Fuel

Tiny
SCOTTMAY
  • MEMBER
  • 2002 OLDSMOBILE BRAVADA
  • 4.2L
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 140,000 MILES
No power to fuel pump power is at relay and times out in 3seconds but is not at the pump.
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Saturday, January 2nd, 2016 AT 10:00 AM

7 Replies

Tiny
CARADIODOC
  • EXPERT
Do you have voltage at the fuel pump during those first three seconds, or do you hear the hum of the pump? What is the problem you're trying to solve?
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Saturday, January 2nd, 2016 AT 10:19 AM
Tiny
SCOTTMAY
  • MEMBER
No voltage at fuel pump for the first 3 seconds or after.
I thought the full pump was bad I let the car set for some time do to a power steering leak on one of the lines I went to start and it only ran for a spit second and stalled if I spray starter fuid it runs I thout it was out of gas but it was full. After a few times trying it ran and into the garage it went replaced hose for steering and now it will not start again no fuel at test port and no power at all at fuel pump.
I had to drop tank to check voltage at pump so I took pump out pump works on bench but no power at plug.
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Saturday, January 2nd, 2016 AT 11:00 AM
Tiny
HMAC300
  • EXPERT
Check for mouse-it is they love to chew wires in vehicles also items in pic.
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Saturday, January 2nd, 2016 AT 12:00 PM
Tiny
CARADIODOC
  • EXPERT
First of all, are you aware there should only be 12 volts to the pump for about two seconds after turning on the ignition switch, then it will go back to 0 volts? That voltage will only come back during engine rotation, meaning cranking or running. The Engine Computer knows that by the signals it receives from the crankshaft position sensor and / or the camshaft position sensor. Most likely those are working because they're needed for spark too, and you must have spark if the engine will run on starting fluid.

Feel the fuel pump relay to see if it clicks on and off when a helper turns on the ignition switch. If it does, the control part of the circuit is working. Remove the relay, then use a test light to check for voltage. You should find 12 volts all the time on one terminal in the socket. Be careful to not stick the probe in too far that it stretches the terminals. That is big cause of intermittent operation or relays on GM vehicles.

If you find 12 volts on one terminal, it should appear on the terminal diagonally opposite that one when the relay turns on. You'll need to test for that voltage with the relay lifted just enough that you can get in there with the test light's probe, or you can stick a thin piece of wire into that terminal to provide access for this voltage test. You should see 12 volts there for just one or two seconds after turning on the ignition switch, then again during engine cranking.

Let me know what you find up to this point.
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Saturday, January 2nd, 2016 AT 12:12 PM
Tiny
SCOTTMAY
  • MEMBER
I did all the checks as you explained. I do have one prong of 12volts on all the time and when I turn on ignition I get 2 seconds of 12volts.
If I check the same way at the pump terminal plug with the light meter gray wire and black wire as ground. I get no 12volts for 0 seconds.
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Saturday, January 2nd, 2016 AT 12:44 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. That means there's a break in the gray wire or a bad ground. Don't overlook HMAC300's comment about mice.

I don't know if this applies to your vehicle, but in the '80s and '90s, GM had a lot of trouble with bad grounds on very rusty vehicles with metal gas tanks. The ground was made through the straps, not a wire to the body or frame. If you have a plastic tank, don't worry about that. Your ground wire will go to the body. If you have a metal tank, move the ground clip for your test light to a paint and rust-free point on the body sheet metal or frame. Do the two-second test again. If you find 12 volts now, there's a break in the ground circuit. You can verify that by probing the tank with your test light. (Ground clip is still on the body or frame). If the ground is broken due to rust, the test light will light up but a little less than full brightness during the two-second test and during cranking. Any voltage on the tank proves there's less than a perfect ground circuit.

If you still don't have 12 volts, there's a break in the gray wire. I've heard many stories where GM runs wires to the rear under the carpet on or near the transmission hump in the floor, and a lot of people find wires rubbed through there.

A lot of people want to run a new wire to replace the broken one, but I never allowed my students to do that. Reason is you don't know where or why it broke, so you can't make an informed decision as to whether another problem is going to occur soon with one of the other wires. This is true of a mouse nest too.

If the original wire is not cut off on both ends, where it's broken can rub through and short to ground. If the wire broke because it's under your feet and has been rubbing back and forth, or it got cut from laying on the sharp edge of a metal bracket, how long will it take before the next wire does the same thing? You need to find the location of the break so you can insure the same thing doesn't happen again.
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Saturday, January 2nd, 2016 AT 4:17 PM
Tiny
SCOTTMAY
  • MEMBER
Thanks for the help. I will do that.
Scott
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Saturday, January 2nd, 2016 AT 7:36 PM

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