Hello all,

This is my first post and I am at my wits end with the truck that I just purchased. I bought a 1989 Ford F150 and it ran fine for a few days. Then it simply failed to start. I put a fuel pressure gage on it and I got no pressure at the rail. I then started to try and trace the problem. When I key on I can barely here the rail fuel pump come on and I get next to know pressure (maybe a 1 or 2 psi). I can't here the in tank pump at all. If I unhook the rail pump I can then here the tank pump cycle on. I hook the rail pump back up and I can only here the rail pump cycle a little. After about thirty minutes of this I hit the key and here the rail pump come to life and I get 40 psi of pressure. The truck starts and runs fine. I turn it off and get the same problem again. I have managed to get the truck started three times. Two times it ran great. One of the times it started and I watched the fuel pressure die right after I started it. In a fit of desperation I started throwing money at the problem. I replaced the fuel pump relay, rail fuel pump, the fuel filter, and the fuel pressure regulator. All to no avail except that now I can usually get about 10 psi when the rail pump cycles and if I keep turning the key on and off the pressure will build to about 20 psi. I can then start the truck and watch the fuel pressure bleed away. Some things that I have found out are that I am getting approximately 12 volts at the relay, 10 - 12 volts at the inertia switch and 10 - 12 volts at the rail pump. I say 10 - 12 because all I have is a analog meter. One other thing that I found is that when I was tracing the fuel lines, the return line is crimped going into the tank and actually has a pin sized hole in it. It must have been this way for quite some time now and I am amazed fuel was ever able to get back to the tank. I don't think that it adversely affected the truck because it still drove fine when I could get the truck running. Any advice would be greatly appreciated as my next resort is to blow the truck in place. Thanks.

 

I assume you don't have dual tanks.
To verify the intank pump is working, disconnect the input line
to the main pump mounted on the driverside frame rail. You pry up
on the plastic clip and the hose will pull off. Catch any fuel in
a drain pain. Turn the key to run and you should see fuel being pumped
by the intank fuel pump. If you don't see any fuel, the intank pump is probably bad. They do fail quite often.

 

Plus , Replace the leaking return line , Having a fuel leak is dangerous .

 

On the left frame rail your truck has a reservoir for the fuel supply. It is located between the tank and your high pressure pump.
I had a friend with an 1986 F-150 that would start running out of fuel
when he got up to about 35-40 mph. He had to replace this reservoir.
In the Ford Factory Shop Manual it shows the reservoir to have a filter in it. It shows that the bottom part unscrews and the filter can be removed. You might take a look at your reservoir. Hope this might help.

 

Thanks for the tips. Tommorow I will try and repair the leaking fuel line and then I will check the fuel reservoir and probably go out and pick up an in tank fuel pump. I figure "why not", since I have replaced almost everything else. The most logical place to check would be the in tank fuel pump but I just can't get why the rear pump would cycle when I unplug the front pump and the rear pump will not cycle when I plug in the front pump? Thanks for the help and I will let you know how it goes.

 

my 89' f-150 had rusted out gas tanks and this same problem occured with me....the rust would clog up the lines and as it sat for a while the rust would some how clear out and as soon as i turned the key on it would pump it back in...had to get both tanks and intank pumps replaced...