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

 

[Woody91GSX]

Along with checking the gaps, which is a slim chance, I'd try the O2 sensors. Can you get a pocketlogger or something to check them? Run a bottle of injector cleaner, check the air filter. See what that does. Hopefully, you can get back to mid 20's in MPG.

 

[my95tsi]

I did disconnect my 2nd O2 sensor from the exhaust and wrapped it in aluminum foil and hung it under the car somewhere so my check engine light didn't go on. Could that be the problem too? But i heard the 2nd o2 sensor doesn't mean anything and only checks to see if you have a cat.

 

[my95tsi]

Originally posted by TSiAWD666
Change your gap to .028". Verify that your O2 sensors are functioning, most importanly the first one. Check the grounding straps on your exhaust. Look for intake and exhaust leaks.

Now that i think of it there was a grounding strap attached to the cat when i removed it. But i got rid of it completely b/c i couldn't get it off the cat.

 

[Woody91GSX]

Grounding strap won't do anything really. It can get it's ground from the engine.

 

[stuffy1256]

i dont know whats wrong! im getting around 8-9 mpg with my cutout installed. i do run it open so is that what is killing my gas mileage? help anyone!

 

[allwheelTSI]

i don't think that has anything to do with the cutout.. are you sure its that low? i've seen 500hp rat motors get better gas mileage than that..

 

[Defiant]

"Cutout" from where? Do you mean you have your BOV vented to atmosphere?

A "cutout" refers to an exhaust adapter that bypasses the muffler system.

 

[stuffy1256]

yes i resently got a cutout before my cat....if i do a first gear pull i can literally see my guage moving....

 

[MiNiONTSI]

you should actually get better gas milage w/ a less restrictive exhaust.

 

[jb talons]

Originally posted by MiNiONTSI
you should actually get better gas milage w/ a less restrictive exhaust.

Not necessarily. The more air you move = the more power you make = the more gas you use. If you free up the exhaust, your car needs to deliver more fuel to keep up with the air flow.

However, I would also expect something else to be wrong for that poor of gas milage.

 

[MiNiONTSI]

actually if you make more power then you can use less throttle therefore getting the same gas milage. If all factors remain the same and the exhaust path becomes less restrictive then you will get better gas milage, the engine doesn't have to work as hard pusing the exhaust gas out. With a turbocharged car you really don't move that much air part throttle when off boost anyways.

 

[Knuckles2.0]

maybe its cause with the cut out open you have a led foot? i hope ya dont just cruise around the parking lot sounding like ya lost your exhaust on a speed bump..... dont be that guy.....

 

[stuffy1256]

i drive like i always drive...i never go above 3k rpms....how can i tell if im running too rich? coulld that be the problem? and also my o2 sensor was going out before i got it...i thought that if i got the cutout then the o2 sensor would be a factor...would this be causing the bad gas mileage?

 

[Knuckles2.0]

a bad sensor could definatly make you loose gas mileage but i dont think it would be that great a difrence.......

 

[jb talons]

Originally posted by MiNiONTSI
actually if you make more power then you can use less throttle therefore getting the same gas milage. If all factors remain the same and the exhaust path becomes less restrictive then you will get better gas milage, the engine doesn't have to work as hard pusing the exhaust gas out. With a turbocharged car you really don't move that much air part throttle when off boost anyways.

OK every car should drop their exhaust and end the world's gas dependancy problems. It's obvious if you use less throttle you'll use less gas, but who puts on a cut out for the sole purpose of using less trottle. The engine has to work the same just to get the air through the turbo. The turbo is the most restrictive part of the exhaust.

...if i do a first gear pull i can literally see my guage moving......i never go above 3k rpms....

c'mon
Not trying to give you a hard time stuffy. My gas milage is greatly affected the actions of my right foot. If I had a cut out, it would greatly change the weight of the right foot. A bad O2 sensor can cause a problem also. If it's not sending a signal the car thinks it's running way lean and tries to compensate by richening the mixture.

 

[MiNiONTSI]

If you drop your exhaust you will get better gas milage, you are also releasing very harmful gasses into the atmosphere. That's why we have emissions, they weren't desgined for performance.

 

[Knuckles2.0]

Well let’s bash every one now............ any way... how is the car idling? Have you had any resent work done on your car? I had an exhaust welded on my old wheels and it fried the ecu and it was running in "emergency mode" the whole time, I guess you have to disconnect the battery or some thing ....I’m sure some one knows what I am talking about any ways it was running incredibly rich you could probable light the exhaust.... does it smell like its running rich?

 

[stuffy1256]

i capped the cutout today and the car is running a lot better. i guess the 02 sensor was thinking it was too lean and trying to over compensate. my teacher told me about this device that sends an electric signal that you can buy that tricks the sensor into thinking the mixture is perfect.

 

[theTuner]

"my teacher told me about this device that sends an electric signal that you can buy that tricks the sensor into thinking the mixture is perfect."

i think you just learned what a basic piggyback is

 

[stuffy1256]

thats what a piggyback is? i never knew. hahaha

 

[eclipse90gs]

hey guys i just swapped a 6 bolt block with 2g head and front cover on my 95 gst. i bought the car with crankwalk so me and my dad did the right thing and swapped the 6 bolt in it. i upgraded a lot on it soo far. but the only thing i upgraded with the fuel is a walbro 255 fuel pump. my gas mileage sucks and i have no clue y? if anyone can help me plz do! i would appreciate it. thanx.

 

[JDubb]

fuel regulator? smell any gas? fuel filter? many many things...my 95 rs is not the greatest on fuel mileage and i don't know why either

 

[92redman]

Some sort of restriction? Dirty air filter? Could be a lot of things, how bad is your gas mileage?

 

[Enigma_Man]

If you only have a Walbro 255, and nothing else fuel related, that's probably a lot of the problem right there. The Walbro moves more fuel than the fuel pressure regulator can deal with, and your fuel pressure can't drop down low enough at idle / high vacuum cruising. So, you're squirting in more fuel. The solution to this is to get a good aftermarket fuel pressure regulator.

Other simple things that might be causing this are: Bad O2 sensor (watch the voltage level, it should cycle up and down at about 2x per second or so at idle), Intake leak (make an intake leak tester for about $3 per the vfaq), bad spark plugs/wires, dragging brakes.

-Jesse

 

[JDubb]

yeah i don't know anything about that particular fuel pump but thats why i figured you might need a fuel pressure regulator for the simple fact that the pump might be puttin to much fuel to your combustion chambers