My truck's been in storage for 3 years,ran fine before but now it runs like fuel supply is cut off.
I did notice when I replaced filter that no fuel came through and I pulled gas cap in case closing system kept fuel from traveling.
Is there a way to test to see if strainer in tank is clogged?

Engine starts but backfires,stalls and dies when gas pedal is pressed.

 

Reads like more a pump issue than screen.
Engine would idle fine and drive but would start stalling out as screen limited full flow, i.e. it would act like a dirty fuel filter, because that is what it is :)
Yours reads more like a pressure problem.

Fuel Pump(s) should come on for 2 seconds, when key is turned from off to run, that's standard Ford(and everyone else) fuel injection priming done by the computer.

The 1987 Ranger should have two fuel pumps, low pressure pump in the tank from the old carburetor days and a high pressure pump in the frame rail(by the fuel filter) added to get the 30psi of pressure needed for fuel injection.

There should be a Factory splice located near the high pressure pump where they got power from the 12v line that runs to the low pressure pump in the tank.
Line only has 12v when computer turns on pumps.
This splice is known to fail, so worth a look.

I would check if both pumps are coming on when key is turned on, maybe feel the tank and then the frame rail pump while some else turns the key, you can cycle the key off and on as much as you want, won't hurt anything.

On the fuel rail(for injectors) there is an FPR(fuel pressure regulator), it is hooked to the return fuel line, it will have a vacuum line attached, inside FPR there is a rubber diaphragm that can crack and leak fuel into the vacuum line where it is sucked into the engine, FPR also has a spring inside that holds it closed so system can build up pressure.
Remove that vacuum line and smell it for fuel.
If no fuel, suck on that vacuum line(attached to FPR) and make sure it holds vacuum.
Replace FPR if fuel is found or it can't hold vacuum.

Also on the fuel rail is a schrader valve, looks like a tire air valve and works the same way.
It is for hooking up a pressure gauge to test fuel pressure.
Cycle the key on and off a few times, assuming you have checked that the pumps are coming on, and then carefully push the center pin on the schrader valve to see if there is pressure in the fuel rail, it can spray 30ft, keep that in mind :), so best to test on cold engine with no cigarette in your mouth.
If there is little pressure then the FPR could be stuck open.


As for the original question:
Find your OBDI(EEC) port in the engine compartment, passenger side firewall, FP(#6) port is to turn on fuel pumps manually, GND(#2) is the jumper connection.
Lay out is:
.....#1 #2
#3 #4 #5 #6
So you use a small wire(jumper) to connect #6 contact to #2 contact and that will turn on fuel pumps manually.
This activates the Fuel pump relay, you are not supplying 12v thru the jumper, it is just a ground which activates the relay, that is how the computer controls the fuel pumps.

Remove fuel line at high pressure pump, the one going to the tank, place container under fuel line, turn on key, connect jumper wire, run fuel pump for 30 seconds, only the low pressure in tank pump(with the screen) should be filling the container.
In 30 seconds you should get about a pint of gas in the container
You could try not using the jumper and turning key on 15 times(2 seconds of power) to see if you get a pint, but never tried that method