Re: 88 Cherokee no spark
The early Renix type 4.0ls will run and start with the distributor sensor disconnected, but they will need a longer crank time than usuall and sometimes have a hesitation. Unplugging the sensor causes the EFI system to go to a simultanious injection pulse instead of the sequential pulse that is normal.
Sometimes, a shorted cam "sync signal generator", as it is called, will cause a no start, unplugging it will isolate it as the cause or not.
More likely, the PCM or wiring problem is the cause. The large bulkhead mounted connector, near the emissions label on the cowl of '87s and '88s, is usually full of corrosion, bypassing it by soldering together each wire on opposite sides of the connector or replacing it with the '89-'90 style harness
is the way to fix this problem. Soldering the wires wont cost much more than the time, the new replacement harness costs over $400.
The PCM , we usually test by replacing it with a "tester" we keep in the shop.
Rebuilt ones are available at the dealer and from the aftermarket. Double check the power and ground circuits to the PCM, the shop manual should have a schematic. You may have a bad ignition switch, blown fuse or fusable link.
When you replaced the crank sensor, you did install the jumper harness that goes directly to the PCM, didn't you? This is very important to install on the '87 and '88s, and recommended on the '89s and '90s too.
The MS 1700 tester went out with the '80s, replaced with the DRB2, only a Chrysler/Jeep dealer will likely have this unit. Using it would help pin down the problem, in most instances. Most dealers will want to charge an hours' labor for a diagnostic test. This may be money well spent before replacing expensive parts that you can't return.
Hope this helps, good luck!