ok before i got my cat back i was averaging 11-12mpg city, and 13-14mpg highway. well after i got my cat back i averaged 17mpg on the highway, then i got back home and filled it up and am now getting 9mpg city!! What gives????????? the plugs and O2 are only 3500 miles old. just chaged my oil the day of the trip. the only thing i did differant was put in a higher octane gas (89 instead of 87).....could it be so low cause i didnt really drive it far? i mean i live 3 blocks from my work, so the car never gets warm really. but still before it wasnt that bad.....im stumped, i hate getting that bad of gas mileage.....any thoughts?? check sig for engine.
Supreme Member
Well, it might be the short trips, if that is all you are doing. I'd check to see if everything is still hooked up correctly to the carb and whatnot.
Most of the time a reduction in backpressure, like your new catback, will make an engine go lean, if anything
Most of the time a reduction in backpressure, like your new catback, will make an engine go lean, if anything
five7kid
Moderator
close
May 4, 2026
(17+9)/2 = 13.
Over the two tanks, you got what you used to get. When you thought you got 17, you just didn't fill the tank all the way. The next time, you did.
Over the two tanks, you got what you used to get. When you thought you got 17, you just didn't fill the tank all the way. The next time, you did.
i always fill my tank all the way when i do my MPG observations. fill it to the top, drive it till its near gone, subtract the mileage, then divide by the gallons.
five7kid
Moderator
close
May 4, 2026
So do I. I even record it each time in a little spiral notebook I keep in the car.
It still happens to me from time to time. Especially when I get gas at a place that I don't normally frequent. Or, when the apron is sloped so the tank doesn't fill properly.
Oh, last tank was low because I charged the A/C - sat at an idle for a long time, no mileage logged on the odometer.
Check it over a couple of more tanks, see if it changes.
It still happens to me from time to time. Especially when I get gas at a place that I don't normally frequent. Or, when the apron is sloped so the tank doesn't fill properly.
Oh, last tank was low because I charged the A/C - sat at an idle for a long time, no mileage logged on the odometer.
Check it over a couple of more tanks, see if it changes.
im workin on that. i was just seeing if anyone thought that a part went bad or something. maybe my car doesnt like 89 octane, lol... the weirdest thing is that i THOUGHT that i was getting awsome gas mileage. i mean i filled it last sunday, and drove on it till yesterday. that doesnt happen much, but then again, i didnt drive around that much either. only 119 miles for 12 gallons 
ps. its really 9.9 something, so its damn close to 10....but still crappy!
ps. its really 9.9 something, so its damn close to 10....but still crappy!