Bad Gas Mileage [Merged 9-6]

[99GST]

I am still getting some pretty bad gas mileage.

I am only getting about 19.7 mpg with mostly city driving shifting at 4k.
I have already replaced my front O2 sensor and am looking to replace the fuel filter.

I have a 99gst with about 55k miles on it. Should my fuel filter already be bad?

What else should I check or change? I have NKG plugs and Accel wires are on the way.

Thanks,
Nathan

 

[Lightnintko]

mine had the same prob. it was the main 02 sensor (the one in the turbo 02 housing

 

[spyderdrifter]

My upstream o2 was bad as well as the gauge. My scanner showed the fuel trim though.

 

[Maroon98gst]

But if it was the o2 sensor wouldn't there be a light on

 

[gho5tone]

No not really. When my o2 sensor went out, mileage decreased and it ran rich. Of course every situation is different.

 

[spyderdrifter]

My CEL never illuminated when my O2 went out. The only way I was able to tell was with the scans from my scanner and knowing what the readings meant.

 

[Supra Mario]

Try a tune up if nothing else.
Boost leak test,
Spark plugs and plug wires,
Maybe cleaning throttle body and whole intake would helped a little(helped me)
More than likely O2 Sensor if you don't have a CEL.
I'm in the same situation trying all this stuff. Filled my tank and was down to 1/4 of a tank in 80miles.

 

[Maroon98gst]

I'll check the o2 sensors

 

[MasterMatt209]

I have a 98 GSX automatic. I'm getting under 200 miles per tank which to me is horrible gas mileage considering its a 4-cylinder. Not sure if something is wrong with my car or what? Anyways I was wondering what are some upgrades or anything I can buy for my car to increase gas mileage

 

[Dsmkauai]

When's the last time it was tuned up? You have any check engine light? Could be a falling O2 sensor or bloost leak.

 

[MasterMatt209]

No tune, not sure where I should go to get one, no check engine

 

[Dsmkauai]

I would start with changing. Plugs, plug wires, airfilter and oil filter, and Pcv valve. Pretty basic tune up stuff.

 

[MasterMatt209]

I've changed the oil, new plugs and wires I think I'll change the pcv valve as you said

 

[2gGst98]

I'm fwd but,
How are you driving, when I drive hard or I'm boosting more then other times I can get about 175-200 miles to full tank. When I drove 487 miles 2 weeks ago at 63 mph, I got 38.3 mpg. I didn't think would get that good. On the way back I wasn't so conservative and got little less then 12 mpg, 13 psi 14b. Stock fuel at that time. Saved only 30 min also not too worth it . Food for thought.

A lot of conservative city driving your going to be around 20mpg give or take a few, probably take, Would be my guess. So reset your trip when you fill up and divide miles by how many gallons you put in and see where your at.

But I hope this gives you an idea. Sounds kinda normal to me

 

[MasterMatt209]

Thank you so much that's a great idea, I'm probably gonna fill up today and do that and drive extra conservative to see what kind of mileage I can get, steady throttle best way to go?

 

[luv2rallye]

Make sure your upstream O2 sensor is working properly or you will stay in open loop mode and get terrible mileage. http://www.gnttype.org/techarea/ecmsensors/O2sensors.html

 

[MasterMatt209]

That's another question, how do I check an o2 sensor? Also where is that one located

 

[Dsmkauai]

Get a scanner that can stream the O2 signal. Then you can watch it and see if it's stuck or moving.

 

[MasterMatt209]

Sorry for all the questions but where can I get something like that

 

[NY 95 TSI AWD]

A simple palm pilot logger setup would tell you. It's a good diagnostic tool. You can see what the check engine lights are saying and see the outputs of senors, water temp, ect.

 

[jbeaton9292]

Its a 2g so its an obd2 car i would suggest to you a elm 327 scanner you can get one for under 10$ on ebay its a bluetooth adapter that plugs in and get on your phone assuming you have a smartphone torque pro its i think 4.99 and you can log everything you need with it and check trouble codes i have 13$ into my setup for logging granted i dont have my dsm anymore but i used it to tune my 2g with an safc and worked great one of the best investments i made for that car and i still use it for engine lights in curtent car or friends cars so on

 

[MasterMatt209]

Its a 2g so its an obd2 car i would suggest to you a elm 327 scanner you can get one for under 10$ on ebay its a bluetooth adapter that plugs in and get on your phone assuming you have a smartphone torque pro its i think 4.99 and you can log everything you need with it and check trouble codes i have 13$ into my setup for logging granted i dont have my dsm anymore but i used it to tune my 2g with an safc and worked great one of the best investments i made for that car and i still use it for engine lights in curtent car or friends cars so on

That sounds perfect thanks for the help guys I will do this for sure!

 

[jbeaton9292]

That sounds perfect thanks for the help guys I will do this for sure!

No problem its a great tool to have for these cars

 

[VegasTuner]

Mine gets about 200 miles per tank