my car is running really lean 18-1 F/A mixture and its really hurting gas mileage right now and i cant seem to figure out why its doing that... any ideas anyone?

thx

 

Have you changed the O2 sensor? How old is the O2 sensor?

Also, have you done the usual maintenance stuff, like fuel filter, air filter, plugs?

BTW: typically a slightly lean mixture at highway speeds would result in better fuel economy. But 18:1 is too lean.

 

the air filters and fuel filter is new, the mechanics said the o2 sensor is fine but im not sure because the car sat for a really long time before i bought it.

at the end of the month im going to put new plugs in it and an o2 sensor and if it doesnt work i`ll post back.

thx

 

As a base point what was used to determine the AFR?

 

im not sure what they used to figure it out but i`ll get back to you on that

 

Please do. Unless they are using a wideband (doubt it) i would question their accuracy. Being a 18:1 AFR i dont see how that would be causing that much of a loss of gas mileage. I can understand it causing bad gas mileage giving that something is off, but not enough to be causing a significant or noticable loss.

 

If you're using a cheapo af meter that just reads the normal O2 sensor, then your problem could be the O2 sensor, because if it's showing false lean, the ECU will overcompensates rich, and thus screw your mileage.

 

I had a similar problem with my car with the ECU overcompensating for a lean condition. It turned out that the air pump diverter valve was busted, so it was still pumping air into the exhaust manifolds instead of down to the cat once the car was running in closed loop. This can also cause the oxygen sensor to detect a lean condition. I'd have never found the problem if I hadn't taken it to a friend of mine who's really good diagnosing efi motors. Just something else you might want to check while you're at it.