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

 

[winterftbl]

thats not true, a tuning device will help if you are not stock. But he is stock, so a tuning device will not help, especially on stock injectors.

 

[jared]

Iwas driving around 60-65 the entire way......all freeway. Edmunds states that freeway should be around 28 mpg.

I just pulled the plugs and they are pretty burned. could this be attributed to a bad o2 sensor?

 

[DougR]

What do injectors have anything to do with leaning out the mixture?!

A tuning device will let him do EXACTLY that.

 

[bluegs03]

thats not true, a tuning device will help if you are not stock. But he is stock, so a tuning device will not help, especially on stock injectors.

This is horribly untrue, a tune can help with anything no matter what car you have and no matter what mods you have. The ecu isnt tuned optimally from the factory they put it this way to reduce warranty claims and make sure nothing blows up when the car is stock. There is still horsepower and gas mileage to be gained from tuning the stock ecu. From what i remember i think the ecu runs slightly richer from the factory, by leaning it up not only will you gain horsepower but you will use less gas, because you are injecting slightly less gas per cylinder fire.

 

[GrnZ]

Our cars are indeed very rich from the factory. I installed my AEM UEGO and Safc2 on my pretty much stock 2g awd Talon, i took a ride with no tune and it was 10.0 (super rich) as soon as you get on the gas peddle at all. I put a pretty good tune in , leaned it out quite a bit and now it pulls harder and i get better gas mileage. Invest in a nice wideband and an safc or dsmlink, youll be very satisfied.

 

[dsm_Prince]

Dont waste your money on a safc. I had one but got robbed and now im saving up to get dsm link its way better.

 

[7"exhaust_tip]

Do everything on your "following options list" and add a boost leak test to it.

 

[DSM1G90]

...for as long as I keep my boost in the sane column, I can hit close to 30mpg with my stock Laser RS Turbo doing freeway speeds.

Hmmm: 65k miles - get your belt kits done for that might help also.

 

[2FoX2]

Going with OEM spec. NGK plugs is a good start.

Are you able to get some data through the OBD2 port to help see the benefits?
I have a vacuum gauge installed in my car and not only is a good tool for diagnosing engine difficulties, but it can help reform your driving habits if you monitor it and keep it as high as possible to maintain an optimal A/F

 

[selmerguy]

Let me let you guys in on a little something. Fuel economy really has not improved since the 70's. And in some cases gotten worse. This is on purpose. There was a deal struck between oil companies and auto manufactures. That production cars would only do so well on fuel. If you think about all the advancements in technology from the 70's to now it has to be the only logical conclusion. Have you tried lean burn. I have a 92 awd talon. Crusing at 14.7:1 AFR on the highway I get about 20 MPG. I took a road trip not to long ago cross country. I set my crusing afr's to about 16:1. 35 MPG and went all the way acrossed the country. I was very cautious with all my temps and got no knock. This was with 272 cams and all.

 

[Defiant]

Let me let you guys in on a little something. Fuel economy really has not improved since the 70's. And in some cases gotten worse. This is on purpose. There was a deal struck between oil companies and auto manufactures. That production cars would only do so well on fuel. If you think about all the advancements in technology from the 70's to now it has to be the only logical conclusion.

Oh, horse shit. None of the manufacturers will cooperate enough to gain anything. They're all only in it for themselves, not for each other. And against them all is the politicians and the special interests they're bribed to boost.
Turbo DSMs get less mileage than they could because they use extra gasoline as an engine -saving, combustion-chamber cooling method. Californians get even less mileage because we have shit for gasoline, a special California-only blend whose intent is to cut emissions. I'm still baffled how burning more can pollute less.

 

[selmerguy]

Oh, horse shit. None of the manufacturers will cooperate enough to gain anything. They're all only in it for themselves, not for each other. And against them all is the politicians and the special interests they're bribed to boost.
Turbo DSMs get less mileage than they could because they use extra gasoline as an engine -saving, combustion-chamber cooling method. Californians get even less mileage because we have shit for gasoline, a special California-only blend whose intent is to cut emissions. I'm still baffled how burning more can pollute less.

We will just have to agree to disagree. But my numbers are still the proof. If a 26 year old dude can figure out how to tune his car to make almost twice the mpg with no ill effects, (I dont know about environmental effects of this) then to think that a multi billion $ auto manufacturing company has to work with another to make the same thing is kinda silly. Dont they pay people lots of money to do R & D.

 

[fatherbubble]

23 is good when i got mine it got 15 or so a gal.

 

[clipse4u2c]

do your maintenance things. Check your tire pressure. plugs and wires. boost leak test. vacuum leak test. get a good intake and free flowing exhaust. I did that on a 94 ranger 4x4 with lift and went from 14.5 mpg to 19 highway!

 

[pj91gsx]

IMO gasmilage is mostly how you drive the car. being in the highest gear at 2000 rpms will save you more gas than anything else. also, intake and free flowing exhaust. I shift at about 2000 rpms instead of 3000, and save much more gas. If you keep the car at low rpms you will save more gas. my brothers car gets better gasmilage than me because he has a 6 speed and a bigger motor and I have a 5speed and a smaller motor.

