Does the HP fuel pump on a 1988 F150 5.0L have a check valve?

I'm sure that there is. Sounds like yours isn't working. A vapor lock isn't likely.

Check fuel pressure regulator,may be bad.

Regulator fine. No smoke. Engine runs like a top (125,000 actual miles) accept hard to start after a short stop.

No way to check that. I am aware of the check valves on the pumps in the tanks. Since both tanks act the same way, I suspect there is a checkvalve in the HP pump. I seem to recall reading that somewhere.

I have replaced the regulator. I will replace the HP pump next week.

A retired Ford mechanic told me that Ford tried to make the dual tank system work with several different schemes, but never was truly successful. My dad had a 69 3/4 ton Ford that had 2 tanks. The switching mechanism consisted of a manual valve on the floor left of drivers seat, and toggle switch on the dash to switch sending units. This system worked, but you had to remember to throw both the valve and the switch. Ford finally gave up and went to one tank- but larger capacity. Duh!!!!! And they got rid of the tire wrecking Twin I Beam too. Duh!!!!!! I got a recall notice on my 2012 Taurus today. It seems the license plate light cover can be affected by road salt, and cause a fire. Things never change.

And, I had a 92 F150 with the same darn transfer fuel from tank to tank issue. Ford installed check valves in the fuel lines. Seemed to cure it.

Had the HP fuel pump replaced today. It seems to have fixed the problem. Now the water pump went out!!!!!!!

OUCH! It never rains, it pours.

These things come in threes.

I just replaced a fuel pump in the front tank of mine and now im getting no fuel out of the lines

Its vapor locking when temps get over 90 the 88 f150 will vapor lock .has yours still have the injection fan on it .when I took mine off a few years back mine vapor locks every summer I changed all the pumps and everything else trying to fix it more then one time I rigged me a new fan on mine I'll be testing it this week