltage

Tiny
ENESENGR
  • MEMBER
  • 2000 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 220,000 MILES
My 2000 chevy s10 suddenly quit running last week. Engine cranks but won't start, no fuel pressure. Fuel pump won't run; relay and ecm-b fuse check out ok, but grey power lead going to pump only shows 5 v on digital voltmeter, using either the black lead or the truck frame as ground. What could be causing this, and could this cause my fuel pump to not work at all?
Monday, November 2nd, 2009 AT 2:21 PM

6 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Welcome to the forum, did you check voltage circuit at the relay? Any fuses you checked, did you use a testlite and see if the fuse circuit was hot? If you know which terminal at the relay is for the gray wire, you can use jumper wire from battery voltage to that terminal, use inline fuse, the pump should run. Voltage to load side of relay is hot all the time. Voltage to coil side of relay should go hot with the engine cranking. There is the initial prime, but, I wouldn't worry about that at the moment.
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Monday, November 2nd, 2009 AT 3:40 PM
Tiny
ENESENGR
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Here's what I have determined so far:

> Both the ecm-b fuse and the fuel pump relay are hot, both receiving full 12 volts with ignition on or off.

>Fuse and relay both check out ok.

> Ecm-b circuit goes to the ignition switch and then to the fuel pump via the grey wire, but only delivers 5 volts.

> Grey wire will remain hot as long as ignition is on, even if relay is removed.

> Coil side of relay becomes hot when engine is cranked, and remains hot for about two or three seconds after stopping. This circuit terminates at upper left terminal of square plug on fuel pump, and delivers full voltage.

> Fuel pump does not run, even when full voltage is applied to grey wire.
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Tuesday, November 3rd, 2009 AT 1:47 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
If you have good voltage and ground at the pump and no pump action, suspect the pump.
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Tuesday, November 3rd, 2009 AT 2:29 PM
Tiny
ENESENGR
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Replaced fuel pump, still not working. Have full 12 volts at fuse and on both sides of relay, still only getting 5 volts at pump. Any ideas?
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Sunday, November 8th, 2009 AT 3:09 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
What color wire did you check voltage on, at the rear, engine cranking. Gray wire is voltage to pump motor, if relay is energized. Did you check the ground circuit? I did mention checking for good voltage and ground before replacing the pump. If the gray wire at the front has good voltage and big voltage drop at the gray wire at rear, replace gray wire from front to rear. You need to be sure before cutting or replacing anything. I can't see anything from here? I have to rely on what you tell me.
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Sunday, November 8th, 2009 AT 3:57 PM
Tiny
CURT1298
  • MEMBER
  • 1 POST
I am having the exact same problem. What did you do to get the fuel pump voltage problem resolved?
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Monday, January 18th, 2010 AT 8:30 PM

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