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

 

[larsenracing]

i get about 23 in town running it pretty hard and about 27 highway. mods listed

 

[Defiant]

We have many mileage threads.
When figuring mileage, do it ONLY in MILES PER GALLON.

 

[Matrixhunter]

I can't seem to figure it out the car runs great but the fuel consumption seems to be beyond normal. Maintenance wise everything on the car has been done lately oil/ fluids etc.

I also added a metal intercooler piping but i dont think that could cause it?

Could the air/fuel ratio be off somehow and if it is can it be adjusted i'm also thinking it might be the o2 sensor but i guess it must be working fine because otherwise the car runs great. Any opinions/ suggestions would be great thanks.

 

[andymoraitis]

I think you're on the right track with the front O2 sensor since it controls all non-WOT functions. A good idea would be to stop by a local AutoZone and see if they can pull up any trouble codes. If you have any post them here and we'll help you figure out a solution if it's not evident.

Another thing to pay attention to is the coolant temp sensor. If this is malfunctioning, it will always tell the ECU that water temps are not where they should be and burn considerably more fuel as a result (richens when cold). To answer your question regarding A/F ratios, these are calibrated into the ECU and cannot be changed except by using a chipped EPROM ECU, AFC, standalone, DSM Link or through adjusting fuel pressure.

Let us know what you find and we'll do what we can to help,

Andy

 

[Mist3r Spool]

Well, what kind of mpg or miles/tank are you getting? Is your CEL on? Do you drive it like ya stole it ? Is this a new problem that happened after you installed the hard pipes? You do get better/more accurate boost w/hard pipes and you may just have a heavy foot (like myself) after installing something that gives you some more kick. I get ~370/tank with 91-octane, when my primary o2 went bad (common, apparently) I was getting around 290 or less. I don't know what kind of auto stores you have in your area but hopefully you'll be able to follow the advice of andymoraitis and get your ECU scanned for trouble codes. When your car is running rich (due to a bad o2 for example) you may actually notice an increase in performance. Just FYI.

 

[reNgrOets19]

now if ## o2 sensor is bad will the check engine light be on mines not on but i get horrible gas mileage seems like when i don't get on it at all i get worse gas mileage...thanks guys

 

[BoostActionBob]

same thing happened to my car and it wasnt timed right. you may want to check that. check spark plugs. wires. air filter. replace/clean. and while your at it clean out the throttle body with some intake manifold cleaner and also clean the maf. thats what i do when i tune her up.

 

[Matrixhunter]

Thanks for the replies as for gas mileage i was getting around 380 to a tank now i would it say that im not getting more than 250 260. About a month ago my timing belt almost snapped the balance shaft belt broke and the car died on the highway as a result the timing went off 3 teeth but no internal damage luckily. I had that fixed at the shop but i remember when i opened the hood on the highway the manifold and the turbo were molten red like if fire was going through the manifold so i'm thinking the exccesive heat might have burned the o2 sensor or damaged it because the car still runs. I'll have it checked today and will let you know.

Any suggestions on what type of o2 sensor to buy bosch?

 

[BoostActionBob]

go bosch all the way.

 

[Mist3r Spool]

Thanks for the replies as for gas mileage i was getting around 380 to a tank now i would it say that im not getting more than 250 260. About a month ago my timing belt almost snapped the balance shaft belt broke and the car died on the highway as a result the timing went off 3 teeth but no internal damage luckily. I had that fixed at the shop but i remember when i opened the hood on the highway the manifold and the turbo were molten red like if fire was going through the manifold so i'm thinking the exccesive heat might have burned the o2 sensor or damaged it because the car still runs. I'll have it checked today and will let you know.

Any suggestions on what type of o2 sensor to buy bosch?

As for the o2 sensor, go w/stock parts-how long did your previous sensor last? I wouldn't take a Bosch sensor if it was free, they're Kragen crap. I'm not trying to knock BoostActionBob, but I've seen nothing but bad results with Bosch o2 Sensors in a DSM. The only thing I purchase thats Bosch is winshield wiper blades, period. You can find OEM o2 sensors on-line for under $100/new.

 

[BoostActionBob]

no offense taken but i have put bosch in all my vehicles my 95 TSi and my 91 TSi and they have done extremly well. maby i'm just lukcy. or you could go with a wideband o2 kit that would be bad ass

 

[HellsSephiroth]

wow your gas mileage isn't really that bad, in town i probably get around 5-10 mpg. it seems like. A simple 20 mile trip costs me $10.

