heres a good one for the electronic gurus on here... replaced my o2 sensors a week ago, fuel economy went up to 16-17 mpg from 12-14.... back at 12-14 mpg. i can only think of the map sensor, a faulty throttle position sensor or the computer itself is being an ignorant bastard and either prevent the fuel trim from going back to normal * talked to my auto/deisel electrnoics instructor and he said my fuel trim is running way to rich* or what i like to say " the infamous pcm needs to be replaced"... anyone have an idea?.. i commute to college daily, 5 days a week, 60 miles round trip a day, and i work at toys r us which pays garbage [8D].. thanks guys

 

put the originals back in and see if the mileage goes back up... could be that one of the sensors is bad or on the bad end of the "good" scale for the PCM...

 

Did you use OEM or universal sensors? All O2's work in the same way (voltage generating from 0-1V), but do not necessarily respond at the same speed. They could be respondng slow, but just fast enough to notset a DTC. IF it were another component causing it to run too rich, should set P0172 &P0173. Butyour fuel economy change suggests it mightbe right on the edge of that ~20% fuel trim most PCM's allow before setting a rich or lean code.

A cheap way to figure out if it's actually rich going down the road is an air/fuel ratio gauge. Autometer has units that run ~$60. All you do is supply them with ground, key-on power and tap the signal wire for an o2 sensor. It's about the only way you're going to know if your A/F is stoichiometric as you're driving day to day. Normally, they bounce constantly from lean to rich when cruising. But if yours hangs out too much on the rich end, you've got an issue.

 

another thing to ask is do you have the o2's in the right locations... my '00 ram had 2 different p/n's for front & rear. the rears are setup differently IIRC...

 

the new o2 sensors are oem... last night my fuel milage went back to 16 after filling up and doing the hand calculating. still not good.. im going to look into A/F ratio gauge. im going to crawl abck under my truck later today and check out the o2 sensors connections, make sure if any have come undone, thanks

 

your complaining about 16??? park it and drive the Yaris...

 

Accurate fuel economy calculation is going to require at least two fill-up's, preferably having run the first tank as low as possible.

That said, it seems youare on the low end of what is achievable. Check your fan clutch, as one that isnot slippingcan significantly reduce fuel economy, especially on the highway.