water pump run but no water

[ajriding]

I have a Shurflo 2088-404-144 pump running but no water coming. I have looked at forums, but not finding answers.
My pump, when working right, will make an almost grinding noise (good) when it is bringing the water system up to pressure. Now, that it is not working, I can barley hear it running. There is some gargling sound too, so maybe water is being agitated at least.
My water tank is next to the pump, and there is a 5 inch line going to the pump. There is no leak between the tank and the pump.
I took the pump apart. Nothing looks broken or out of place.
I put some water into the pump before attaching the water lines. It has never needed this, but worth a shot.
My efforts did not help.
The motor runs without the pump attached to it on my bench. It probably would turn 800-2,000 rpm or so. Fast, but not super fast.
Either the motor is too slow, or some parts are bad. I can get replacement parts for the pump, but do not know what would go wrong. I cannot see anything broken or otherwise obviously bad. It has sat for a year dry.
What could I do to fix?
Would a bad pressure switch cause water to not flow even though the electric motor is running?

[ajriding]

SOLVED
I ran the pump with the outlet pipe disconnected and while I pondered that there can not possibly be anything wrong for several minutes water finally started flowing.
Still do not know what the issue was as this has never happened before.
What I learned:
These diaphragm pumps should last a very long time.
The only moving part is the electric motor.
Keep debris out (though not my issue this time).
The pressure switch, if it goes bad, will cut power and make the pump not work.

[MWJones]

Bench test it with a length of hose connected to the in side of the pump and into a container of water. If don't pump water - bad pump.

[ajriding]

Water heater is full. I also tried running the pump with water pressure coming in from a water hose.
Faucet was tried open and closed (when system is dry after winter the pump will usually push a great deal of air pressure through the lines before water flows).
I found once piece of plastic debris, but that did not fix the problem. I just washed it out and found nothing.
I don't have a water fill valve, not sure what that is. My water tank gravity feeds the water pump when full, the pump is next to the tank, so sucks it when low.
I put diaphragm on without the rest of the pump head, ran it on the bench and it sounded very similar to the good sound, so I assume the motor is running at the right rpm.
I will try running it disconnected from the outflow.
thanks for the responses.

[midnightsadie]

my pump has a valve next to it for sucking in rv antifreeze ,IF that valve is in the wrong position? it will not suck from tank.

[enblethen]

Do you have a water fill valve? Is it in the operate mode?

[Almot]

I asked had a similar problem - motor running but no water. In my case, the sound was same as usual. Turned out to be debris in the pump.

Check the output hose- disconnect it from pump, put some pan under and see if it throws any water out.

[Old-Biscuit]

Do you have a faucet open with pump running?

Is water heater full yet?

Bad pressure switch will make pump run continuously or not at all but has nothing to do with no water flowing.

Air leak on suction side of pump will not allow pump to prime.