2000 Grand Flex, normally burning E85. Fuel pump runs, but no output. Jammed the fuel pump relay with a toothpick and pump runs continuously, but nothing comes out. Maybe occasional spurts. Fuel level is low, but I've had it lower before without running out; also added 2 gallons of regular 87. Sometimes the car starts and runs, but usually not. When it works, the injector rail pressure measures 50PSI (0.39MPa). Inside the pump assembly is a pressure regulator stamped "0.35MPa". Compares favorably with measured value 0.39MPa.

Took apart the pump module. Could someone explain the function of the module, seems over-complicated.

There is a large filter sock on the module, but this is not the intake! The intake is a simple one-inch screen on the bottom of the housing, with a one-way flap valve. The pump itself draws from a sump at the bottom of the housing.

The weird thing is, the output of the pump goes through a plastic device with two outlets. One has a rubber-ball check valve that feeds out of the tank to the fuel filter. The other is an open port that feeds back into the tank through the filter sock! I don't understand this device, the pump has its own internal check valve. The plastic thing seems designed to feed the output of the pump right back into the tank. There does not seem to be any valve or restriction in this pathway except a straight channel about 2mm dia. and 1cm long.

My best guess is that the pump is supposed to produce so much volume that the outlet pressure still exceeds 50PSI even though a large portion is shunted back into the tank. In other words, the flow rate through the 2mm channel is so high that the pressure drop exceeds 50PSI. The purpose of the shunt would be to clean the fuel in the tank by cycling it through the sock (?).

I have tested all the check valves by mouth, both sucking and blowing, and they all seem fine (the intake flap, the fuel pump, and the plastic check valve). Both the intake screen and the sock are completely free-flowing. So why doesn't anything come out?

My next move -- if it stops raining in SE Wisconsin -- is to remove the tank completely so I can verify that the fuel level is high enough (why wouldn't it be, it always was before), and test it with the pump back in the tank.

BTW -- if you like testing your fuel system by mouth, you really should try E85. It tastes a lot better than Regular.

 

Did you ever figure this problem out? Mine's doing the same thing.

 

Did you forget to prime the pump before dropping it in the tank? It needs about 2" of fuel sloshing around inside the plastic housing or it won't work.

Ask me how i know.

 

Thanks for the tip. I did not do that, but I did get it working. Now my question is what if you run the tank dry my mistake? How do you prime it?

 

The pump shouldn't need to be primed, I never have and have never had an issue.

 

To prime mine, I just poured some gas down the small opening on top of the housing. Originally, when I installed the new FP, there was no fuel getting into the plastic housing when I pulled it back out. The pump I removed did have a couple of inches of gas inside and that pump worked fine. Reason I replaced it was to fix the fuel level sending unit that was not working.

I imagine running the tank dry might burn out the FP, depending on how long you ran it that way.