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

 

[AnkurJ0217]

It may be a boost leak. I repaired my boost leak and drastically improved my mpg. I was doin 12 miles per gallon. Now I'm up around 15-18 mpg.

 

[Hybucci]

Sorry for the long post.

Ok tried searching and came up with a few things but still wondering. I had some boost leaks before and i figured that instead of spending 200 to have them fixed I would get a FMIC Kit. It was a cheap ebay intercooler with some non-dsm prebent pipes. It was all pieced together perfectly running the short route as i have seen done by others on the site. So I get it out of the shop and think, sweet its going to fix my fuel consumption problems. It didnt. To make a long storie short im getting about 200 or less off a full tank(15 gallons).

Driving Style:
When people say that they get good mileage with out boosting does that mean not all the time or 10 psi for about 10 seconds every 50 miles? I usually drive to were I boost at about 1-2 psi through 3rd gear to get up to speed.

Also while it was in the shop, I had the mechanic put in a new boost controller but it didnt controll the boost until he adjusted the wastegate to about 10psi(moderately low because I dont want to blow it up in the winter cold). He said that he talked to some of his buddies and they all said that I would have to get a new wastegate but he runs cummins turbo diesels at the track and he adjusted the wastegate like the diesels and it sits right around 10 psi.

Sorry for another boring post and thanks for the help.

 

[larsrya8]

What do your fuel trims look like?

 

[spyderturbo007]

Have you replaced your front O2 sensor since you've had the car? As larsrya8 asked, do you have a logger? Are you getting a CEL?

Also, you don't need a new wastegate.....Well, you might, but I seriously doubt that's the problem. I would say that you need a new MBC. It sounds like the spring in your current wastegate isn't strong enough to increase the boost over stock settings. Where did you get the MBC?

 

[Megamanx]

I get horrible gas mileage. I mean 250km to the tank. Its really bad. The exhaust smells very rich. I have no idea whats going on here. My friend said that my injectors might not be atomizing the fuel very well. Also when I'm driving and I have it floored (well almost) sometimes randomly the engine will almost cut out for a second. I'm not sure if this is related to the fuel system or not, but just throwing it out there incase.

 

[jking29]

Is your car completely stock? The first place I would start, would be to do a boost leak test. A boost leak will cause the car to run excessively rich and would cause you to hit fuel cut which is what it sounds like you are describing when you say the car cuts out.

 

[luv2rallye]

Also check your O2 sensor and coolant temp sensor. If not working it usually runs rich.

 

[djjohns55]

It could be your EGR valve if its not those other things mentioned in previous posts.

 

[Megamanx]

Hello all. I have a 1990 Eagle Talon TSI AWD. Right now my car currently gets 250km to the tank. Yes the TANK. It's rediculous. My friend suggested that the injectors might not be atomizing properly, but I don't know if he has any experience with these cars. Also, when I'm driving and I have it almost floored(I dont do this anymore), almost most definately the engine will like stutter, or cut out. It's really weird. One friend suggested that it could be the fuel system, another said it could be my engine misfiring. I have no idea. Does anyone know whats going on here, and how major this problem is?

edit: Also the exhaust smells pretty bad. Very rich

 

[FORMONTOYA]

The sputtering sounds like a boost leak (or any number of things, but with the info provided.......), The O2 sensor could be trash, the injectors could be clogged, etc.

More info is needed other than "I have bad gas mileage, what's wrong?".

 

[Megamanx]

Its not like sputtering, it's more like the engine cuts out for a split second, then return to normal. What other kind of info do you need?

 

[251Eclipse]

that definately sounds like your injectors. mine did that when i first got my car so i took them out and put in some new ones.

 

[Megamanx]

How much for new injectors roughly? CDN.

 

[VTRICCO]

you can start by only starting one thread about the SAME topic
http://www.dsmtuners.com/forums/showthread.php?t=252306

 

[Megamanx]

Sorry I never knew that thread was even created, when I made it my internet cut out probably 3 seconds later.

 

[c5chris]

edit: Also the exhaust smells pretty bad. Very rich

Your O2 sensor must be fouled, making your fuel:air ratio rich which contributes to your low mileage.

 

[siceclipse]

look, its a 17 year old car.

change the spark plugs, wires, fuel filter, both front and rear O2 sensors, and test/check your fuel pump

replace all of these and do a boost leak check.

 

[shaunman1979]

look, its a 17 year old car.

change the spark plugs, wires, fuel filter, both front and rear O2 sensors, and test/check your fuel pump

replace all of these and do a boost leak check.

I second that! But in a 1g your only going to have one O2 sensor up front none in the rear. Read the faq and get yourself familiar with your car. These are great cars they just need alot of love. Good luck

 

[DSMLaser90]

what are you running for octane, just the basic maintence will do you fine
also check the integrity of the sendin-unit

 

[DSMnOOb00]

WTF So i just got this bitchen new 97 GSX, all stock and still a virgin! but i notice that my gas mileage was a little low, at first it thought that maybe AWD just takes a bit more then FWD but then i filled her up 91, and zeroed out my counter thingy.... im at 190 ish and at below 1/4 of a tank... that means i get like 220 pre tank?! is that right? what could couse this?WTF

 

[absolute_DSM]

Check for boost leaks.

Change oil, air filter, and fuel filter.

Welcome to DSMs.

 

[dsmdreamin]

new car + joy riding new car(heavy right foot)= poor mpg

congrats on the new buy

happy dsming

 

[Talesin]

Check your front O2 sensor, for one.
For two, GSX have a shorter gear ratio (by a LOT), including fifth. So even if you're just cruising, you're not going to be getting that great mileage... my old GS-T would cruise at 65 around 2Krpm. My GSX hits 65 at 3000.

Cruising at double the RPMs is going to eat gas roughly twice as fast, under the same throttle/airflow, so the same applies to time and a half.
Best I've ever gotten on one tank in the GSX is 330 miles, and that was drafting off a big rig down from the bay area the whole way (14 gallon fill at the end).
250 miles, full to empty of around-town driving is not out of the question. 200 or less with a heavy foot is to be expected.

Still tempted to buy a GS-T again, just to use as a DD.

 

[Rob10_99]

On my 90 GSX I got anywhere from 150-300, 300 being the absolute most grandma driving possible.
and the 150 was GOOOOOO!!!!!
14b mostly stock btw

 

[B-lackGSX99]

I was shocked at my fuel economy also, I think the best i've ever done was 250, and that involved a lot of highway driving. Here in the city, i'm lucky if I get 200. I'm glad to hear others are having the same issue in their relatively stock GSX's...this way, I know my mods aren't really affecting my fuel economy as much as I thought!