90 xj NO START

90 jeep cherokee, inline six, automatic

Having some big issues in my opinion....I CANT GO ANY WHERE IN MY JEEP!!!
so i was driving down the road and it dies on me. tried jumping didnt work so we brought it back to my place and have been slowly looking nto stuff....heres the deal
turn the key to start and every thing ges normal like it should
crank it over and it fires up
let it go back to RUN position and it dies immediately
NO IDEA AS TO WHAT IS GOING ON PLEASE HELP

have changed out the ignition switch on the back of the column
some body said change out the ballast resistor so i did that
still in the same hole as before
i checked the crankshaft positin sensor (was another idea) was pretty dirty so i cleaned up down there and re intalled a new one
Nothing has worked and could use sme advice....any ideas
Thanks-
MUDDYMOPAR

Were the connectors for the CPS clean, or did you check? If that connection becomes contaminated, it can cause trouble for you - even if the sensor is good.

The engine will not run without a valid CPS signal - which is why I also advise you to check the connector. Since you're saying it's starting otherwise normally, we can assume that the start motor relay is good, and that the distributor is good (there is a SYNC sensor in the distributor, but RENIX will run without a valid SYNC signal. I've tried.)

You said you also changed the CPS outright - were there any burned-through spots on the wiring jacket for it? I've had that happen - the signal would short out against the exhaust manifold, and would pick up again once the wires came off the thing...

just throwin this out there...

fuel pump relay
b+ latch relay?

good luck.

x2 on relay that is exactly what mine did swap the two midle relays on the passenger side under the hood in the row of four togeather . if it starts go buy a fuel pump relay