 

[VAGRNT]

yeah i was getting about that until i fixed a boost leak i had, then i got an extra 100 miles out of a full tank of gas, but now it smells like i have the leak again.

 

[95DsmTsiauto]

Thanks for the replies as for gas mileage i was getting around 380 to a tank now i would it say that im not getting more than 250 260.

Wow... I wish i had a fwd as a daily driver. My tsi gets 150-230 around town because of my SUPER SMALL t25 and its need to spool at such a low rpm. A kid who lives by me has a bigger turbo and it spools at a higher rpm and his gas milage is like 320-350 because when he drives he doesn't need to spool unless he is getting on it.

 

[Mist3r Spool]

Wow... I wish i had a fwd as a daily driver. My tsi gets 150-230 around town because of my SUPER SMALL t25 and its need to spool at such a low rpm. A kid who lives by me has a bigger turbo and it spools at a higher rpm and his gas milage is like 320-350 because when he drives he doesn't need to spool unless he is getting on it.

Interesting...I get the same gas mileage on my 16G as I did on my T25, probably because they have similar spooling characteristics.

 

[Mist3r Spool]

no offense taken but i have put bosch in all my vehicles my 95 TSi and my 91 TSi and they have done extremly well. maby i'm just lukcy. or you could go with a wideband o2 kit that would be bad ass

Oh, yeah, I need a wideband myself.

 

[95DsmTsiauto]

Interesting...I get the same gas mileage on my 16G as I did on my T25, probably because they have similar spooling characteristics.

well I know practically nothing about turbo sizes but the guy who lives by me has a 60-1? i believe and his car spools at like 3600. So he can drive around all day and keep it under 3k but with my car i would like to drive at 3k but my car spools because my turbo starts to spool at 2200. So i cant..

 

[Mist3r Spool]

well I know practically nothing about turbo sizes but the guy who lives by me has a 60-1? i believe and his car spools at like 3600. So he can drive around all day and keep it under 3k but with my car i would like to drive at 3k but my car spools because my turbo starts to spool at 2200. So i cant..

It also depends on how much throttle you're giving it-if you have a heavy foot, your turbo will tend to spool sooner.

 

[ddavisaf]

So where are we at with this....?

 

[BoostActionBob]

i agree. hows the gas mileage/ tune up. whats the story with this.

 

[birdii]

I just got done doing some general maintenance to my car, the basics: changing my fuel filter (which took me forever since the bolts were really rusted and PB blaster wasn't even working on them!), air filter to a K&N, new plugs/wires, tranny fluid and oil change, checked tire pressure.. the works for a tune up but I'm still getting real poor gas mileage - been using lucas injector cleaner too. I can get approx 200 miles on a tank. No check engine light or anything, i'm thinking an injector but not sure... any ideas?

i got the same problem after my tuneup..... i was getting around 300miles on a full tank but now its around 200 .....is it possible if an o2 senser is almost dead theres no engine light comes on or codes show up when you scan it...?

 

[DSMTC03]

I would think it is a faulty O2 sensor. I get 375+ miles per tank on my 97 420a non-turbo.

 

[blcknspo0ln]

i second the o2 assumption...

btw, i get 300 mi to the tank ON boost

 

[MyBeatGSX]

Here's a weird idea. What if your gas gauge is off. According to my gauge I get about 220-240 miles until its dead on E. But when I go to fill up it only takes 10 gals. I don't like going by mileage per tank fill, whats your mpg? I average around 20-22mpg and I drive like an old lady 95% of the time.

 

[BoostActionBob]

you may also want to check timing on the vehicle. mine had a problem with that and it was a little off timing. also while you were doing the tune up did you clean anything. if not you may want to take the throttle body off and clean it with some intake manifold cleaner. clean the tps and isc. throw the throttle body back on. get a new can of it and spray it in it opening and closing the throttle. use half the can for this. then start the car. it may have some problems running but just plug the throttle body with your hand a little bit while spraying with the throttle open. use the rest of the can on this. put everything back together. while you have the mas off clean that also. might as well its all apart anyways. once everything is together and you start your car it may smoke. don't worry its not bad. i keep good gas mileage records. and after doing this it jumped mabe 4 to 5 mpg. oh ya and make sure your spark plugs are gapped right. .028 to .030. what kind of spark plugs are you using. might want to look into ngk bpr6es. Good luck

edit: o2 sensor is a wise check also.