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

 

[Talesin]

Front O2 sensor going bad is the usual biggest problem. The fuel filter is a good design and rarely clogs (good thing too as it's a bi*** to replace). I'd grab an ODBII scanner from Autozone and let the car idle. Watch the O2 value... it should fluctuate up and down. If it's solid at a given number, or is giving no reading, it's bad.

Generally the biggest giveaway is when a DSM is only giving around 14mpg, or abruptly went WAY down in fuel economy. 95% of the time it's a dead front O2 sensor.

 

[b-nizzzle]

ya im going to do a boost leak test first then change the fuel filter then ill see what happens hopefull its not the o2 sensor.

 

[president95]

Read thru some of these. Mainly the one right under your thread

http://www.dsmtuners.com/forums/search.php?searchid=1913851

 

[blackGSX2g]

I agree with Talesin. Check your front o2. When I first got my car, the sensor went bad I was getting about the same MPG you are. I bought MAFT and a new o2 sensor and it bumped into the low 20s. I've now been able to get 300 miles of moderate boost driving out of one city driven tank.

 

[carl5463729]

I have a 90 gsx, i used to get 17mpg also will driving slow. i just put on a 3 inch turbo back exhuast. and guess what i went up to about 23mpg. i don't know if this will be the same for you but i'm guessing my catalytic converter was clogged beyond belief. I still can't believe the difference since it is a bigger exhaust. i don't know when cat's go bad but that is another possibility. Just to let ya know i did change the air filter, fuel filter, plugs, plug wires, compression test (150 all across) and a boost leak test before the exahust and none of it helped. good luck

 

[Slow4G64]

Air Filter is worth a look too, if it's full of dust then it will beahrd to suck air in. Probably not as big a problem in a turbo car, it's still worth a look.

 

[b-nizzzle]

like 3-4 weeks ago i get new timing belt and balance shaft belt and spark plugs and oil changed..im probably going to get a new air filter and fuel then see what happens first.
thanks for all your help

 

[jibberishballr]

02 Sensor

 

[sniver]

Wow I just did a 380 mile trip and only used like 8.5 gal of gas...thats like 45 mpg.. I love my n/a for the economy ...though I usually manage 32 mpg

 

[jibberishballr]

difference between front sensor and jsut a plain 02 sensor is? And if there two separate would both need replace if gettin bad gas mileage?

 

[president95]

There are two 02 sensors

 

[blackGSX2g]

Only the front sensor relates to your fuel mileage, the rear is only to monitor the cats efficiency. Shouldn't cost you more than like $60.

 

[nismo4life]

be lucky your getting that much. When the Talon is done I expect 9-11mpg. Are you launching at all? My friend in his 91 TSi likes to launch off the line and spin through 4th and then he asks why his gas milage sucks. Also try a basic tune up.

 

[blackGSX2g]

be lucky your getting that much. When the Talon is done I expect 9-11mpg. Are you launching at all? My friend in his 91 TSi likes to launch off the line and spin through 4th and then he asks why his gas milage sucks. Also try a basic tune up.

I don't even think my gas mileage is that low on track days.

1. boost leak test
2. o2 sensor
3. tune your car to get your fuel trims in spec

 

[b-nizzzle]

hey guys could anyone help me.. im trying to find posts on changing front o2 sensor but i can't find any, is it difficult?

 

[IslanderTsi]

no it isint per see. ou have to remove you're upper/lower turbo heat shield. Which gives you acess to the 02 sensor. It has wires running from it to a clip that you unplug on the left side of the engine.

You need to get a 02 sensor socket a very strong ratche/wrench and more than likely a breaker bar as they are generally a pita to break loose. Also using a torch to heat the bung up wouldent be a bad idea. Dont worry about frying the wires as you are replacing them anyways.

 

[VicBoost]

Only the front sensor relates to your fuel mileage, the rear is only to monitor the cats efficiency. Shouldn't cost you more than like $60.

Where can i get one and where is a good place to get a walk through to install it. My gas mileage isn't that bad, on $20 of gas i get about 150km. So thats about 20Litres and i get 150 km.

 

[zippyshoe]

You may be able to borrow an o2 sensor socket from your local Autozone for free. That is what I did when I replaced my faulty o2 sensor. This is one of those specialty tools that you will probably not use very often, so it may make more sense for you to borrow this tool than to purchase one.

 

[b-nizzzle]

You can get a Front o2 Sensor at Sparkplugs.com for like 50$ plus shipping.

Ill try asking them if they will let me borrow their o2 sensor socket, wouldnt hurt to ask, thanks!

 

[-TunedDSM-]

Quick questions why does my gas light thing come up when i still have 1/4 tank left. Does it just warn you earlier or is it just my car that does that. WTF

That is normal, its just letting you know that you are getting low on gas and that you should get more. My friends 95 TSi AWD does the same thing. It doesnt happen in my GSX for some reason though. I think the bulb is just burnt out for the light. My car is the same with MPG. I did a test and i get 16 MPG driving it nice, shifting around 3k.

 

[GinNBoost]

Quick questions why does my gas light thing come up when i still have 1/4 tank left. Does it just warn you earlier or is it just my car that does that. WTF

My car's gas light comes on when I reach just below the 1/4 tank mark too. Then it'll go away and won't come back on til I'm dead near E. I thought I had a faulty signal, but if yours does that too then I guess it's normal.

 

[president95]

How many gallons are you guys fitting in your tanks? We have a 16.9 gallon tank, but I can only fit about 13 gallons at the most when the light has been on for over 70 miles, and the stupid gauge is all the way to the bottom. Maybe some of you are getting better mileage than you think, you just arent calculating it correctly.

 

[VPrime]

I think my gauge is wayy off..
I normally fill the car up at the 1/4 mark and almost never let it get to the E, and the pump tells me that i am filling 30-35 Liters (7.9- 9.24 gallon)... so if its a 63 liter (16.9 gallon) tank.... that means my gauge is off by a lot.... because technically that would roughly be the half way mark wouldnt it?

I once let it get to the E (well a little above) and the gas light came on, then faded away... if that means any thing
Im to scared to actually run all the way empty to see where the gauge stops at compared to the car....

 

[president95]

My gas light plays the blinking game too, and eventually it will just stay on, and I always wuss out. These gauges are shit. My gauge is always as low as it can possibly go, with that yellowish light giving me visiual tension for over 50 miles, and I still cant fit over 13 gallons in there. Im currently getting 22mpg, so Im NOT refilling until I get 320 miles out of this tank (15 gallons). Screw that ####in light.........The gauge too

 

[KGB Pilot125]

on a 1G the light comes on when you have 2.1 gallons left in the 16 gallon tank. I currenty get about 310 miles out of a tank. I have only filled up twice since I bought the car. first tank 25 second tank 24 but that included 11 miles of WOT rally driving