where did my mileage go

[DaveWC]

I'm sure this isn't the first time it has been asked, but I seem to recall getting 19-20 mpg when I first got my 97xlt. It had 85k then, has 172k now. Only mod made is K&N style air filter. I have checked it with an OBD2 reader on my lap top, no SES lamp, seems to run ok, though I do remember the O2 readings on the laptop being lean both banks. Is this the problem? I thought if the 02 sensors were bad, SES lamp would come on. I understand that if the 02 sensors are telling the ECM "lean", the ECM adds more fuel to correct the problem. I just need a little more input so I know I'm heading in the right direction. Thanks, great forum!! DaveWC

 

[unclemeat]

Perhaps, you fuel has changed. Ethonal enhanced gasoline does not get as may miles per gallon as pure gasoline.

You may also have a change the gasoline. In larger cities that do not reach EPA standards for ozone, the gasoline is reformulated or oxygenated. When that fuesl was introduced here wel lost 10 to 15
% of our fuel mileage overnight.

 

[BLKLTDV8]

O2 sensors go bad slowly, and are considered a wear item. They have to be pretty bad to put the CEL on, or failed altogether. I would change out those O2 sensors along with cleaning the MAF and throttle body along with changing the spark plugs.

 

[aldive]

Before you go changing )2 sensors, confirm that they are indeed bad by scanning their function.

I would love to have a dollar for every perfectly good O2 sensor that was replaced needlessly.

Good luck ....