Ok this is for my friend's car...it's an Olds Toronado with a 3800 V6. His car gets 16 mpg on average, according to the computer. He's never changed his O2 sensor. The car also smells very much towards the rich side when it's idling or accelerating with the windows down...it really starts to stink up. We put on the instant gas mileage thing and it read as low as 5 mpg during a light acceleration. He threw a check engine light...so I figure it'll be an O2 sensor rich code. Instead, it's a code 44-O2 sensor LEAN. I've never heard of a computer TELLING you the car is running rich, when you're able to smell that the car is running rich, but then have the computer also tell you you're running lean! What is wrong with this picture?! I assume his O2 sensor is just freaking out and making the entire system go haywire...has anyone seen this before? I'm advising him to replace it of course...I'm just curious. Thanks all.

 

think about this.

if the car THINKS the engine is lean.. what does it do?

add more fuel.

thats why hes running rich... the computer thinks hes running lean.



id change the O2 sensor.

 

Ok I'm an idiot--I was thinking that the computer determined mileage partially using the O2 sensor. It was late ok! It determines mileage by the amount of gas left in the tank and how many miles it's driven since the last fill, assuming the counter was reset.... But anyways, I still told him to buy a new one the next time he had the chance. He spent the rest of his money on buying a conical filter for me to rig up on his intake.

 

Those things actually calculate the "insantaneous" gas mileage by way of knowing the injector pulse width, and therefore the amount of fuel being injected, since that's under complete control of the computer.

One would expect low instantaneous gas mileage indication during acceleration; the engine will be in a lower gear (more injector pulses since there's some fixed number of pulses per engine revolution) and calling for some amount of power enrichment (wider pulse), ending up with that much more fuel per distance the car travels.