Engine shut off while driving will not start

Does the fuel pump even run for a few seconds after you first turn the key to run?
If not, check the fuel pump fuse and if okay, try a new fuel pump relay or swap one it.

Fuel pump does not kick on. Swapped relay, and fuse is good.

Okay, does the fuel pump relay even click when you first turn the key to run, before you turn the key to start?
If you cannot reach the relay and put your finger tips on it to feel, then have someone else turn the key while you feel if the relay clicks.
If not, make sure any check engine lights or security lights go out after fifteen seconds or so and not stay on or flash.
If a security light stays on or flashes, try a spare key or clean that key where the pellet is and try again.
Check the fuses for the PCM as well.

Fuel pump relay does not click. PCM fuse oayk. PCM relay seems to be clicking as well. Are we looking at crankshaft position sensor, or camshaft position sensor next? My wife did experience a similar situation a week ago, but was able to restart. Or, are we up to a bad computer already?

That would be a no for both the crankshaft position sensor and the camshaft position sensor.
The fuel pump should run for two seconds when you first turn the key to run, before having to crank the engine over. Them sensors have nothing to do with it, because the engine is not cranking over.
The fuel pump relay is fed from a fuse #12 behind left side of dash, with the key on run/start as well as a fuse #24 in the PDC under the hood, that is hot all the time.
Although since the relay does not click I am concerned with that fuse #12 left side of dash.
Can I assume the pcm relay you are referring to is the asd relay? If so, then that fuse must have power going through it cause I was just going to ask you to test both sides of that fuse on both sides with the key on run.
That fuel pump relay is grounded by the PCM. A brown wire at pin #19. You could use a twelve volt test light and ground that brown wire, turn the key to run and listen if the fuel pump runs now for two seconds. If so, the problem is with the PCM , its powers/grounds. The are usually more than just one power and ground for the PCM , so check them all.
Also, just because that ASD relay clicks does not mean it is supplying power to the coils, injectors, and the PCM when the key is on run/start. If not, check them ASD relay fuses, the #6 in the PDC and the fuses after that ASD relay, #16 and #26 also in that PDC.

By pin#19, you are referring to location on the PCM itself? Is this marked on the PCM ?

I have another Cherokee that I have swapped relays from for testing purposes.

Yes, pin #19 on the PCM connector, look for a brown wire.
That probably just means the problem isn't with the relay itself. Ground that brown wire and see now if the relay works.

I should pull coolant reservoir probably?

For what reason?

To get to the wires. PCM is on firewall correct?

Yes, right side of firewall.
If you can access that brown wire leaving the fuel pump relay at the PDC, you could ground it there is that is easier.
Did you check all them fuses first?
Is there a check engine or security light remaining on or flashing?

Okay. Thought that was option. The check engine light remains lit, but that has been on for a long, long time.

Well then, there is no way to tell then if something new is making the check engine light come on. You should retrieve those codes but if you cannot, just continue with the testing anyhow.
Did you check all those fuses first?

I checked for continuity, is that good enough, or should I be checking for voltage?

Voltage.

Okay. Should everything be twelve volts. I only have a multi-meter.

Yes, twelve volts with key on run.

Okay, thanks, I will check. Gotta warm up a minute, cold as hell here in Michigan.

Checked voltage with key on. #6 = no power, and #24 = no power. All others mentioned had twelve volts. Also, correction, the check engine light does go out after a couple seconds. Move on to grounding brown wire still?

No, are you sure you had a good ground on your voltmeter? Those fuses are supposed to be hot all the time from the battery.

Just re-checked, same result. #6 ASD fuse, and #24 fuel pump fuse = no power.

And other fuses in that PDC do have power, so the voltmeter ground is okay?
If so, then that is your problem, those two fuses are not getting power. If they all are not getting power and you are sure the ground is okay, check the main feed to that PDC. If some fuses do have power but just not those two or even a few more, then the problem is inside that PDC and could be something shorted out inside it, maybe melted, rusted, etc.
If you could remove it and take it apart, you should be able to see what is going on inside it and it may be obvious, or you could test it with an ohmmeter once it is apart, from the main lug to those two fuse spots.

Should everything in that panel be "hot"?

most them if not all of them . i am not at my PC now to look up the wiring diagram i am on a tablet. but i do believe they are all hot all the time.

Okay, because there were several other of the blade style fuses that were cold. I did not get into all the "ice cube" fuses. I will pull the panel out and take a look inside. burr fourteen degrees.

okay, if all them all not hot check for voltage first at the main lug that feeds that entire box.

I was checking wrong. Everything seems to be hot. Oops. Using main lug as my ground before. Been a long couple days. Now jumper brown ground?

No, what about those other fuses, the #16 and #26, in that PDC? Now for those the key does have to be on run, because it is the ASD relay that powers those.
So there were some in there that were not hot all the time.

I will recheck everything tomorrow and let you know. Getting too dark out to see. Thanks for your help today. I feel like I am getting somewhere. Wife will be happy.

Okay.

Fuse #12 (under dash) = hot
#24 (under hood) = hot
#6 = hot
#16 = 0 volts
#26 = 0 volts

Did you remember to turn the key to run when checking those #16 and #26? If yes, than replace that ASD relay.

Yes key was on. Swapped ASD relay with one from other jeep. No start. Didn't affect other jeep either.

Do you have voltage at them fuses #16 and #26 now with the key on run, after swapping in a asd relay?

No. 16 and 26 are 0 volts.

Ok, I don't believe the fuel pump relay will work until the pcm gets it's power from that asd relay and then fuses #16 and #26, so there is a dark blue/yellow wire coming off that asd relay that goes to pin #3 of the pcm. The pcm has to ground this wire in order to activate that asd relay, so let's ground this wire and turn the key to run and see if that asd relay activates, then powers them fuses 316 and #26 and also now power the fuel pump relay and the fuel pump.
If so, then make sure the connector at the pcm is good and tight. If it is you might be looking at a bad pcm, but first disconnect each end of that dark blue/yellow wire and using on ohmmeter, make sure it is ok. Ballpark ohms is 5 ohms. It should be lessor equal to 5 ohms. If it's more the wire is bad. If it's good, also make sure it isn't shorted to ground so place one end of the ohmmeter on that wire, anywhere, then the other ohmmeter test lead on a good metal ground or the negative battery post, if it will reach and it should read infinity or 1 on some digital ohmmeters. I means infinity.
If it reads anything at all, then it's shorted to ground. If so, replace that wire with the same gauge, color and length. If it comes down to a possible bad pcm, you should at least retrieve the trouble codes first before replacing and programming the pcm.

I'm just about to check those last things you listed. Meanwhile, is there a switch I need to reset after being towed. Everything I have found says no, but the interweb can be unreliable sometimes.

No on a switch reset.

Grounded asd relay, turned key on. Power to 16 and 26. Fuel pump still doesn't run. I'm working on tracing wire to check resistance. Or should I wait, since the pump isn't doing anything.