23 hwy, 11 city
 

i could use some help troubleshooting this fuel economy issue. for the past 4 or 5 months, probably longer, when ever i've burned through a tank strictly highway or strictly around town i get crazy good highway mileage or unbearable city mileage. both mpgs are beyond what the EPA sticked noted. any ideas?

Only thing I can think of is it running lean. Does it get hot at all or warm up fast?

thanks for your help. hmmm, now that you mention it, the heater does not seem to be putting out as much heat, but its close to normal. and i've a suspicsion that the temp gauge is not rising as high as it was a year ago. i replaced a leaking water pump about 4 years ago, and the lower intake manifold gaskets about 3 years. during one or both of those, i put in a new 'stock' thermostat.

anyway, despite my suspicions about the engine running cool, when i actually counted the ticks on the temp gauge a few months ago and looked of the 'normal' temp, it was actually within limits. i know the various thermostats have different temp ranges. not sure which i put in, so i can't be sure that the temp is within spec for what the one i actually installed.

if i drive downhill for 4 or 5 miles, or if i let it idle for a while in neutral, SES will lite up, then clear itself after a few normal trips. the codes is something like P175, O2 sensor, bank 2 if i remember correctly.

when the engine is warm and at op temp, it'll give one little backfire or something when i start it. this doesn't happen all the time. maybe once a month for the past 4 or so months.

Yeah sounds like one or more of the O2 sensors are faulty. Pull the codes again to see which ones exactly.