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

 

[kawboy]

Dont forget 02 sensor. If its reading incorrectly, it will pump out too much fuel.

And how do you make it read correctly?

Only by purchasing a new one?

 

[The_EE]

If it was touched before it was put in, it can read incorrectly from what I understand. if your car burns a ton of oil that can foul out a o2. running really lean can do it too. Its possible that when you replaced it, you got a defective o2, I know I have. They are sensitive to shock.

 

[president95]

How many gallons are you fitting in your tank when you refill?

 

[rk4g63]

10-40 is kinda thick....I would suggest a synthetic 5-40 or 5-50

I use Mobil 1 10W30.

 

[wvturbo2]

do u run ## car hard ? along with one of these other problems maybe... u might total up to horrible gas mileage or is it just slow driving... i had a 3rd gen with the 2.4 and it was modded and i had been tuned for nitrous and ran rich... and it got bad gas mileage expecially since i ran it hard all the timeor is ## car stock

 

[Nautica985]

Actually the some Iridium plugs from NGK are pregapped. now other plugs are different, thats when you really need to make sure gap is right..

My NGK copper plugs always come gapped at .028

 

[toicy4ya]

Pooya: I’ve heard mixed opinions regarding using synthetic, but I don’t wanna open up a whole different can of worms on that subject. However, I don’t think there would be a big difference between using 10w-40 and 5w-40 or 10w-40 and 10w-30 for that matter, unless someone can prove me otherwise.

Kawboy: Someone on another forum brought up that point; I checked a site that compares the fuel consumption effect between stock wheels and aftermarket bigger wheels and the difference was something life .01. Not that much of a difference.

President 95: Good point, I will make a note of that today when I fuel up and take note exactly how many gallons were actually still in the tank if it doesn’t fill up to 15 gallons.

Wvturbo2: I don’t run my car hard at all. That definitely wouldn’t be the problem here. The high cost of car insurance and tickets in New York has me driving like a B*tch.

 

[jari8378]

I was running rich for some time, i think it was due to a boost leak i had near my stock smic, i not a "wiseman" but i would check my vacum lines for boost leaks

 

[boostdog]

i bet your wheels have alot to do with it...on my daily drive (02 neon) i swapped the 14"ers out for some chrome 17" wheels .... slightly bigger diameter and alot heavier...i get about 6-8 miles less to the gallon...right around 19-20. for winter i swapped the stockers back on and now i get 25-28. put the stock wheels back on and see if that helps.

 

[DSM90AWD]

Actually the some Iridium plugs from NGK are pregapped. now other plugs are different, thats when you really need to make sure gap is right..

My NGK copper plugs always come gapped at .028

NGK Lists >700 applications that uses the BPR6ES plug each having it's own recommended gap. They may set a target gap during manufacture that unmolested (e.g. not dropped, roughly handled) may end up being within your car's gap tolerance. But why chance it?

NGK's recommended gap for the 1Gs is .032 (Mitsu says .028-.032) and I've found variances within that range and +/- over the 16 years I've owned the car. To blindly install plugs without first checking the gap to 1.) ensure consistancy btw plugs and 2.) to ensure it falls within the recommended gap is just not smart.

Also note that preignition (knock) can open/close gaps and damage the electrode or the insulating sheath. Running too cold a plug may also diminish fuel efficinecy as plugs are designed to operate at a certain temp to self-clean

 

[kawboy]

If his wheels are considerably heavier than stock, they will most definetly affect gas mileage, being as they are already oversized

 

[ilikespeeding]

I was running rich for some time, i think it was due to a boost leak i had near my stock smic, i not a "wiseman" but i would check my vacum lines for boost leaks

Its a N/T

 

[DGajre777]

Its a N/T

I have the same problem, I get 180 miles for 11 gallons of fuel - that's about 16MPG. I have done a complete tune up + fuel filter, but haven't changed the o2 sensor yet. Hopefully when I turn my boost down, I'll get better gas mileage cause I'm running super rich (muffler is all black).

 

[president95]

President 95: Good point, I will make a note of that today when I fuel up and take note exactly how many gallons were actually still in the tank if it doesn’t fill up to 15 gallons

Don't we have a 16.9 gallon tank?

 

[slugsgomoo]

sounds like you should start tracking your actual economy, rather than guessing with the fuel gauge (which is "accurate", only to an extent).

Fill the car, reset the trip meter. Drive until the light comes on. Fill it up, take the number of miles driven, divide by the number of gallons put in, voila, instant mileage.

I doubt your wheels are causing that much issue unless they weigh an insane amount more than your stock wheels, or they are the wrong size (in terms of diameter) and that is throwing you off. If your odometer was off by 10%, you could be reporting 220 miles and going 200, or visa-versa.

