i have a 1966 ford f-850 fire truck with a 401 c.i. engine. the in-tank electric fuel pump has gone bad. it is an after market pump in a tank put on by the fire truck manufacturer not ford. i've taken it to a few auto parts stores and no one has seen anything like it so finding an original replacement is looking impossible. what i need to know is if i purchase an inline fuel pump what psi should i go with? any help is greatly appreciated.
Sometimes fire trucks used a return to tank system similar to modern fuel injection to combat vapor lock when pumping stationary for a long period. So the in-tank electric pump may be more of a constant displacement type than a carburetor pressure limited type. What you will have in this case is a pressure fuel line running to the engine, and some sort of bypass valve at or near the carburetor, and then a return line to the tank. In this case you will need a different style of pump.
A caution here. The aftermarket pumps I see in catalogs worry me a bit because they usually specify something about racing applications and I suspect that they might not have the longevity or reliablilty required for an application such as this. There is one company I know of called Facet that makes commercial duty fuel pumps. I think Holley also makes some but they may or may not be good enough for the application.
The Ford fuel pressure specification for the 1966 401--irregardless of whether it is a 2V or 4V engine--is given as 4.5-6.5 PSI.
Was your electric fuel pump activated by a primer switch on the instrument panel? If so, it should be an auto pulse electric unit. They were used on Ford fire apparatus built by both Autolite and AC Delco.
After being involved with Fords and repair parts for over 30 years, I most surely agree with Hotwrech's post: I have YET to see a SINGLE Fawcett electric fuel pump that was worth installing!