This is my grandson’s truck. It’s been running well for the last year and a half, since you guys helped with an intermittent/poor running problem. Thanks again for all those that helped me out with that problem

It's an 88 F-150 with a 5.0 liter V-8 with two gas tanks. The truck will start OK, but will not continue to run. It seems to be starving for enough gas to keep it running. They connected the code reader and got no error codes. Based on that info I suspect something in the Fuel delivery system.

I have the electrical diagram labeled "1988 F-Series Fuel Tank Selector". It shows all the electrical components including the fuel pump relay, inertia switch, EEC relay, and fuel tank selector switch. It also shows a front tank sender unit & pump, and rear tank sender unit & pump. Then it shows an external high pressure pump, Are there really three fuel pumps?

I also have a diagram labeled "Type 2--Dual Tank, Dual Fuel Delivery Module". It is a simple diagram showing the fuel flow from the two tanks through the filter, pressure test point, injector, and pressure regulator, then returning to the tanks.
I understand that the returned gas is diverted to the proper tank based on the check valve that is part of the in-tank pump/sending unit.
I would like to find a diagram that shows the location of the various components, so I will have a better idea how to troubleshoot the components.

I would appreciate if someone could direct me to such a diagram and also tell me if the two diagrams are the correct ones. Also any suggestions as to where to begin the troubleshooting would be very helpful.
Thanks, Les


PS: I can post the diagrams if necessary.

 

That 1988 F150 has 3 fuel pumps and a dual function reservoir. The in tank pumps are low pressure. The frame mounted pump is high pressure. A complex system.

 

Your 1988 Fuel system:
Attachment 280309





Selector valve, Yours may not have the filter in it:


Low Pressure boost pump:


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Sounds like the frame mounted reservoir is faulty, not the tank pump. The reservoir is not electrically switched, but driven by pressure from whichever tank's pump is running. That happened to my '88 F250 302. I got a new Ford reservoir from Amazon couple years back, reasonable price.

 

I found the this reservoir on Amazon. F1uz9b263b Reservoir Assembly - Fuel selector valve OEM Ford for $180. But when I searched elsewhere by that part number, It says 1989+. Is that the right one?
Or is it this one, Standard Motor Products FV5T which is only listed as a Fuel Tank selector valve for $59?

Thanks for any replies, Les

 

Good info, but check your fuel pressure before you replace anything. Should be around 32 lb at idle, will jump to around 40lb with the vacuum line to the fuel pressure regulator removed.

There is a very useful test point at the diagnostic connector for the fuel pump. If you ground this point with the key on, the relay will pick and the pumps will run continuously. The ECU shuts down the fuel pumps if the engine is not running, which can make diagnosis difficult. I used the test point for a "get home" workaround with one truck I had. For electrical reasons, the EFI system was not allowing the fuel pumps to run, although I could start and run the truck with the fuel pump test point grounded. This is a safety system and I would not recommend bypassing it for any reason other than testing.

Does the problem happen with both tanks? If the problem is with one tank, check the in tank lift pump for that tank.

FWIW, the frame mounted inline pump and the multi purpose reservoir are quite reliable. Personally, I have never had one fail.