Hi, I'm new at this. Just found your site today while researching my problem. Maybe someone has an idea. I have a '90 F150 with an EFI 4.9l., 5 sp manual. Dual fuel tanks with FDM pumps.
One day it will start and run just fine, next day it will turn over but not run. I have replaced the fuel pump relay,eec relay, coil, hall effect sensor, rotor button,dist cap,plug wires,ignition control module,and fuel filter.
I took it to my local garage. They could not find anything wrong. They said I have good fuel pressure. They checked the computer(no codes showing). Good spark. They agree I have a problem, but,they dont know what it is. Any suggestions?

 

I replaced the connector at the top of the tank itself. $3.50 and my fuel pumps always work now. They would just loose connection sometimes.

 

Thanks. I dont have bad connection at the tank. When I turn the key I can hear the pump running. When I switch tanks the other pump turns on. Normally the pump only runs for a few seconds with the key on without cranking the engine. When I have the no start\run problem the fuel pump will not shut off. It will keep humming until I turn off the key.

 

The pump running and not shutting off sounds like its not pumping up to pressure or picking up fuel to pump. Clogged strainer maybe or the pump itself. That will be hard to check without pulling the pump from the tank. The clogged strainer happened on a buddies chevey blazer, miserable job just to get to a $3 part.

 

It only takes 4 things for an engine to run; fuel, air, compression, and ignition. next time it doesn't start, one of those must be missing. If you can identify which one, it will be much easier to diagnose.

Okay, that being said, I think it's your ignition switch.



Take care,
~Chris

 

Thanks for the suggestions. I'll get this thing figured out eventually.

 

If the fuel pump just keeps on running, and it should not matter which tank your on, then it is your ECU relay. Not the fuel pump relay but the other one. If you look at both the relays, they look the same as far as the 5 posts insides. One has a lip on the side for the ECU. The fuel pump relay is the samething minus that outer edge. What I did was since I had another fuel relay, I just clipped off that edge and plugged it right in. Turned the key, pump came on, got up to pressure, and truck started! Haven't had another problem.

 

Is the ECU relay the same as an EEC relay? I changed both the fuel pump and the EEC relay. I will try an ignition switch this weekend.

 

I have much the same problem, good spark at the right time, correct fule pressure, no trouble codes, and the darn thing will not start. I'm stumped.