[BTCruiser]

My 97' LC (~170K) had a sudden gas mileage drop (from 15mpg to 9mpg) since 3 tanks ago. No other problem observed. I do smell the odd at the exaust, but it has been like that for last 1.5 years. Spark plus has not been replaced for at least 30K miles. New air filter, up-to-date oil change, and 0.5 psi higher than required. Anyone can help with some suggestion I can look into? Thanks.
(I towed a 6'by12' Uhaul carrier, running 2300 miles 3 months ago w/o any problem.)

 

[BTCruiser]

update: I changed spark plugs, no improvement; and just changed PCV valve, if it does not help, what is next thing should I check? Oxgen sensor?

 

[arabianobsession]

Check 02 Sensor....and your catalytic converter.

 

[BTCruiser]

Check 02 Sensor....and your catalytic converter.

But I don't have any DTC code. Does this mean o2 sensor should be functional? Thanks.