If it starts no problem when it's cold but won't start without pumping the gas when the engine is hot, it is most likely the engine temperature sensor. Check the wire going to the sensor, pull the end off, clean it really good, and plug it back in. This fixed my 97 cherokee. It's quite possible the sensor has gone bad, but I bet the connector is just dirty.
The link below goes to a write up on testing the sensor.
Hope this all helps.
Rich
http://www.autozone.com/servlet/UiBr...3d801523cb.jsp
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The engine coolant temperature sensor, or ECT sensor is mounted by the thermostat and provides the PCM with engine temperature information. The PCM supplies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the PCM monitors a low signal voltage which it interprets as warm engine.