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

 

[blacklabel5281]

You say just tune your car. What exactly do I need to tune my car? DSMlink?

 

[95TalonOwner]

Definately one of the first thinks you need to do is boost leak test! Don't waste 500+ bucks on dsmlink if you want it just for better gas mileage.

Also, put your BOV recirculation tube back on! You will run like crap since you will be running rich as hell which in turn gives you worse gas mileage.

Also, your cat might be clogged and if that's the case, then you might need a new one. One time on my 91 Laser RS turbo I had a clogged cat and when i got rid of it I got 50 more miles to the tank.

 

[TheNewGuy98]

ok.. i have a 98 gst, ive have it for about 5 months and recently ive only been getting about 200 miles to a tank. i have new plugs and wires and intake and filter from turbo up. i changed my tranny oil about a week ago and that seemed to make it get even worse. will mileage go down if i put to much oil in? i change my motor oil ever 2500 to 3000 miles and use castrol syntec 10w 40(i live in florida)also the engine seems to rattal alot at idle but the the idle itself is smooth.. when i first got the car i was getting close to 400 miles to a tank, now im only getting half(if im lucky)......please help

 

[Ultimatedsm]

Replace your front o2 sensor, it should of been part of your tune up. The o2 sensor doesn't necessarily put a trouble code all the time. Is your car stock or what kind of mods have you done so far?

 

[98gst14b]

How many miles are on your car and have you done any mods to it since you got it? A long shot but it may be about time for your cat converter to clog up......

 

[MyBeatGSX]

No one measures gas mileage in miles/tank. These gauges are extremely inaccurate. It could be indicating E and you actually have a 1/3 tank left. I usually have 1/4 tank or more left when its on E.

But even so, 400 miles/tank is outrageous. No one gets that. I average 20mpg driving around my parents house (more steady cruising) and 17-18mpg around my house (lots of stop/go). Either way I drive like a grandma. If I drove it hard it would be <15mpg.

It usually comes out to 200-215 miles before each refill, and I refill at 1/4-1/8

 

[AsILayDying]

Yea, I could believe 400 mpg out of a N/A, since that's about what I could get out of my old Eclipse, but not a turbo. I agree with mybeatgsx. The gauges are very inaccurate, especially if you make a hard run. I've had it drop an 1/8 of a tank and then when I turn it off for a while and get back in, it's back where it was.

 

[TheNewGuy98]

No one measures gas mileage in miles/tank. These gauges are extremely inaccurate. It could be indicating E and you actually have a 1/3 tank left. I usually have 1/4 tank or more left when its on E.

But even so, 400 miles/tank is outrageous. No one gets that. I average 20mpg driving around my parents house (more steady cruising) and 17-18mpg around my house (lots of stop/go). Either way I drive like a grandma. If I drove it hard it would be <15mpg.

It usually comes out to 200-215 miles before each refill, and I refill at 1/4-1/8

__________________________________________________________________________


i have no mods exsept for what ive listed, intake and plugs and wires..
my fule gauge i farly accurate because i fill it up as much as posibble and drive it till the light comes on and i always can put about 12 gal. in at the pump, and yes when i first got the car i could get around 380 miles till the light came on

 

[TheNewGuy98]

i noticed the bigest decrese in gas milage after i changed the tranny oil, thats why i wanted to know if adding too much could do anything?

 

[Jetblack]

No possible way! I'm not hating I'm just saying, there's no way unless you coast 50% of the time go pedal .e. Alot of it depends on your driving style. I went from 15mpg on 1 tank to 20mpg the very next with no changes except forcing myself to lighten up on the gas. It was by no means fun driving but I had to prove to myself that it wasn't the car and this is with 660 injectors, big fuel pump and all the other crap that makes the car fuel inefficient. So change that O2 and see what happens and lighten up on the go pedal

 

[TheNewGuy98]

thats just the thing.. this isnt just a one time thing for the first 2-3 months i had the car it was getting great gas mileage and i was always going somewere so i was constantly driving.. but for the past month or 2 my mileage has almost been cut in half i dont drive the car any harder than i did when i got it.. i actualy drove the car harder when i first got it but now ive had my fun and got my share of tickets and i dont really drive it as hard as i used to.. i dont know everything but i would say i know alot about cars.. just not how to fix all the problems.. i could tear the engine apart and put it back together with no problem but i just dont know what i would have to replace to fix my problem..sry if i sound like an ass im not trying to be..

