Hello Ammo Troop,

My 90 Ranger had declining fuel economy. The High was about 27 for Freeway Only driving, and went down to about 16 with the same type of driving and with a Check Engine light. The code represented a Lean condition.

To make a long story short, I guess that as the oxygen sensor ages it becomes "less sensitive", therefore it keeps adding more and more fuel to satisfy this "less sensitive"condition. It will do this until the sensitivity is so low that it is allowing the injectors to provide a maximum amount of fuel to the engine.

The next step is that the sensitivity of the Oxygen Sensor goes even lower to a point that it turns On the Check Engine Light. In my case the engine was blowing Black Smoke and was reporting a Lean Condition.

Once I replace the Oxygen Sensor the problem went away immediately and my fuel economy returned.

I do not know if this can help for your situation. Many on this site are Eons ahead of me in knowledge about these vehicles. But this was one of the things that I had a problem with about 2 years ago.

Best of luck

Gary