scorpion7667

I have a 88 F150 4.9L The truck runs great except for the fuel cuts out , and stalls a little at random. (it doesn't die just sputters a little) I know that when this happens the HP pump isn't getting enough fuel, but why? I have replaced the Hi-pressure pump, and the low pressure pump-sending unit as one. I have tested power to the pumps, and ran a computer diagnostics on it, no problems. I can hear the pump running then it gets quiet when it stalls out, but if I wait a second it starts humming again and all is well. I think there could be a possibility the ECM is bad, but wanted to get some opinions first before going ahead with that. Also I have replaced the relays and the pressure regulator, and done a visual inspection on the wiring and connectors. I am now stumped with this problem. I was thinking about running a set of wires down to the pumps from the battery with a toggle switch to see if that would stop the problem. Thanks in advance.

Butchart

See my earlier post, I had problem with my fuel pumps not shutting down after turning the ignition off. Found out the problem was the fuel pump relay that is mounted on top of the drivers side inner fender. I had trouble pulling away from stop signs and lights. But sure is good now, and I believe the relay was causing a resistance to the fuel pumps and a low voltage would not bring up enough pressure for the injectors.
However, you didn't mention cleaning out or replacing your fuel filters. On my 88 F-150 there is the stainless steel one mounted on the frame, but further back there is another fuel sediment bowl which your line runs through, so check them out. You even could have got a new faulty fuel pump relay too.

scorpion7667

I read through just about every post, and I did read yours also. It made me think about the relays again, but I don't see any problems there at all. Sorry I forgot to mention that I did replace the fuel filter, and cleaned out the sediment sump, and replaced the rubber o-ring. I also replaced the relays, and tested voltage to them. It is real hard for me to test the voltage when it happens, because it comes and goes at will. I was told by someone else the other day that it could be the ECM, and that is kinda what I was thinking. Thanks for your help. I think I will check out the wiring and those relays one more time just to be sure. If you think of anything else it would be a great help.

Butchart

You might also want to check the inertia switch under the dash on the firewall drivers side, it could be playing tricks on you, make sure the button is in the down position. Up position cuts off the fuel, haven't heard of anyone having trouble with them, but you never know. I'm okay on the general electrical stuff, but not the computerized junk thats on our vehicles today.