I've tried searching the forum for this problem but no luck...I was sitting in my driveway today with my 98 Jeep 4.0 running when all of a sudden the temp gauge dropped to zero and the jeep started running rough and when I hit the gas a puff of black smoke came out the muffler...after a few minutes the temp gauge went back up to normal and the jeep ran normal...any ideas? I'm thinking some kind of computer problem? thanks

 

Coolant temp sensor located on the upper hose/thermostat housing. The computor uses the info from this sensor to time the fuel injector pulse width. This is a two wire sensor. More than likly the connector may be corroaded but the sensor itself could be failing. On the older models they had two sensors one on the back of the head for the temp gauge and the one on the therm housing for the fuel metering.

 

When this sensor goes open...(fails) it tell the computor that the engine temp is at minus forty degrees, that is why it ran rough with black smoke.....the computor was trying to give it more fuel for the warm up.

 

thanks alot man...I figured it was sensor related but had no idea where or what...I appreciate the help...I'll let you know if that fixes it