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

 

[Defiant]

It will take a couple of weeks for your ECU to re-adjust itself to your new setup. Give it the miles to do it, it should get back to normal shortly.

 

[james13]

so when i switch it back wait a couple weeks and everything should be better?

after a couple weeks and the mileage is still crap then what do i do?


-james

 

[n0va91TSI]

Wow can my 91 ECU do that or is it a 2nd gen feature only?

 

[Bd1000Eclipse]

Originally posted by Defiant
It will take a couple of weeks for your ECU to re-adjust itself to your new setup. Give it the miles to do it, it should get back to normal shortly.

what? did i read that right?

 

[ITSME4G63]

THERE IS NO FIX, I LOVE MY 7MPG

 

[n0va91TSI]

defiant knows his stuff

but im thinking it may be a second gen thing

 

[Defiant]

Originally posted by james13
so when i switch it back wait a couple weeks and everything should be better?

If the cause of your low mileage lies in your venting -which your ECU had been trying to compensate for- then a return to normal should help.

after a couple weeks and the mileage is still crap then what do i do?

Less boosting, more coasting.

 

[4geze63]

I vent with no problems

 

[Spyke169]

Originally posted by james13
so when i switch it back wait a couple weeks and everything should be better?

after a couple weeks and the mileage is still crap then what do i do?


-james

either turn the boost up more and stop caring about gas mileage... or buy a honda

 

[Zenja]

Umm, venting wouldn't really affect milage from running rich between shifts.

To vent properly you need to position the MAS after the BOV. This is usually done with a GM MAS and a translator and putting it in the UICP.

 

[Bd1000Eclipse]

Originally posted by Zenja
Umm, venting wouldn't really affect milage from running rich between shifts.

ahh yes it would...

 

[james13]

Like i said guys i am switching my setup to greddy so everything should work better

either turn the boost up more and stop caring about gas mileage... or buy a honda

might be easy for you to say but my pockets must not be as deep as yours....i can't afford $1.75 a gallon and get 120 miles to a tank



-james

 

[Stanford]

Is your car in good running order? If not this will also affect gas mileage. Don't blame it all on your blow off valve, it could be many other things. One of the biggest factors is also how you drive your car, like Defiant said less boosting and more coasting.

 

[timmy]

make sure you change your plugs and wires after swithcing the bov. You prob fowled the plugs.

 

[herostar]

stop venting

also, my bad o2 sensors made me get about 11 mpg

 

[james13]

so did both of your sensors go bad?

anywhere cheaper than autozone that has them?
at autozone the sensors are $70 a piece

also what plugs and wires should i replace with?


-james

 

[Factor]

I have been running rich since i got my Apexi BOV, i have been reserching it and i found that there is a screw on the bottom of the MAS that you can adjust the air intake. I plan on opening mine up a little (since its all the way in) and letting more air in to compinsate for the air lost due to the venting i will do this mod tomarrow and i will post and tell you if it help fix the problem. i know you are just running rich on shifts but if you lean it out a little it might help. Here is a link where i found this. http://www.roadraceengineering.com/eclipsetech/2gmasadjustment.htm

 

[Factor]

Ok i opened it up all the way and i took out the bottom honey comb. when my blow off vents im not running as rich as i was and i still have a good mixture when i drive. All and all i would say take the bottom honey comb out and screw that screw out and you should see an improvement.

 

[TTalon]

hey guys,
i just installed my exhaust cutout yesterday and i fille up ultra 94 yesterday and i have only gone about 80 kms and its already close to half tank!!!!!!!!! thats BS!! i duno whats wrong or what is causing that? i cleaned the injectors,fuel filter,emissions removal, wires,plugs,air intake,TB cleaner...i duno what is causing it to use so much gas...perhaps a bad o2 sensor? can someone help please!! thanks

 

[Flash]

I know what you mean. I useto go through a tank of gas each week, just driving to school and back 3 miles each way for 5 days out of the week. I later found out I was driving to hard. Since then I've slowed down and I'm making a tank of gas last me 3-4 weeks. It sucks not feel boost, but what ever it takes to save gas. Try it.

 

[TTalon]

damn i havent even turned the boost up yet...and it guzzles this much gas...thas insane!!! ultra 94 is 90 cents a litre here too!! ill wait for some more posts but ur right takin it easy does save up some gas for sure ...lez see what others have to say ...
thanks

 

[SpeedFreak03]

A bad O2 sensor would cause a rich condition. Does your car ever bog, do you have any black soot in your tailpipe, and how does it idle? Running rich can reduce gas mileage quite a bit. Did you start noticing this right after installing the cutout tho?

 

[TTalon]

Originally posted by SpeedFreak03
A bad O2 sensor would cause a rich condition. Does your car ever bog, do you have any black soot in your tailpipe, and how does it idle? Running rich can reduce gas mileage quite a bit. Did you start noticing this right after installing the cutout tho?

well perhaps i should take a look at a new o2 sensor? any recomendations? and yeah there is a lot of black carbon/soot build up in my tailpipe and in my piping near the downpipe.... its idles messed up too sometimes 1rpm sometimes lower sometimes 1200...ive been trying to fix it but i managed to make it 1rpm for the most part...
well this problem was ongoing but i have seen imprvements then before since i changed many parts and did a lot of maintenance and still i should be seeing 400km a tank at least and i barely make 300kms....

 

[TTalon]

anyone?

 

[KeltonDSMer]

The only thing I can think of would be to get a wideband O2 to see what is going on; that's kind of pricy though....