I've got a 300 straight 6 in a 1988 F-150. I am having a problem with the truck acting like it's out of gas when it's not. The fuel pump on the frame rail hums like it does when fuel is low and then it stalls. When I turn the key to prime the pump shortl after stalling, it makes a loud noise as if air is passing through it. I have replaced the in tank fuel pump, the fuel pump on the frame rail and the fuel pressure regulator. What could be the cause? The vehicle was always reliable and never left me stranded in 4 years of owning until this happened.

 

This is a EFI system right? I should tell you I am not up on this new fangled EFI stuff!


Why did you replace the low psi tank pump, the high psi pump on the frame rail and the regulator? Was it to try and fix this issue?
I did not see it posted about changing out the fuel filter?


Do you have a fuel PSI gauge you can use to see what fuel PSI you are getting OR not getting? With out one it is a crap shoot not know what is going on.


But lets try something using a test tight. You are going to need to jump out some safety switches I hear the EFI systems have.


This is where it gets ify 1 I hear is a oil psi switch were if the motor is not running (no oil psi) the switch will not close sending power to the next switch.
Next switch and I forget the name but should be closed all the time to let power go thru till you get in an accident or hit and them opens. This way if the motor is still running the pump will stop. I seen posted it is on the firewall behind the glove box.
The last is the fuel pump relay to make sure it has not failed open.


I would say jump them all out FOR TESTING ONLY! and with the fuel PSI gauge see if you get pressure if not then you need to do more testing.
I would check for power at each pump and if you do have power then you need to test each pump.


I would start at the low psi tank pump and see if it is pulling fuel up out of the tank. I do not know what the spec is on how much fuel it should pump in what time or what psi but I would think it would have to be pretty good to supply fuel to the high psi pump.


If the low pump is good do the same with the high psi pump but I think just a PSI test at the pump would be good enough? Then test for psi farther up the fuel line.
That should get you started on things to check.
Dave ----

 

I should also say may want to post this over in the 80-86 truck area.
Yes I know you have an 88 but it is pretty close and the guys over there know the EFI system better than I do.
That is where I got most of that information from, just ask for help we don't mind.
Dave ----

 

If you haven't pulled the diagnostic codes, do so. They might point you in the direction to go.

 

Dave, fuel filter was also replaced, I forgot to put that in the description. I replaced the parts listed hoping to resolve the issue. The frame rail fuel pump was the first thing replaced because due to the humming noise and seeing how rusted/corroded it was, I thought it was going bad. The switch you mention is called an inertia switch, its working as it should. I don't have a PSI tester. And to Harte's reply, I have no codes.

 

Well if it is not showing codes and is running badly I would pick up a fuel PSI gauge to test what is going on with the fuel system. If the fuel system psi is good then we need to look else were.


The gauge is not a lot of money and is a nice tool to have down the road.
Dave ----

 

Check your computer for bad capacitors. I had similar problems in my 1993 I6 and replace the caps and fixed a corroded track (after replaced the fuel pump too). The case on the computer will come off. Look for leaking black / brown substance under the caps or the top will have a rounded top instead of being flat. Look for green corrosion the copper tracks, gently scrap to see if they are broken.

Soldering iron, insulated jumper wire and some video & modem computer boards is what it took to fix mine.

Re manufactured computers are $70 - 100 bucks online.

 

Byron: Are you talking about the computer on the river side near the washer/coolant reservoir or the cluster of wires in the wheel well of the driver side?

 

Dave: How do I test the fuel pressure? I've never done so before.

 

Sorry getting back so late.
The gauge should come with fittings to fit different ports.
I don't know the EFI systems but there has to be a test port for checking psi.
If it has a fuel rail ckeck it for a port. Could also follow the injectors and fuel lines to see if you can find a port.
Dave - - - -

 

Is it possible that it could be vapor lock? After doing additional research based off the symptoms, I am led to believe that the after a bit of driving, the fuel begins to boil when the engine is warm, causing air to go through the pump. Could that be causing all this trouble?

 

Sorry for the delay. Since mine is a 93 and yours 88 things will not be in the same location. Mine is located below the master cylinder to the right through the firewall. I had to unscrew a bolt from the connector in the engine bay and remove the computer from under the dash.

 

Being you have a (stock?) pump on the frame rail and guessing a pump in the tank(s) this is EFI as I did not see this posted.


Because the fuel is being pushed from tank(s) to motor and is under PSI this keeps the fuel from boiling/vapor lock.


You really need to pull codes and check fuel PSI both cold and when warm and happens.
Dave ----