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Electrical Problem Or Fuel Pump Bad, Is There A Test...?

chatvmax

By chatvmax
in Ask A GM Technician

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chatvmax New Member

chatvmax

Posted
Posted

Electrical problem or Fuel Pump Bad,, Is there a test...??

1992 GMC Van V8 Two Wheel Drive Automatic 99,000 miles

 

I have a 1992 GMC 5.7 ltr V8 with 99,00 miles on her,, She always ran good and is well kept:

 

Issue: No fuel to throttle body:

 

Van was running great about a week ago, I parked her and came out yesterday to go somewhere,, She cranked but didnt even pop..

 

When I took the air cleaner off and put a little gas down the throat of the throttle body she starts and runs till the gas runs out,,

 

1: Checked Fuel Pump Fuse,, GOOD

2: Put a meter on one side of the fuel pump fuse socket and 12v is there,

3: replaced fuse JUST BECAUSE

also replaced the fuel pump relay...

When I unpluged the fuel pump wiring connector back at the tank and put a meter on the plogs,, between the black wire and the grey wire i get 8.6 gvolts comming from the van harness,, the battery is fully charged..

4: i put 5 gallons of gas in the tank and looked for leaks NONE

5: Disconnected the 2 fuel lines that go to the throttle body,, NO GAS comming out - ZERO, disconnect the fuel line Before the fuel filter and NO GAS,,

6: Important note: when I turn the ignition on the dash board fuel gague goes way past full till it hits some sort of stop,, then when

 

I turn ignition off the fuel gague comes back to about the full mark,,? ther fuel gague always worked before ..

 

NO rust or leaks looking from the bottom,, but the van is parked in the gas and really cant jack her up or anything::: when i rap on the bottom of tank there is plenty of gas in it... HELP !!

[email protected]

 

shouldnt there be 12v a that connector back at the fuel pump..?

 

again gas in tank, starts and runs if i poor gas into the motor and then dies,

NO gas comming out of the fuel lines to the throttle body,,

Isnt there a Ohm test I can perform on the fuel pump..? Or can I just connect a ground to the black wire going to the fuel pump and hit the grey wire with 12V from the battery to see if it pumps gas...?

bill190 Enthusiast

bill190

Posted
Posted

Being as all vehicles seem to be differently designed any chance they get to do so, and being the dangerous nature of this repair...

 

I would suggest going by the factory repair manual on this one.

 

With other vehicles I've worked on, the fuel pump does not turn on until the ignition is switched to start or the engine is running. Just ignition on will not power the pump. (I don't know about your specific vehicle.)

 

Then there were specific steps to take in the factory service manual for troubleshooting this... Do such and so steps THEN jump these two wires at such and so connector, then see if pump starts up, etc.

 

As to the fuel gauge, many times this is a part of the electric fuel pump. So a clue there. Does the gauge peg the meter with the fuel pump connector disconnected? If no, then probably fuel pump problem, but best to verify this with the shop manual. (Usually these would read nothing when disconnected, but I wouldn't be surprised if there are vehicles out there where it pegs with the lines open or disconnected!)

chatvmax New Member

chatvmax

Posted
  • Author
Posted
Being as all vehicles seem to be differently designed any chance they get to do so, and being the dangerous nature of this repair...

 

I would suggest going by the factory repair manual on this one.

 

With other vehicles I've worked on, the fuel pump does not turn on until the ignition is switched to start or the engine is running. Just ignition on will not power the pump. (I don't know about your specific vehicle.)

 

Then there were specific steps to take in the factory service manual for troubleshooting this... Do such and so steps THEN jump these two wires at such and so connector, then see if pump starts up, etc.

 

As to the fuel gauge, many times this is a part of the electric fuel pump. So a clue there. Does the gauge peg the meter with the fuel pump connector disconnected? If no, then probably fuel pump problem, but best to verify this with the shop manual. (Usually these would read nothing when disconnected, but I wouldn't be surprised if there are vehicles out there where it pegs with the lines open or disconnected!)

 

Ok,, I didnt get a manual,, I tried but couldnt find one local,,,,

and I followed all the fuel pump wires and cant seem to find any issues,,,

I did recheck the voltage on the 3 wire harness coming out of the tank there is zero ohms between the black wire and frame or chassie ,, so it is the ground,,

The center wire [ grey ] has 8.6 volts comming down from the harness side..? no idea why , i would think it would need 12 v... BUT i did keep the gas line OFF between the fuel pump to fuel filter so i didnt damage the pump if something was cloging the line and it did happen to pump gas,, and then i :

.. Ran a wire from the black wire going to the pump and ground,,

THEN i hooked 12v+ to the grey wire [ center ] wire going to the fuel pump and NOTHING,, no click, no gas pumping,, not a noise,,,..

 

Looks like pump is bad,, NO...???

 

so to be clear i disconnected the gas line between the pump and the fuel filter and grounded the black wire off the pump harness, and connected 12v+ to the center wire comming off the pump harness and NOT A CLICK or peep.. or gas.... ..

Im going to get a pump tomorrow,,, I drained all the gas i could get out of the tank tonight and hit all the strap bolts with penetrating oil..

sound like i am progressing in somewhat the right direction?

[ I understand that you cant give me a green light cause of "gas tank" work and its dangerous stuff,,, but how does it sound as a reality check in general...??

 

Thanks for taking the time to respond....

 

It would be a blessing to have a schmatic of this pump or the new pump.. i am a electronics tech,, not a mechanic :thumbs:

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