I have a 98 jeep grand Cherokee Laredo and whenever I crank it it will cut right off. Sometimes I'll get going down the road and then It will cut off. It cranks right back up after it cuts off though. I've already had the computer replaced in it.
Any ideas as to what else I could try?
(1) You are replacing a lot of "spark" related parts. So, does this mean that you know the problem is "spark" related? Were there codes you read from an ODBII scanner? Given what you are replacing - battery, alternator, coil, PCM, wiring - it seems like you suspect spark cut-out or someone read a P0351.
(2) If you don't "know" it to be a spark problem, another common issue of cut-offs is a fuel issue (pump or filter). Have you placed a fuel pressure gauge on the rail and observed behavior during your stalls?
If it were my Jeep, I would put a fuel gauge on it just to rule that out.
If you saw a P0351, then I'm pretty sure that this is set when the PCM coil driver notices that there is not spark. Here's some things it could be ...
Your PCM is bad. Now, if you have replaced your PCM with no change in behavior, then you can rule this out ... if you had the problem a long time ago, then it went away after replacing the PCM, then it is now returning. Well ... it could be the PCM again.
Your Crankshaft Position Sensor is cutting out on you ... the PCM will shut down the engine if this sensor cuts out, and failures can happen after 100,000 miles. My observation, however, is that most people who have a failed Crankshaft Position Sensor can not even get their Jeep started.
You have bad wiring somewhere (broken/shorting/etc) ... jiggling the wire harness will tend to reproduce the cut-off problem.
You have a short or a voltage problem somewhere on the +5 supply from Connector #1. The +5 voltage on a '98 supplies the MAP sensor, the Crankshaft Position Sensor, the Camshaft Position Sensor, the and the TPS. I'm not sure if the +5 of Connector #1 is isolated from that of Connector #2, but the +5 of connector #2 goes to the Transmission Solenoid and the Speed Sensor.
The ASD relay is having erratic operation. These can get weak over time. An easy test is to switch the horn relay with the ASD relay.
It is rare, but if you have installed some of those fancy new spark plugs - something other than a simple copper one - they can create voltage spikes when they fire, and these travel back through to the PCM's coil driver and the 12 volt supply. It can cause a PCM to reset. Your PCM was designed during a time when spark plugs were just simple things ... your Jeep'[s PCM just needs things to stay simple and OEM.