 

[bastarddsm]

Mine gets 27, and its wore out. I have seen 30+ on my turbo conversion car with turbo pistons and no tuning device. Drive 60-65 and you will do better.

 

[cbrue122]

Looking at a completely stock vehicle your best bet for better gas mileage would be getting the new o2 sensors and a new set of NGK BPR6ES plugs. A bad o2 sensor can give false readings to the ECU, making the engine run rich.

Another possibility would be a bad coolant temperature sensor. If the ECU never knows when the engine reaches operating temperature it will keep fuel management in the "warm-up" mode and this can wreak havoc on mileage as well.

This has already been mentioned but it is worth repeating: driving style, especially with a turbocharged engine, has a lot to do with good and bad gas mileage. Install a good aftermarket boost gauge (autometer, etc.) and monitor it while you are driving. Try to keep it in the vacuum pressure range or at least very low boost pressures as much as possible.

I have done all these things with my 97 GST and can consistently get over 30 MPG on trips very similar to yours.

 

[Rx3]

STAY OUT OF BOOST!

MAke sure all the maintenance stuff is taken care of: O2 sensors (Very jmportant), coolant temp sensor, plugs, wires, clean air filter, fuel filter, check for all leaks (boost, vacuum), etc. etc.

 

[Defiant]

We will just have to agree to disagree.

Oh, here we go.

But my numbers are still the proof.

Your numbers are "proof" of what you came up with, in a few uncontrolled trials, at a given time. Genuine "proof" would be what your car got over its life, and what that life was.

If a 26 year old dude can figure out how to tune his car to make almost twice the mpg

While having one eye on the gauges, a careful, moderated foot on the throttle, and a keen ear on what the engine's doing all the time. How would you feel about your mother hopping into that car and driving it to Omaha and back? Are you confident that your knife-edge tuning would survive the trip with no damage to the engine? Could she haul it down the freeway with no idea of what it's doing, as most DSMs have spent most their lives?

with no ill effects,

That you've discovered so far.

(I dont know about environmental effects of this)

Nor do you have to consider them, as well as consider enough dither that every last car out of hundreds of thousands that you make will be able to be tossed onto a dyno every other year to have its emissions levels checked by a semi-simian who probably can't tell a Roots lobe from a Shorrock vane, as well as work under the threatening cloud of a multi-thousand unit vehicle recall program if you get a number wrong.

then to think that a multi billion $ auto manufacturing company has to work with another to make the same thing is kinda silly. Dont they pay people lots of money to do R & D.

They expend millions at it. Comparing what some of us could do in their own shops, with a certain example of an engine build and weeks to fiddle with it has no relation to what manufacturers have to deal with in order to make sure their product can drop out the end of the production line like so many road apples, and each able to pass various emission numbers which have naught to do with either performance or efficiency. Nor do many of us have a clot of mindless bureaucrats pulling numbers out of their asses and telling us to make sure we don't pump out any more hydrocarbons than X, and deciding to decrease that "because it's about time we wrote some other law".

 

[Rob10_99]

Wow D lett'tm have it!
About the only thing I agree with is the lean burn, PURELY at cruising speeds, 15-16:1 wont be too detrimental as long as there's egt's monitored as well as AFR's.
Anything with some decent load will smoke an engine quick with those AFR's.
Can't wait for his response to that.

 

[selmerguy]

I agree with you D. But I would let my wife drive it and do. In fact I am in Iraq right now and she drives the car a few times a week. And drives from San Antonio to Corpis and Houston alot. She has no problems and does no tuning. I have the car set up with 16:1 AFRs at lower percentages of throttle during crusing highway rpms. If she hit the throttle over about 36% it jumps to a different VE cell and the afrs are close to stock. So I have plenty of confidence in her driving it.

I dont like the emission laws anymore than the next car guy. But the people that created those laws were voted for. And that is what I defend.

I do agree with alot of the stuff you say. I like my economic car that will runn 11's before to long. Do your thing dude. I will do mine


Sam

 

[gsxeclipse97]

Well i can go about 270-280 miles before my gas light comes on. Also since my car if from California does that mean its also tuned to run richer like Defiant's even though i am able to use 93 octane?

 

[videogamemaster]

Alright so yes I do realize that hey a turbo'ed car is gonna cut into a 4 cyl. gas mileage greatly, BUT my gas mileage I just can't justify. It seems as if its only getting around 10mpg WTF

So I am asking all of you put down your list of possibilities that could be causing my horrifying gas mileage that way I can begin diagnosing each one

 

[webconnect]

boost leak, bad plugs, bad front o2 sensors...

 

[videogamemaster]

boost leak, bad plugs, bad front o2 sensors...

spark plugs were just replaced.
How do i go about doing a boost leak test?
How would I check the 02 sensors?