With OBDI, I don't think you get any more information from the diagnostic tool than you do from doing the diagnostics with the key.
In case you have missed this, on an OBDI Cherokee, you can get the diagnostic codes by cycling the ignition (just ignition, no start) on-off-on-off-on.....then wait and read the flashing of the check engine light. Each code will appear as two flashed digits. "12" will probably come up for a recent battery disconnection, and often appears whether or not it should. "55" is end of sequence, and always appears. Any other code is meaningful. If you have either a factory manual or a Haynes, it will list the codes. It's not that hard to get mixed up with reading the flashes, so run through a couple of times if you have anything unusual, to make sure you're counting them right.
The codes themselves may pinpoint a problem but if there's a wiring fault or something other than a direct failed sensor, it might only give you a general area to hunt in.
In my experience with the 93 and 95, any failure of the crank or cam position sensors, or anything else bad enough to kill the engine should set the check engine light, but it's always a good idea to check the stored codes anyway.
For vacuum, I'd just get a vacuum gauge, and plug it into the manifold port that goes to the vacuum reservoir and heater controls. Crank the engine and see if it develops something approaching the proper vacuum.
I may be wrong, but I suspect the problem is going to be something related to the fuel or the air, and not a sensor.