I have a 1994 Ford F-150 XLT 4.9L, it has the dual tanks. I just replaced the front fuel pump a few months ago, because the rear tank started leaking and the fuel pump in the front had failed a while back. Everything had been working great until the other night, I was out driving when the headlights started to dim and then the truck died. I tried starting it back up to realize that the fuel pumps weren't kicking on anymore. So after a while I thought the Fuel Pump Inertia Switch may have been triggered but after removing the kick panel I found it was completely intact. So I went to the Power Distribution Box and found that Fuse 16 - Fuel Pump Feed had blown. So I took another fuse from an unneeded place and put it in, turned the key to ON and I heard the fuel pump buzz away. She fired right up, then after about 3 seconds she died again. I looked again and the fuel pump fuse had blown again. I put a 40 AMP fuse in the slot and barely made it home using the rear tank. I replaced the Fuel Pump Relay and got proper fuses, now the Front Tank's FDM doesn't even whine and won't start at all, whereas the Rear Tank's FDM whines and starts. I've looked into it and found that the Fuel Pump could have a short in the wire, or a pinched wire. Where would I have to look? Is this an issue that replacing the FDM would solve? What am I looking for in the wires? Any help would be greatly appreciated as this is my only vehicle.

 

You obviously have a short somewhere, you need to track it down. Don't run the truck like that, with that fuse, you risk either burning the fuel pump or starting a fire in the wiring harness. I'm sorry I can't be of any more help, others will surely chime in and help.

 

I think I may have burned the pump because it doesn't whine anymore? How can I track down the short? What am I looking for? And can this be fixed?


Thank you for your time,
TheKhaos

 

Sounds like the electric pump in the FDM started to lock up as you were driving. I would imagine if you had a short that didn't blow the fuse immediately, that it would be an intermittent short.

When you ran out of fuses and had to use a 40A to get home it either burnt up a connector, some wiring, the motor, or the pump just finally locked up for good.

Make sure the fuse is good and that the front tank is selected, then disconnect the wiring at the FDM and check for power. If your meter leads ain't long enough to reach the FDM harness from the cab you'll have to have someone turn the key for you while you watch.

If you have power, it's fairly safe to say the FDM is dead. But if you really wanted to and if you have an inductive ammeter, you could reconnect the wires to the FDM and power it up again while watching current draw. This would verify that it was the source of the problem.

 

Well I appreciate all of the information, I have yet to run a power test on the FDM. I just recently had a daypff so i went ahead and dropped the tank and replaced the FDM. It started and blew the 20AMP again so I put a 30 in and it hasn't died yet. But I am experiencing some very weird problems. On occasion it willtry to die at idle but never does. If I accelerate too much it will bog down amd try to die. When I'm at a red light and it turns green just about every time I can't get back up to speed because it instantly starts bogging down so I have to switch to the rear pump and it works perfectly fine and once I get it back up to speed I can switch back to the Front tank. But then eventually even at a steady speed it will randomly start bogging down once again. Any ideas?

 

I'd say put a fuel pressure gauge on it where you can see it from the cab. Watch the pressure when it starts to bog down. Then try it while running the other pump. Then you'll know for certain it's a fueling problem and not something else that just so happened to show up at the same time.

 

What exactly is the process of checking fuel pressure? I pulled codes, one that sticks out is Code 543 "Fuel Pump Secondary Circuit Failure: Battery to PCM"