mpg help

[toddomen]

I have 97 grand prix 132,000 mile filled up with 87 grade gas and did the
math and got 16 mpg in city and 18 on hwy i have done a tuneup when
i bought the car at 130,00 mile

[CrazyHorst]

Couple things to check...1) compression on all 6 and 2) that you are in closed loop and the O2 sensor is "toggling" as you drive (the signal would be a sort of sine wave if plotted against time).

I'm guessing if you had SES codes you'd be posting them or about the light being on.

If you drive in the mid 80s hwy the vehicle will go into open loop for catalyst protection. If the coolant temp is thought too high or low by the PCM you will go into open loop. If the O2 sensor signal is pegged this also triggers open loop. Closed loop is far superior for best fuel economy.