Symptoms
The engine dies when hot and won't restart until it cools, cranks without spark, or the fuel pump won't run. Comanche Club owners name the crankshaft position sensor (CPS) and the Renix fuel-pump ballast resistor as the usual culprits, and say to check the body grounds first for strange electrical faults.
The fix, step by step
- Test before you buy.
- Clean and tighten the engine, body and taillight grounds, and the ground at the fuel tank.
- Then test the CPS hot, right after a failure, with a multimeter against the resistance values for your year.
- On Renix trucks, check the ballast resistor; a jumper wire from the battery to the pump circuit will prove it at the roadside.
- Replace the failed part with one for your exact year, because the parts changed for the 1991 HO system.
Tools & part numbers
- Self-ranging multimeter
- wire brush
- dielectric grease
- long extensions
Where to buy the parts
Crown 33000682 fuel pump ballast resistor, 1987–93 XJ & MJQuadratec ↗Amazon ↗
XJ/MJ crankshaft position sensors (choose by year)Quadratec ↗Amazon ↗
Comanche ignition and sensor catalogRockAuto ↗
Hunting a used or discontinued part? Search eBay Motors for Jeep Comanche MJ parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.