2G Very very poor gas mileage

91dsm · Sep 23, 2014

I just bought a really nice 97 gst in good shape and I was driving it home on the highway and I realized when I got back I had got a whopping 12 miles per gallon. I have little experience with turbocharged cars. Its pretty much stock except for an mhi evo 3 turbo running on 15 psi and a 1g talon bov. Also the guy I bought it from decided to get rid of the cat. My only guess is that maybe he didnt properly bypass the o2 sensor and it could be the cause of my mileage but the cel isnt on to throw a code for any sensors so I doubt thats it. Any suggestions as to what this might be?

jimsgsx · Sep 23, 2014

Have you done a tune up? Its definitely not because of the o2 sensor located by the cat. That sensor just reads the air leaving your car and wouldnt cause that bad of gas mileage. Is your car running very poorly. Need more info on your car.

91dsm · Sep 23, 2014

jimsgsx said:
Have you done a tune up? Its definitely not because of the o2 sensor located by the cat. That sensor just reads the air leaving your car and wouldnt cause that bad of gas mileage. Is your car running very poorly. Need more info on your car.

The car feels like its running completely fine it pulls nicely and definitely isnt lacking power. If it is a tuning issue roughly how much is this going to cost me?

jimsgsx · Sep 23, 2014

If you take it to a shop its not gonna be cheap probably around 5 or 6 hundred. Thats the prices where i live anyways. Im not a dsm owner who keeps upgrading. Ive done little to my car because i like the way it drives now, so i havent dealt with tuning really.

91dsm · Sep 23, 2014

jimsgsx said:
If you take it to a shop its not gonna be cheap probably around 5 or 6 hundred. Thats the prices where i live anyways. Im not a dsm owner who keeps upgrading. Ive done little to my car because i like the way it drives now, so i havent dealt with tuning really.

Wow I really hope thats not the case but I wouldnt be surprised looks like I got another craigslist special. And im assumed its not safe to drive the car with the engine running this poorly.

jimsgsx · Sep 23, 2014

I would do a tune up. It never hurts. New plugs, oil, the usual.[DOUBLEPOST=1411462635][/DOUBLEPOST]I bet you need sparkplugs changed. New plug wires. Hows your air filter looking? Trust me the first thing you do is a tune up.

nathan_spindler55 · Sep 23, 2014

try and get it hooked up to a diagnostic reader and see if anything shows up. bad o2 would cause bad gas mpg. i have something wrong with my knock sensor and its affecting my mpg as well and my car pulls great but i know it will pull better when its better. make sure you have good ngk plugs and gap them correctly also.

thomcasey · Sep 23, 2014

Also, if you are new to turbo cars, you must know that your right foot can greatly affect gas mileage. How often did you "get on it" after you bought it? also, was the drive completely highway or was there some city in there?My Colt gets 38mpg on the highway and 28 combined city/highway. BUT, I can easily coax lower than 20mpg with the boost lever.

rough · Sep 23, 2014

thomcasey said:
Also, if you are new to turbo cars, you must know that your right foot can greatly affect gas mileage. How often did you "get on it" after you bought it? also, was the drive completely highway or was there some city in there?My Colt gets 38mpg on the highway and 28 combined city/highway. BUT, I can easily coax lower than 20mpg with the boost lever.

I get on it a bit! I live really close to work here on the NW side of Indy, so most of my driving is below 45 with stop signs and lights galore!
I get a horrible 160mi to the tank! My GS DD got me to and from work 3 times a day 5 days a week for 2 weeks on a full tank, where the GST makes it the week, but wed I'm filling back up!
Small price to pay to have a little fun!

91dsm · Sep 23, 2014

thomcasey said:
Also, if you are new to turbo cars, you must know that your right foot can greatly affect gas mileage. How often did you "get on it" after you bought it? also, was the drive completely highway or was there some city in there?My Colt gets 38mpg on the highway and 28 combined city/highway. BUT, I can easily coax lower than 20mpg with the boost lever.

I went very easy on the car and they were all highway miles.

mercaholik · Sep 24, 2014

Exactly only the upstream o2 sensor will affect gas mileage, not the downstream. But that will give you bad mileage, i would put a new ngk just cause. If you have a logger or scan tool you can watch for proper cycling from o2 and short and long term fuel trims.

DSM Chase · Sep 25, 2014

Its simple, if everything is fresh in working order, stock fuel components and tune, fresh plugs, oil,etc. STOP boosting the car and making pulls expecting to get gas mileage, and you'll only get about 20 and that's granny shifting.

91dsm · Oct 17, 2014

DSM Chase said:
Its simple, if everything is fresh in working order, stock fuel components and tune, fresh plugs, oil,etc. STOP boosting the car and making pulls expecting to get gas mileage, and you'll only get about 20 and that's granny shifting.

Well I found out the problem I went to change the timing belt and found out one of my belts was off by a whole notch. I guess whoever did the previous belt installed a belt incorrectly.

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2G Very very poor gas mileage

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