Chrysler Repair: Fuel Consumption, jeep cherokee classic, coolant temperature sensor

Question
Roland, my 2000 Jeep Cherokee Classic started consuming a lot of fuel today. What could be the possible problem. It never did this before.

Answer
Hi Heather,
It depends upon of course whether the fuel consumption truly is increased (based on starting with a full tank, driving a known distance, then refilling; or on a change in a mpg meter reading on the dash) and even that can be variable depending upon whether the driving conditions have changed (average speed, head winds, tire pressure, dragging brake are possibilities). But assuming none of those errors or changes are at play, the first mechanical area to check would be for a fuel leak. Start by looking under the car with the engine idling and see if you see any fuel dripping anywhere from the rear (under the fuel tank) forward to the engine area. Seeing none I would then open the hood and smell for a fuel leak and observe whether any of the fuel lines (that come from the rear and up into the engine compartment near the firewall and to the intake manifold area on top of the engine) show any signs of wetness from a fuel leak. Seeing none, I would then stop the engine and pull out the oil dipstick and smell the oil to see if has the odor of gasoline which would indicate that exceesive fuel is being dispensed thru the fuel injectors and flooding down into the oil pan.  A single stuck open injector can do that, which should be noticed as a "miss" on one of the cylinders. Smelling none, I would notice whether the engine tends to run o.k. when it is first started from cold but then begins to run rough as it warms up. If that were true, I would suspect that the engine coolant temperature sensor has ceased to read accurately and so the fuel injectors are not making the adjustment to use less fuel when the engine is warmed up. There may be a fault such as this which the engine control unit has the capability to detect. On the Chrysler cars you can test that theory by turning the igntion switch "on-off-on-off-on" within a period of 5 seconds, where "on" means to the 'run' position (not all the way to the start position). Then look at the check engine light to see if starts to flash, pause, flash, pause, etc. If so, count the number of flashes before each pause and write them down in the order they readout. Then pair them in groups of two to form two-digit numbers. The last two sets of flashes will be 5 in each, which forms the number 55 which is the code for "end of readout". I am not certain whether the Jeep engine controller will do this self readout or not. If not, then you will have to get a shop to do the readout, give you the code results, and an estimate for repair of the problem stated to be present by the code. You could write back with the result and we can compare notes about the proposed cure before you authorize it. Changing the sensor is a 10 minute job.
Let me know if something interesting reveals itself through this check-out approach.
Roland