New pump, no fuel pressure at fuel rail??

Question edited for clarity. Cranking IS turning over. You are cranking but not firing, or starting, or running.

If you haven't much pressure at the rail, your likely problem is not enough fuel pressure and the fuel pump needs replacing. One post here says you need 39 PSI and another says 49 PSI. What do you have? You need to test with a pressure gauge.

https://www.google.com/search?q=1994+jeep+grand+cherokee+laredo+4.0+fuel+pressure+specs

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If the fuel pump(s) run while the pressure is falling, replace the fuel pressure regulator and (although I'm sure you've already done this), replace the fuel filter. If the fuel pumps appear to be turning off by themselves, replace the inertia (fuel cutoff) switch.

The computer might have to be reset.Check you manual to see if you can reset it or try disconnecting the battery.

Check for a feed wire from the battery that is bad. Fuseable links. Feed the fuse box directly from the battery to see if it will start.

If the pump starts to jam it wills seem like it won't run. The stuttering on startup is also related to a failing fuel pump as the intank pumps in our Jeep (I have the same ZJ)

Next time it won't start, try hitting the fuel tank with a small hammer (lighty as per not to crack it)
This can sometimes jar the pump in such a way to get the fins spinning again. If this works I would reccomend replacing the fuel pump.

You should also hear the pump prime when you turn the ignition to on (before start)
Priming the pump 3-4 times can help the stuttering on startup.

You can also get a fuel line pressure tester from most auto parts stores and verify that you are holding pressure after the pump is off.

Cheers
Dave

there is no fuel pump cut off switch . put a fuel pressure gauge on the fuel rail schrader valve turn key on you should have 40+ pounds of pressure if you dont the pump is not working open the relay center under the hood swap the fuel pump relay with the wiper relay and try again if no pressure its not the relay its the fuel pump if you do have fuel pressure that means the relay was bad get a new one the car should start if you do have pressure and the car wont start the injector circuit is dead and what causes this is the crank sensor located on top of transmission bellhousing on driver side auto parts store 38.00 dealer 170.00 when you change it make sure to push it in and hold it while you tighten the bolt hope this helps and please dont forget to rate my solution

#1 NEED TO VERIFY SPARK AT SPARK PLUGS # 2 CK FUEL PRESSURE AT SCHRADER VALVE ON FUEL RAIL ,,PRESSURE DEPENDS ON TYPE ENGINE ....IF NO SPARK AT SPARK PLUGS CHECK SPARK FROM COIL WIRE , IF NO SPARK AT COIL ,CHECK VOLTAGE TO IGNITION COIL SHOULD BE 12 VOLTS, IF NO VOLTAGE AT COIL ( KEY ON ) CHECK FUSES THEN IGHITION SWITCH. IF NO FUEL PRESSURE AND FUEL PUMP RUNS REPLACE PUMP .. CK VOLTAGE TO FUEL PUMP WHILE CRANKING . CK USING PUMP GROUND WIRE AT THE PUMP CONNECTOR THIS WILL PROVE GROUND ALSO. USE TEST LIGHT TO VERIFY

sounds alot the the pcm it controls the fuel pump and ign system but the anti theft would keep it from starting because the key has a transponder in it programmed for that vehicle and that would kill all ign if triggered

The fuel pressure should hold at or near the 45 lbs after you shut the truck off.
You have one of three problems causing this.
One, the fuel pressure regulator is leaking internally and allowing fuel to return to the tank via the return line. To verify, use a pair of pliers and gently pinch the return line off. Turn the key on to the run position, the pump will run for 2 to 5 seconds and pressurize the line. Watch the pressure gauge, it should hold pressure. If it does, change the regulator.

Two, the check valve at the pump is weak. To verify, turn the key to the run position, when peak pressure is reached, gently pinch the pressure line and watch the pressure gauge. If the pressure remains near the peak pressure the check valve is bad. Replace the fuel pump.

Three, if neither of the above procedures work, you have a leaking injector. You will want to remove the fuel rail, pressurize it to find the bad injector.

Any one of these failures will cause the "vapor" issue you describe.

Good luck, let me know what you find.
Regards,

Does the vehicle crank for extended period of time upon first starting? If so the fuel pump needs replacing.