89 jeep Cherokee won't start

I have an 89 jeep Cherokee. Has spark and
fuel won't start. If I unplug the crank sensor
it's cranks smoothly but if I plug it in, it's
cranks like the battery is dead then evens
out then lugs then evens out. Brand new
starter and battery I've tried 3 different
crank sensor and no change. Timing and
compression is good. I need some ideas to
try this has me baffled