I have a 96 Blazer 4.3 4x4. When I got the truck about 8 months ago, it ran kinda rough, almost like it wasn't getting enough fuel pressure, but I never had any major issues with it. About a month ago, I drove it about an hour, left it sit for a couple, drove it about 20 minutes, and then it died. No fuel pressure at all. I assumed fuel pump, so I dropped the tank and replaced the pump. It ran really well (no rough idle at traffic lights, lots of power, etc). Then about 6 days ago, it died again, no fuel pressure. I let it sit for about an hour, and it ran again, but it ran rough like it did before replacing the fuel pump. I drove it the next day, got to work, and got almost all the way home and it died again. Letting it sit for about 2 1/2 hours and it started and ran again. Even now it will run, but obviously I'm not trusting it at this point. I have checked everything I know to check (fuel pump relay, fuses, etc), and the only thing that seems strange to me is the voltage on the wires on top of the tank. The fuel pump harness wire has 3 wires, Black, Green, and Gray. The green and gray are both reading 5v as soon as you turn the key on, and remain 5v until about 10 seconds after you turn the key off. I was under the impression they should read 12v, and that with the key just set to run, after 2 seconds the voltage on the pump should drop to 0v, am I wrong in this?

Some other information that MAY be relevant:

* Air Bag light has been on since I bought the truck
* ABS light came on about 2 weeks before the first time it died (before replacing the fuel pump), but it needs brakes so I'm thinking that's why
* I recently dropped and rebuilt the transmission.
* I put a 3 inch body life and 31x10.5 on it, but i have checked and there are not broken grounds, or anything like that, it's my 3rd blazer lift.
* I have access to AllDataDiy if you can direct me to some help that may be there.
* I've all new ball joints and outer tie rod ends on it.

Thanks for any help.

** EDIT **

When it dies and will not restart, there is no fuel pressure in the lines, and it does not build new pressure. I can attempt to release pressure on the release valve and nothing comes out, or it just dribbles.

 

It sounds like your pump is on the way out, but test the relay first.

 

I have replaced the relay, so I know it is not that. The pump that is in it is less than 2 weeks old, could it really be going out that quick? But should the fuel pump connector wires read 5v when not connected to the pump?

 

You should have +12V on the pump main power lead. You should also have good ground to the pump ground circuit.

What brand of pump did you install?

 

I replace the actual pump within the assembly, here is the ebay listing from the pump I bought:

http://cgi.ebay.com/ebaymotors/ws/eB...m=400143273739

Although if I am only getting 5v on the wires running to the pump when I should be getting 12v (note the plug is disconnected from the pump when I put the tester on it), I have a feeling the pump brand is irrelevant to my issue. I know I probably got a junk one, but I needed it fixed pretty quick, and didn't have the $200 to buy a whole new assembly, although I plan on doing so at a later date.

What could be the cause of the low voltage at the harness to the pump?

Thanks for you input so far.

 

Are you sure you are measuring the proper wire? There is a +5V reference wire that goes to the fuel tank pressure sensor.

 

There is a 3 wire plug, and a 4 wire plug, I have been testing against the 3 wire plug, I assume I have been testing against the wrong set of wires. I just know the fuel level gauge stops working when I disconnect the 4 wire, but not when I disconnect the 3-wire. Am I correct in this?

Thanks for your help.

 

The 3-wire plug is for the fuel tank pressure sensor. The 4-wire plug has the fuel level sending unit and the fuel pump in it.

BTW, I made a mistake and typed fuel level sending unit above instead of fuel tank pressure sensor like I was thinking. I corrected it.

 

That explains my voltage irregularities, I will check the voltage on the correct lines tomorrow. Thanks for the input. I'll let you know what I find. Could it be that the fuel pump is failing after it gets warm or something? I'm just curious why it works just fine and then dies, and requires an extended period of time before it works again. Sounds like something is over heating. Could it be that I just bought a junk fuel pump? Would it be worth it to return it (there is a life time warranty on the pump), or should I just look into replacing the entire unit?

Thanks for all your help, I really appreciate it.

 

Aftermarket pumps usually do not last. AC Delco or Delphi are the accepted quality pumps. What is possibly happening is that as the pump warms up, the internal clearances tighten up. While its running, it stays running, but once it shuts down, the startup torque of the motor is not sufficient enough to get the pump moving.

Next time it happens, try this. Smack the bottom of the tank with a rubber mallet or block of wood. See if the pump starts.