I'd start with that, make sure your gaps are proper on the plugs, double check your air pressure, and keep an eye on your driving style.

I'd almost consider getting an alignment as well, especially if the car is lowered, and hasn't had one. Excessive toe can drastically reduce fuel economy. You can check for it with a measuring tape (you'll need a friend)- Measure the distance from the center point of the right & left tires on the backside, and on the front side. If the distance on the front side is less, you are toe in, if the distance on the rear is less, you're toe out. Either can adversely affect economy (and tire life)

 

[Nautica985]

Don't we have a 16.9 gallon tank?

15.9

 

[toicy4ya]

sounds like you should start tracking your actual economy, rather than guessing with the fuel gauge (which is "accurate", only to an extent).

Fill the car, reset the trip meter. Drive until the light comes on. Fill it up, take the number of miles driven, divide by the number of gallons put in, voila, instant mileage.

I doubt your wheels are causing that much issue unless they weigh an insane amount more than your stock wheels, or they are the wrong size (in terms of diameter) and that is throwing you off. If your odometer was off by 10%, you could be reporting 220 miles and going 200, or visa-versa.

I'd start with that, make sure your gaps are proper on the plugs, double check your air pressure, and keep an eye on your driving style.

I'd almost consider getting an alignment as well, especially if the car is lowered, and hasn't had one. Excessive toe can drastically reduce fuel economy. You can check for it with a measuring tape (you'll need a friend)- Measure the distance from the center point of the right & left tires on the backside, and on the front side. If the distance on the front side is less, you are toe in, if the distance on the rear is less, you're toe out. Either can adversely affect economy (and tire life)

I tested that recently, Yesterday my gas light went on, I proceeded to drive for another 30 miles with the light on. I go to fuel up my car today (sunoco regular unleaded) and it filled up with 13 gallons of gas, I guess it still had a little over 2 gallons of gas left. My odometer read 230miles since I last filled the tank. I guess that means I drove 230 miles on 13 gallons of gas which I think would equal to roughly 18mpg city.

I heard our gas gauges can read our gas tank incorrectly at times. I guess my next question would be, Is there anyway I can fix the gas light so that it lights when there's only 2 gallons left in the tank (as noted in our car manuals) as oppose to 4-5 gallons?

I will be checking my plugs to make sure they're gapped corrently. I also got a wheel alignment about 2 months ago.

 

[DGajre777]

I drove 200 miles on 12 gallons and my gas light never went on, my fuel gauge was on E. The gas light is a idiot light, it is not that accurate any way.

 

[president95]

15.9

Just checked my owners manual.......... 16.9

 

[1993eclipseGS]

You're complaining about 200 miles to a full tank? Wow, What are most people getting then? I remember when I was happy to get 100 on a FULL to the gas cap of 94 octane... I was seeing 70-80 miles to a full tank. Oh well, I never had good gas milage with ANY car I had though.

 

[DSM90AWD]

I get 2+ months on a tank of fuel

For the original poster, do you have any exhaust leaks and/or is it possible your catcon is clogged?

 

[DGajre777]

You're complaining about 200 miles to a full tank? Wow, What are most people getting then? I remember when I was happy to get 100 on a FULL to the gas cap of 94 octane... I was seeing 70-80 miles to a full tank. Oh well, I never had good gas milage with ANY car I had though.

Oh no, I'm not complaining about 200 miles on a full tank, but when I see people coming in here and saying they get 300-350 miles on a full tank in their AWD car, it makes me wonder why I get shitty mileage. And no, I don't drive slow, I'm at WOT in every gear, every day.

 

[b-nizzzle]

Today i had to fill up my tank..I got 230 miles for 13 gallons thats like 17.6 mpg My car is 97 Gst stock, i drive the speed limit like 90% of the time, i dont rev it up alot.. could anyone help me out and tell me what gas mileage they get and what the problem could be.

 

[jccjr1982]

Depending on my weekly moods(how I drive):

Normal: 250 miles from full to empty mark

Aggressive: Anywhere between 200-230 from full to empty mark


Right now I'm at only 170 miles and I'm less than an 1/8th of a tank... this is gonna be the worst one yet... but I've encounter alot more stop-n-go traffic recently since my work schedule changed.

I'm not the smoothest and most consistent shifter though...



On my N/T auto, over the course of 3 years it dropped from 320 miles per tank to 250 per tank... I noticed it dropped when I started disabling OD and doing "L" launches....

 

[Eclipse98Spyder]

check your fuel filter may help a good 7%