1988 Cherokee with no Spark

[jeepcrazy5722]

I have a 88 Cherokee w/ I6. About once a week it won't start. It cranks but there is no spark. I have replaced the following with new parts: Ignition Coil, Crankshaft sensor, B Latch relay, distibuter, distributer cap, plugs, and wires. I have replace the Ignition control unit with 2 that i pulled from the wrecking yard. Any other ideas? I am wondering if the ECU is the problem. Has anyone else had this problem?

 

[jeepcrazy5722]

Update:

I cleaned the ground wire on the block, it was pretty dirty. That seems to have cured the problem. Apparently the the crank shaft sensor needs enough of a signal to determine top dead center, since the ground was dirty it did not create a strong enough signal.