Sudden drop in performance and gas mileage

ronjon27

I have a 2000 Jeep Grand Cherokee 4.0, 6 cylinder. My car, intermittently has a sudden drop in performance and gas mileage and the exhaust fumes have a very distinct & strong odor as if it is burning very rich. My gas mileage goes from about 20 mpg (highway) to about 4 to 6 mph. it will remain this way for a long time and then suddenly, it reverts back to running normal. Can any suggest a possible cause and fix?

Thanks

Ron

Mr_Shiftright

What you'll have to do, or have done, is to scan the car while it's in its gas-eating mode. The scanner would have to be sophisticated enough to capture the data stream, so that the technician can interpret it and find out which sensor or module is going wonky on you. Such a rich mixture could be quite harmful to your car's catalytic converter, so I'd get on it if I were you. Some wild guesses might include a bad coolant temperature sensor or defective fuel injector. I don't think a defective 02 sensor would allow such an extreme deviance.