fuel pump voltage

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fuel pump voltage

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fuel pump voltage - 9/24/2006 9:56:10 PM

twfinch

Posts: 3
Joined: 9/24/2006
Status: offline

My fuel pump won't run on my 99 suburban with 90K. I dropped the tank (literally, but my shop light cushioned the drop), and checked for voltage on the plug. It is only 5 volts. Is that what it should be? If it is supposed to be 12V, any idea's why it only reads 5V? Also, how do you get the lines off the pump? I figured I'll put a new pump in since the tank is down, but can't easily get the lines off. Is there some sort of tool needed? Tim

Post #: 1

RE: fuel pump voltage - 9/25/2006 11:27:02 AM

ZX1100F1

Posts: 2429
Joined: 8/1/2006
Status: offline

If you're going to throw parts at it, start with the cheap ones (pump relay) first and if that doesn't fix it then replace the pump.

To remove the fuel lines, they use a plastic collar quick connect fitting:
1. Grasp both sides of the quick-connect fitting. Twist the female connector 1/4 turn in each direction in order to loosen any dirt within the quick-connect fitting.
2. Use compressed air, blow any dirt out of the quick-connect fitting.
3. Squeeze the plastic retainer release tabs.
4. Pull the connection apart.

Use a few drops of motor oil to facilitate re-installation.

(in reply to twfinch)

Post #: 2

RE: fuel pump voltage - 9/25/2006 6:45:12 PM

twfinch

Posts: 3
Joined: 9/24/2006
Status: offline

Thanks for the input. After buying a fuel pump assembly today, I see that the voltage I was measuring when I got the 5V reading was the status plug (3 contacts). It appears, from looking at the pump assy, that the 4-contact plug is for the pump and the fuel level sensor. I didn't get any voltage out of those contacts with the key switched on. Maybe there has to be some resistance (other than that of my voltmeter), or maybe I didn't test the right two contacts. The relay (located in the engine compartment fuse box) is good (installing a new one did not solve the problem and you can feel it click when the key is switched on). Is there a fuel pump fuse somewhere else that might be blown? Anyway, I thought I would connect the electrical plugs to the new pump prior to installation in the tank and see if it goes on when I turn on the ignition. If it does, I think my problem is solved, if not, could it be a faulty regulator that is erroneously telling the PCM that fuel pressure is good and pump activation is not required? Does the pump cycle on and off to meet demands, or is it just on all the time recycling fuel back to the tank? Thanks in advance for inputs, Tim

(in reply to ZX1100F1)

Post #: 3

RE: fuel pump voltage - 9/25/2006 7:35:13 PM

ZX1100F1

Posts: 2429
Joined: 8/1/2006
Status: offline

99% chance that your fuel pump is bad, a very common problem.

Do not plug fuel pump unless it is in tank and submerged or it will cavitate and be ruined.

(in reply to twfinch)

Post #: 4

RE: fuel pump voltage - 9/26/2006 12:38:11 AM

twfinch

Posts: 3
Joined: 9/24/2006
Status: offline

ZX1100F1
Your were right, it was the pump. I had a real hard time getting the lines off, but finally did so. I put the pump in, connected the lines and electical, changed the filter, then tested it. It fired right up, so I reinstalled the tank. That was also a pain in the XXX since I still had about 10 gallons in there and had taken the rock guard off. The new pump is barely audible whereas the old one was fairly loud. Thanks for the advice on not running the pump dry. I new you were not supposed to run without fuel, but I didn't think a couple of seconds would matter. Anyway, I didn't want to take the chance given the $200 spent on the pump assembly. Thanks for the advice, Tim

(in reply to ZX1100F1)

Post #: 5