Have a problem with my 1994 Jeep Cherokee, when it is Cool in Teperature runs great when it gets above 75* at slow speeds it starts running rough and when parked will not start. We pull the sensing unit at the thermostat and it starts, had flow check on water and all is OK there. Replaced sensor at thermostat and another one at the back of the engine on top, replaced electrical component in the distributor under rotor, anyone run into this problem befor or have any ideas what the problem is??/
gduke33@verizon.net

 

When was the last time you've had a tune up? (Champion copper spark plugs gapped to .035, quality spark plug wires, distributor cap with brass contacts and ignition rotor)

Check fuel pressure at the fuel rail using a fuel pressure gauge.

Also, your crankshaft position sensor is a huge suspect here. How many miles are on your XJ? That sensor usually craps out at around 120,000 miles or so