Fuel Pump

**da pope** · 08-09-2009, 09:05 AM

Tried to start my Burb today and it will not crank. It sounds as though it is trying to start, but no sound from the fuel pump. Checked fuses, none are blown. The relay rattles when shaken. My fuel pump is loud and you can here it when you turn the switch to the on position. There is no sound now. Is there another fuse box besides the driver door and driver side engine? How are the fuel pump fuses labeled, we may be missing something? Or, is it truly the pump? Any help!!!!! Driving Jeep and not happy!!!!

**Z07** · 08-09-2009, 09:16 AM

The fuel pump is powered via two parallel circuits. One is from the computer through the FP relay. This is powered when the key is set to run and again when the comp detects engine start. The comp will keep power to the FP through the relay until engine shut off. The other circuit is through the oil pressure sending switch. This will power the FP once it detects oil pressure greater than 4PSI. Typically if a FP relay fails the engine will still start if you crank it long enough for the starter to turn the motor and therfore the oil pump to produce that 4 PSI min.

As a test you can look for other relays on your burb that are the exact same as the FP relay but for non-critical systems like AC or horn etc. and swap them. You can also disconnect the oil pressure sending switch from the wire harness and jumper the harness connector. This will power the FP from the time the key is turned to on until it is turned to off.

There is a persistant myth out there that the fuel pump will be turned off if the oil pressure drops. There never was any truth to this myth what-so-ever.

If you do replace the pump be sure to replace the sock too. The best thing you can do to promote FP longevity is never run less than 1/4 tank of gas. The pump is cooled by the gas that covers it.

**2COR517** · 08-09-2009, 10:22 PM

Does the truck run on ether? Although it certainly sounds like your pump is not working, could be ignition. Ether would rule that out. Also, give the bottom of the tank a good whack with a mallet or hammer, right in the middle. That might get the pump to start.

**tattooed4life** · 08-09-2009, 10:48 PM

Sounds like all the rest.............dead pump blues. I had my gf cycle the key on mine while I had my ear against the tank just to verify there was no pump noise. I also did all of the prelim tests before I pulled my tank. In the end it was no pump sound and I was dead in the water.