Buick 81 code 44

I have a 1981 buick skylark 2.8 engine it has completely overhauled motor when tested exhaust it is about 13 to 1 in open loop 14 to 1 closed loop I now am getting intermittent code 44 when slightly up hill when down hill or decelerating light goes out sometimes light is not on for a long time I had run for a while with 10% ethanol and this seemed to cause light to come on more of the time. Is this something that would really need attention as it does seem to be getting much more than 22 mpg on the highway if I test the exhaust again and find reading of 14 to 1 one could ignore problem could one not? Also a code 44 and poor gas mileage can not go hand in hand can they? I never owned this car when it was new, but it runs a little different in the closed loop like it is doing something to the distributor or fuel mixture is this normal as it runs real smooth without computer?

John

Once in closed loop it will run leaner, and ethanol leans it down more, it is possible that the primitive fuel controls cannot compensate for E10, I would run it that way or replace the o2 sensor as it could be skewed by age.

Maybe my understanding is wrong from what I have read sounds code 44 means it is ready lean mixture so it dumps more fuel in. I could have a vacuum leak so I will have to check everything and follow the book on diagnosing this problem.

An old sensor can provide wrong inputs to the ecu, for 20.00 replace it.