1998 Jeep Cherokee cranks but wont start

When the problem occurs have a helper crank it, while you visually check for spark at the plugs. If no spark, check primary voltage to the coil, engine cranking, dark green wire with orange tracer. Also, check for voltage at the same color wire at injectors. If no voltage, engine cranking, the computer may not be grounding the asd relay for some reason, maybe cam and or crank sensor. Can you check trouble codes? There could be other issues with the relay, wiring circuits? Any suspected sensor issues, check the wiring circuits, first.