poor gas mileage update

[pmkls2]

Well, to refresh everyones memory I have had an issue with my 1990 240sx using too much gas. I had replaced many sensors and tune-up items with no success. I was advised to check my airflow meter and I did and the readings on the three terminals were 14v-.02v-1.51v warmed up at an idle. I ran an additional ground wire for it and noticed a difference in the way it ran, but the voltage on the signal wire was still a little high. I have ran about 2 and a half tanks of gas through my car since and to my disappointment the gas mileage has seemed to stay the same. I am still getting about 300-330 miles on 13.5 gallons whereas when I bought the car a year ago it was 350-375 miles on 12.5 gallons. I am curious if 1.51v warmed up at an idle is high enough to warrant replacing the meter and more importantly will replacing it help fuel mileage? any and all comments are greatly appreciated.

[Q45tech]

The exact voltage in the acceptable range depends on rpm.

You need to measure the oxygen sensor cross over counts making sure you have 5 per second at 2,000 rpm.

What is compression and leak down of each cylinder as mileage adds up MPG can decrease if you are near the compression low limits [efficiency drops].

[kreepa]

holy crap are you serious?!?! i only get like 250 IF im lucky running it almost dry... i have somewhat of a leadfoot but i don think it should make THAT big of a difference

[pmkls2]

The 1.51v signal is at about 900 rpm idle. As far as cylinder leakdown, I would say that may play a little into the equation because I have driven the piss out of the car in the past year, which I have also managed to put 30k miles on it in that time period. However, I have never had a car that was effected by mileage like this one. I have never owned a nissan either though. And by the way for creepa, I run the engine to redline between shifts almost all the time, but I always have driven it the same.

[NISTECH]

how is your tire pressure/ condition? is yoour oil level/ condition good? at 900 rpms you may get that 1.5 volts at idle. your base idle should be around 700 base idle.

[pmkls2]

The oil level is full and the tire pressure set at 35psi. I have no idea why the idle is 900, but I have cleaned the idle controls and the throttle plate before. I have also previously replaced the tps and it is set at .5 volts at idle warmed up. It has always idled this high though. I dunno, this car has always puzzled me though. Thats why I sometimes miss my carbureted T/A. By the way I usually only go 1500 to 2000 miles on oil changes as well.