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

 

[rob1621]

ok wtf i have 129000mi w/ intake and ill put in $10 of gas, and at $3.75 per gallon of premium it gives me 2.660gal. and i will restart my odometer thing or w.e. and i wil get at most 35 miles before the gas light is completley on and the needle is on the E. And this is WITH coasting and shifting at 3-3.5RPM and 10 miles of highway eachday and the rest is city. Why is is so bad? and what can i do? if its coasting, i do it ALOT.



also i know there is a thread for bad gas mileage but i dont have enought time to read 45 pages of posts, im making a long highway trip and after that is ALOT of city driving on thursday and w/ schoola nd a job i dont have time to read all that....

[Oh, then by all means, go ahead and start another thread about a beaten-to-death topic for your convenience, and to hell with what we've been doing here for years. After all, you're the most important one of us all, princess.]

 

[Boost92awd]

Change plugs, wires, air filter, fuel filter, check tire pressure. Put a bottle of fuel system cleaner in the tank. Change PCV valve. Try to stay out of boost as much as possible. Next time you put gas in fill it up and drive to use some gas. Then fill it up again and see what your getting for MPG.

 

[DJYoshaBYD]

You drive a heavy turbcharged car.. What do you expect?

 

[bastarddsm]

drive it at 55-60 i'm getting 25-30, and my motor is wore out.

 

[rob1621]

so i have a bottle of seafoam in my garage....so do i put the whole thing in my gas tank...and then what?

 

[sniver]

yes. & then drive it till its nearly empty...

 

[talon187]

when was the last time you changed you 02 sensors? this may sound nuts but i know theres a thread on here somewhere i started. my gas milage went up after i installed my walbro 255 pump go figure

 

[the_mork]

Put it through your vacuum lines not your gas tank it will help in your gas tank but it will do more and do it more immediately through vacuum. Do a boost leak test this turned out to be the problem on my volvo 760 I had blown a small hole in one of my intercooler pipes. Do a tune up and don't drive over 70mph. With seafoam honestly I put one third in the crank case one third in the gas tank and one third through the manifold for general purposes and all through the manifold for fixing existing problems.

 

[PIMking]

I understand the mpg deal but its a sports car its not going to get prius mpg. Hell my tsi gets better mpg then the ole ladies volvo turbo and shes only fwd.

 

[steeda763]

If you're venting your BOV to the atmosphere try recirculating. I reverted mine from vent to recirc after reading some posts on the subject a month ago and noticed some gain in fuel economy.

 

[rob1621]

well i ran seafoam when i first got my car in january through the vac lines.

i dont know when the o2 sensor has been replaced (will that really help?)

i dont vent to the atmosphere

what is the easiest boost leak test to do?

 

[tunethis]

http://www.vfaq.com/mods/ICtester.htm

Once you fix any leaks (If you have any), you should save some gas.

 

[rock0134]

go to home depot and get an end cap piece of pvc that will fit in a coupler. Clamp that into the coupler and then drill a hole in it and put a valve stem in it. Put that on the turbo in place of the intake tube and then use an air compressor to put some pressure in it and listen for leaks or squirt soapy water on places where you think there could be a leak.

 

[turbo90gsx]

Pull off the intake pipe with the MAS sensor connected to it going to your turbo. Clamp on a boost leak tester on the turbocharger inlet and use compressed air or a bicycle pump to check for air leaks.

A slow (worn out) O2 sensor can drasticly effect fuel milage from keeping your car in a "rich" trim. You really only need to replaced the front O2 sensor as that is what your ECU uses for fuel compensations.

You can also try re-setting your ECU too. Disconnect the negative battery terminal for 10 minuets and reconnect. It may take a few days for the ECU to compensate its trims and IAC settings but you could see a difference.

 

[steeda763]

While you're down at the auto parts store buying an O2 sensor for 80 bucks, have them scan your OBDII port. They might find a code that a removed or blown check engine light bulb won't tell you about.

Here's a basic boost leak tester:

http://www.vfaq.com/mods/ICtester.html

 

[XilArAtiNG]

Having a working O2 sensor is VERY important if gas milage is in mind. Not to sounds like a prick but it seems like a few people always neglect the O2 sensor and rip it out saying "my car runs just fine". No it doesnt it goes into limp mode and most usually runs rich... O2 sensor is the ONLY way the car knows that it has the correct Air/Fuel ratio, and your LongTerm and ShortTerm fuel ratios are GREATLY effected by this. So verdict- make sure your O2 sensor(s) are working if your gas milage is suffering.

Fuel filter will go bad after 50k, I remember reading that question. Milage doesnt really matter on the fuel filter, if you buy very dirty gasoline at a gas station a few times, well theres a new fuel filter thats needed...

Clean your throttle bodies, and keep the damn RECIRC pipe on!! Yes it effects the car greatly (5 GAS TESTS) it will run lean and in order to correct that the PCM will send extra fuel and richen it up killing your gas milage. O2 see a rich signal, and it leans it out so your car is bouncing in a wide range of rich and lean in this state and using too much fuel to correct=bad gas milage.

 

[meliketoball]

You drive a heavy turbcharged car.. What do you expect?

My car is made of fiberglass. YES!!!

 

[ed1380]

i used to get 30+mpg mixed driving. now im getting more like 15.
new fuel filter didnt help
how do i check the o2 sensor or the TPS?

 

[1995gsx20g]

i was wondering because i am getting poor gas mileage overall and i would say 75% city and 25% highway and turned my boost controller down to bout 12psi and still get 14.5-15.5mpg and am getting a new exhaust in a few months that every aftermarket dp i see has no bung for an o2 sensor so what do i do then because i dont wanna spend the $120 for a new o2 sensor if im not even sure if its the problem and what happens to gas mileage when you get an aftermarket dp with no place for an o2 sensor? also how do i test the o2 sensor and the tps sensor?

 

[Ravenous]

I believe the rear O2 in a 2g is only there to verify a working catalytic converter, so it has no impact on gas mileage. Get a O2 simulator for it and you would be golden or fool tyhe ecu some other way so you don't get a cell.

 

[jared]

I just bought a 98 GS-T with 65k miles. I drove it home 500 miles and only averages about 23 mpg on freeway.

I am looking at ways to increase fuel economy. There are absolutely no aftermarket accessories.

looking at the following options:

air intake
I checked the spark plugs and they are autolites, not NGK
wires
new o2 sensors
fuel filter

what is going to be my best bet?

 

[pj91gsx]

if you free up the exhaust and eliminate the emissions then you can get better miles to the gallon. you can port match the exhaust manifold, port the turbo and the o2 housing and get a 3'' inch all the way back and eliminate the cat. porting is free so that is best if you dont want to spend money to save gas.

 

[kanderson]

23 mpg is actually pretty average, depending on how fast you were driving and how much of the time you were boosting. When I first got mine I was getting around 20 mpg : ) I'll attribute that mostly to my right foot, although I did find several vacuum leaks.

O2 sensor can make it run rich, as can vacuum or boost leaks, so check for those. You can probably make the biggest difference by changing your driving style though...

 

[DougR]

Get some form of Tuning device..
Now this Will increase Performance a small amount. But since you are seeking better Gas milage, you will beable to Lean your tune out a small amount and get better gas milage...

 

[pj91gsx]

boost leak test+1 and make sure you have the right spark plugs from ngk.