 

[dsmclipse97]

yea def replace that front 02 sensor... my gas mileage was cut in half when mine went. dont worry about the rear 02... its worthless performance wise

 

[bhop]

But even so, 400 miles/tank is outrageous. No one gets that

Not necessarily. I have gotten 400miles/tank or close to it on road trips on several occasions, meaning mostly freeway driving with steady traffic, cruising in 5th gear. But since most people don't drive mostly freeway traffic, I don't consider that 'normal'. General every day traffic driving in l.a. gets me around 250/tank.

 

[TheNewGuy98]

ok thanks ill get the o2 replaced asap(any special brand name i should get?).. and as far as adding to much tranny oil that wont make any difference right?..

 

[jdhutchin]

It's hard to add too much transmission oil on a manual, just pull out the filler bolt and let it drain until no more comes out- then you have the right amount. If you pull the filler bolt and nothing comes out, you're fine there. And I wouldn't think that'd have much of an impact on fuel economy anyways.

 

[TheNewGuy98]

ok. i didnt think it would make a difference but just wanted to make sure. and theres one more problem i maving.. i dont know it its just normal for these cars or whatever, i hear about other people having the same problem... after my car warms up it makes a knocking/ticking noise but only wile at a dead stop. is it that have bad oil pressure or something?

 

[spcrxracer]

After reading ALL 29 pages of this thread, I was surprised I didnt see more data.

Here are some ACTUAL numbers, starting since I've owned my car. I keep a log in a small notebook and I record everything, and I note when maintenece was performed.

I took the time to put my data into Excel.

Please keep in mind that:
-I fill up AT or a little below 1/4 tank (w/91 octane).
-I shift at 2.5-3k RPM (96% of the time).
-My foot is NOT lead.
-All data is for 55% Hwy, 45% city (unless otherwise noted).
-Car is UNMODIFIED.

Here's the chart:

You must be logged in to view this image or video.

 

[blacklabel5281]

Well I want dsmlink for the power increase as well. Not just for better gas mileage. Two I trying to find a tube so I can re-circulate the bov. Lastly I run a downpipe. No cat here for me. haha
I'm looking to replace my Ram Air filter. Mine is looking a little beat up. Right now I have the Apexi Power Intake. Would I get more power if I buy a hard pipe from Injen? Like do the full Injen setup?

 

[DGajre777]

I used to get 150, after a fuel filter change it jumped up to 200. The next thing on my list is my front o2 sensor.

It is important to gap your plugs. You have to gap them to 0.028". NGK BPR 6ES are pre-gapped to 0.035". You might want to look at this too - http://www.dsmtuners.com/forums/showthread.php?t=239375

If you plan to keep your BOV, you will need to get a GM MAF and MAFT setup, which means if you get an Injen intake made for the 2G MAS you will have to end up selling it. www.dejonpowerhouse.com makes good intake pipes.

 

[blacklabel5281]

I was looking into the GM MAF and MAFT setup. What do you know about it? Where does the sensor go? It will allow me to vent the good way correct? I was also told it needed to be tuned or something and that with the weather changing it would mess it up or something.

 

[DGajre777]

I was looking into the GM MAF and MAFT setup. What do you know about it? Where does the sensor go? It will allow me to vent the good way correct? I was also told it needed to be tuned or something and that with the weather changing it would mess it up or something.

Inorder to vent it correctly you will have to place the sensor in the upper intercooler pipe AFTER the Bov. Read this - http://www.dsmtuners.com/forums/showthread.php?t=174055

 

[Wherestheboost]

I do have a check engine light on which I tried getting tested with other scanners. However they were unable to recognize the codes and said that I should try to bring it to the dealer and get it diagnosed there. As far as the soot in the rear bumper I don't think I have that and the spark plugs were changed not too long ago. Thanks for the input and I will most likely get it diagnosed first to see what is wrong and post it.

Like stated in above posts, o2 cel's cause hooorrrible gas mileage as well, to my knowledge and experience, egr problems that may or may not cause a cel. As well as, also stated in above posts, simple things as making sure the air filter is clean, spark plugs, fuel filter, and a simple induction service may serve as appropriate measures to help with the pummeling MPG.

 

[Blue95GST]

i get almost 300 per tank, so about 22 per gallon, and i drive a lil over what you call "normal driving"

 

[ericmetcalf11]

Do a "key dance" and it will tell you what your codes are:
http://www.2gnt.com/nuke/modules.php?name=Sections&op=viewarticle&artid=8

 

[Jason2215]

I was just curious, what is "BG Products?" Sorry...a little behind on the lingo, but sounds like something I might want to do.