Bad censor????

I have a 87 cherokee and im having problems starting it. You turn the key on and wait for the fuel pump to run and then start it. well it usually starts but some times it does'nt. If you try to start it before letting the fuel pump run it will never start. You can eventually start it if you keep turning the motor ove and try and pump it for about 5 minutes. could it be the tps sensor or something else.
thanks.

Replace the crank shaft sensor.

Could be the check valve for the fuel pump.

I believe the 87 had an external fuel pump which makes it easier to change.