How do I correct bad gas mileage in 1993 Dodge Dakota?

It does sound like you are running "open loop" meaning the ECM is not controlling timing when the engine is hot.

Likely candidate might be the engine thermostat is stuck open which is how they usually fail, stuck open. It would be difficult to notice in the hot summer months since you are not running the heater or defroster. Or possibly the engine temperature sensor is shot.

The O2 sensor should set a code in the ECM if it's shot. The recommended service interval for O2 sensors is 100K miles or ten years. I seem to recall that the fuel efficiency increase is around 5%+ with a new O2 sensor.

You can also test the knock sensor but if the engine feels smooth and the only thing that you can detect is bad MPG's, then you can suspect the MAF, MAP, temperature sensor, thermostat, knock sensor. There is a specific test for each one that you can find in the Hayne's book on computer codes. It tells you how to trouble shoot and test each sensor.

The other thing would be if your transmission is NOT shifting into OD. Then you'd be driving a 3 or 4 speed tranny without the benefit of the OD lock-up solenoid when your between 35-45 MPH so you'd never hit the 1:1 ratio and save fuel. Most lock-up solenoids fail or stick because people neglect their transmission service every two years or 25K miles and the metal residues build up and cause a sticking OD solenoid or a sticking valve in the valve body inside the tranny.

Good Luck!

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How do I correct bad gas mileage in 1993 Dodge Dakota?

How do I correct bad gas mileage in 1993 Dodge Dakota? I'm only getting 10 m.p.g. and it seemed to happen overnight...from 17 to 18 m.p.g.

The engine compression is good. The coils are good. The cat converters and exhaust are solid. The timing is right. I'm on my third tank of...

You need to fix the running rich condition. Do you have a multi meter? If so with engine hot and cold check the resistance of the engine coolant temperature sensor hot and cold. If resistance is out of specifications replace the sensor. If the sensor does not read accurately telling the computer that the coolant is at a certain temperature such as the coolant is cold while it is hot out side. Then the computer will richen the mixture until it see's different. If the sensor checks out get a can of brake cleaner and spray a round the throttle body while engine is cold and running. Spray vacuum lines and hoses and if the truck idles up or down or stalls then where you have sprayed there is a vacuum leak. The reason for this test is to make sure there are no vacuum leaks, because if the computer senses un accounted air coming in. Then it will compensate and richen the fuel system. With air cleaner off assuming you have throttle body injection, watch the fuel injector and see if it leaks. If so remove the injector and replace the injector o ring. If you see the injector leak it self replace the fuel injector and its o rings.

Is the motor up to operating temprature. If not, it is running in open loop, and will be harder on gas. If it is running cold, or the temp sensor has failed, the computer default to open loop. Hope this helps.

Agreed on making sure the engine is up to proper temperature.