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

 

[ChicksDigBoost]

Bad plugs and wires, Fuel filter, air filter, clogged injectors, bad O2 sensor, vaccuum leak, etc etc

 

[JST2FST]

You may also want to make sure you don't have any leaks in your fuel tank.

 

[Import_Chic98]

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?

 

[Game Over]

Check all the vacuum lines and sensor plugs, could be an o2 sensor. I get about 200 miles to the tank, but that's pretty good for me.

 

[TSiWarrior]

Check the o2, mine just died and im getting close to 5 miles to the gallon.

 

[99GSXAWDTURBO]

I have a stock 99 gsx with the exception of a apexi n1 catback exhaust system and im only getting 180-200 miles per full tank of gas. while ive heard other people getting upwards of 300 miles a tank. Ive replaced the spark plugs, and got a new air filter which helped some. Could changing my fuel filter help, what about my 02 sensor? could that be doing it if its bad? what else could be casuing this?

 

[MaddMatt17]

It could be several things, but the o2 sensor could be it, cause it would be sending wrong msgs to the ecu. Usually if its an o2 the CEL will come on..

 

[RUSURE]

I have a 95 Eagle Talon AWD Turbo and I've got some minor problems with the gas mileage as well. I go through almost a quarter of the tank a day and I don't drive much at all. If I were you, and this is what I plan on doing too is changing the fuel filter and spark plugs. If the fuel filter is original, definitely change it.

 

[Spoolin4Ever]

I get about 250 per tank in combo heavy commuting city traffic and some highway.

I think I could only get 300 per tank on all highway driving.

Remember driving hard and boosting alot will make it worse.

 

[bane3d]

How many gallons does it take to fill yours up? I know I'm new to this but from what I see, the mitsubishi holds about 16.9 gallons. I know mine shows that I've gone through 10 gallons when I have less than a quarter tank. Are you sure that you aren't estimating? I thought some people changed their gauges so that they would show an accurate amount left. Is it possible you are getting about 200 miles for 10 gallons when you have only used only about a little over half?

 

[tstkl]

yea, my gauge reads empty when ive gone through 10 gallons... while the stock 1g has a 16 gallon tank.... so i normally get like 300 miles per 13-14 gallons tho, cuz i drove my car really slow and conservative... but now that ive started modding it, and got the car painted, i dont think ill be driving it at all... just use my sisters car while shes at college... and mine for the occational weekend cruz....god save my dsm.... and he did

 

[99GSXAWDTURBO]

It could be several things, but the o2 sensor could be it, cause it would be sending wrong msgs to the ecu. Usually if its an o2 the CEL will come on..

is the CEL a warning light in the gauge cluster? Ive changed plugs, my new change is going to be a new OEM fuel filter...I realize boosting accounts for some of it, but i experimented, one a completly full to the top tank of gas, i got 190-200 miles when the low fuel light came on...this from boosting very little at all and driving very conservitively

 

[bhop]

is the CEL a warning light in the gauge cluster? Ive changed plugs, my new change is going to be a new OEM fuel filter...I realize boosting accounts for some of it, but i experimented, one a completly full to the top tank of gas, i got 190-200 miles when the low fuel light came on...this from boosting very little at all and driving very conservitively

CEL=Check Engine Light

FWIW, I get about 180-200 miles on a full tank in constant stop and go traffic, this is with hardly any freeway miles. (work commute). On the freeway only, I get closer to 400 (based on a recent road trip)

 

[99GSXAWDTURBO]

ah....im a dumbass it has been on for a few days, but my bad gas mileage had been occuring long before it came on. What about the inaccurate gauge reading? i havent heard about this...how can i alter my gauge so it will read accurately?

 

[MaddMatt17]

I think dsm.org used to have how to alter your gauge.. i dont know if they still do or not. Might be something in Vfaq. About the CEL just go to like a local autozone and they scan it. Last time i had mine scanned they said it was fuel trim cut due to a faulty o2 or defective mass... but you really never know with a dsm. Its not always the fuel filter either, i changed mine (it was a pain too for me) but i blew through my old one and it wasnt clogged at all, but it never hurts to get new ones filters dont cost much at all.

 

[EclipseGsxDsm]

I just brought a 91 gsx backt to near driving condition, well everything is fine now, but the car burns gas really bad and the exhaust is blowing black smoke. Im not burning oil, but it is guzzleing gas. Im guessing it is a boost leak or maybe a bad injector. Im just wanting some other ideas on what could be wrong. Input is very much appriciated!

 

[speedy13]

does it sputter at a light?or hesitate then shoots like a rocket? My guess from what you describe would be a bad O2 sensor,but as a first buy,buy a logger and it will be your best friend in these situations.

 

[DSM BEEYACH]

I just brought a 91 gsx backt to near driving condition, well everything is fine now, but the car burns gas really bad and the exhaust is blowing black smoke. Im not burning oil, but it is guzzleing gas. Im guessing it is a boost leak or maybe a bad injector. Im just wanting some other ideas on what could be wrong. Input is very much appriciated!

Are you getting a CEL. IF so you may have a bad O2 sensor.

 

[ltvarney]

A bad o2 won't always throw a code. Happened to me. My A/F gauge would only work part of the time. It was wired up fine so I got a new o2 and that fixed my problem.

For yours to just be blowing black smoke like that, it sounds like it would be something else or a combination of things. It's possible you have a stuck open injector that is just dumping fuel. It's also possible the exhaust valve(s) have a problem and are thus letting unburnt fuel past them.

So either you've got too much fuel in the cylinders, or the exhaust valve(s) are shot. You can check the valves easy with a leakdown tester. You should be able to rent one from an autoparts store. You bring the piston to TDC and apply compressed air to the cylinder. If you lose pressure, feel the tailpipe for leaking air. If you search, you'll find more info on the leakdown test.

Once you rule out the valves, you can be confident it's a bolt-on affair and can begin troubleshooting the fuel path (injectors, fpr, etc.)

 

[Shadow1189]

Recently since I bought my car I noticed that it really is bad on gas, and this week when I filled it completely I only get 185 miles per full tank and that seems to me like something is really wrong with it because the tank it 15 gallons, but really only takes about 13-14 gallons and my car is supposed to be 19 gallons on city mileage. Those numbers would indicate about only 9.7 gallons in but I am getting angry cause I have to fill up alot. Is there any parts I can buy to increase efficiency throughout my fuel system?

Thanks, Art

 

[92awddsm]

Check and/or replace the o2 sensor. That is the most common cause for poor gas milage. You shoud also check/replace coolant temp sensor, air filter, plugs, wires, cat, boost leaks, fuel filter, and all your vacuum lines.

 

[BoostActionBob]

i noticed my talon was doing the same thing and i did some looking and it had jumped timing. so i threw on a new timing belt and tensioner and retimed it and i'm back to around 22 mpg.

 

[Sotarts]

Is your car completely stock?

If I don't push my Talon, I will get 20+mpg/city. I like to push it, so I get anywhere from 10mpg to 13mpg (stock turbo, 18psi with 510cc's and HP 255 lph fuel pump). If I get on the highway, even pushing it, I get over 25mpg.

 

[BoostActionBob]

same here.... i get about 28 mpg on the highway pushing it a lil bit.

 

[Mist3r Spool]

Mods are in profile, I get 350mi-375mi to the tank on 91-octane from 76.