1985 Ford Ranger 4x4 2.8 v6 w/mechanical fuel pump
Fuel pump will not fill the carb bowl after the truck sets for a time. After manually filling the bowl, truck starts and runs fine. Actions taken: replaced mech fuel pump; rebuilt carburetor; removed gas tank for inspection - all OK there; fuel lines looks good. With truck running, fuel pressure at carb is 7 psi. I assume the rod that actuates the full pump runs off a cam lobe (?). If so, could the cam lobe be worn such that the pump diaphragm does not get a full stroke?

 

Mechanical pump needs RPM above 400 to actually start pumping very well
You can disable spark and remove fuel line from carb
Put a container under fuel line then crank engine to see if it can pump at lower RPM, it should pump a little fuel.

Question, to me, would be why would float bowl be empty, it would have to sit for many many months to evaporate unless there is a leak.

7psi would indicate pump is working fine to me

Mechanical pumps work on siphon pressure from tank to keep fuel in the line from tank to pump
If that fuel line doesn't have some pressure then pump is trying to pump air, which it can not do.

In the old days after running out of gas, lol, I remembered putting a hose in the tank, gas cap off, then blowing in it to get the siphon started because mechanical pumps just can't "pull" gas from the tank.

Push rod should come out, although not sure on the 2.8l, and you can check the end for abnormal wear, but never really heard of that type of problem in mechanical fuel pumps

 

Thanks for reply RonD.

I disconnected the fuel line at carb and routed to a container. Disconnected the inlet line to the fuel pump and dropped it down to a container of gas right below the fuel pump. Cranked on the engine for 30 seconds - not a drop of gas came out of the fuel line.

Removed the fuel pump. Checked the fuel pump rod movement. The rod moves about 0.1875 inches. I wish I knew what the spec was on the rod movement. Pushed down on the fuel pump internal lever - it only moves about a quarter of an inch.

I am ordering a another new fuel pump.

 

Mechanical fuel pumps can't "draw" fuel up into them, they need to be gravity fed.
i.e. they can not pump air, seals are not that tight.

repeat test but put container higher than pump inlet and siphon to prime it
so pump inlet has fuel inside, then I bet it will pump

That being said the .18 movement seems too little, .3 to .5 would be expected 3/8" to 1/2" travel on push rod
But that really depends on where the push rod is on the fuel pump lever, if it is close to pump then less movement is needed.
I am used to the chevy pumps that had the longer levers so needed the longer throws

Just looked up the 2.8l pump and it is direct drive so .18 may be fine
The push rods are made of a softer metal than the cam it rides on so rod would show wear if oil flow was poor, cam would still be fine

These pumps are rated at 20gallons an hour, but at 3,000rpm, so it won't pump too fast just cranking it.