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

 

[speedracer91]

sorta...i'm also a lil low on doe so... :thumbdown

 

[96TSi_Chris]

Id bet its an o2 sensor. Its about 100 bucks and then 60 bucks labor if you cant do it yourself.

 

[Smoothie97]

18 mpg in the city for me! Stock injectors with a Walbro 255 pump. That is with a new O2 sensor too. :thumbdown

 

[96TSi_Chris]

18 mpg in the city for me! Stock injectors with a Walbro 255 pump. That is with a new O2 sensor too. :thumbdown

And thats bad why?

 

[2gGSX]

see this thread http://www.dsmtuners.com/forums/showthread.php?t=124669
things to look for:
exhaust leak
plugs, wires
O2 sensor
TIRE PRESSURE this is really important
also, if you're putting in low octane fuel this will hurt your mileage

 

[speedracer91]

that may be it i only put in 87? octane right now...i only work 2-4 days a week for $5.75 an hour...ya it sux w/o money also what is the stok tire pressure supposed to be?

 

[Aikouka]

see this thread http://www.dsmtuners.com/forums/showthread.php?t=124669
things to look for:
exhaust leak
plugs, wires
O2 sensor
TIRE PRESSURE this is really important
also, if you're putting in low octane fuel this will hurt your mileage

Stock pressure is 32/29 (front/rear), but I've always read that this isn't very good, so what is a better pressure for better gas mileage? Right now I'm getting 26mpg, and I'd like to raise it a bit.

 

[speedracer91]

i've got 32 ish ?

 

[boostaddictgsx]

My last tank went by in a week, i got 230 miles off of 13 gallons, so thats about 17.7mpg, now, I'm mostly cruising, not a lot of stop and go, and according to the stock boost gauge, I'm not boosting any more than 3psi. I think I have a bad O2 sensor, and I have a boost leak out of my turbo, i think that is causing it, any other ideas?

The ideal situation would be to get a new turbo, manifold and O2 housing with O2 sensor, but thats not going to happen anytime soon. at 27 bucks a tank for 93 oct, the money I could be saving goes to gas.

 

[speedracer91]

How do u know u have a leak?

 

[2gGSX]

speedracer91 - If its before the cat, you'll definately know (this will KILL your mileage) by the annoying loud noises, and if its after the cat/o2 sensor (like mine) it will be a deeper louder note, and still not sound normal. Even with my leak though I'm getting 23mpg on average mostly local driving.

boostaddictgsx - Go through the checklist again, but if it's really an O2 sensor you should really replace that as soon as you can, since it would really help your mileage. Other than that try cleaning your injectors, either with a fuel addative or manually taking them out. Finally check your tire pressures.

As for tire pressures, I just inflated mine to recommended specs based on the tires (the guy I bought the car from put on different tires), and these recommended 36-38ish, but not over 40. I just drove the car to the gas station after work (30 miles highway round trip) and filled them up to 38 psi. I'll reopen this thread and tell you how much of a difference this actually makes, but either way check what pressures your tires recommend.

Finally, look over your driving style. I usually drop to neutral on downhills then revmatch when I have to go back up.

 

[Defiant]

i have a 91 Talon TSi awd w/ an a/t it seem to use a lot of gas..like so bad that my dads lincoln ls V8 gets better mileage is something wrong is there a secret to better mileage?

What IS your mileage? 20-22 is about average for the GSX.

And no, there is no "workaround" for broken car parts

Next, slow down. More than any of the other little "tricks", not pushing so hard against the atmosphere will give you the greatest gain.

 

[psychlow]

Next, slow down. More than any of the other little "tricks", not pushing so hard against the atmosphere will give you the greatest gain.

Aside from that, keeping your boost level down will further increase your MPG, and keeping the throttle level down will improve it further.

The engine control unit (ECU, the car's computer) is set to try to achieve a safe air/fuel ratio given certain input variables, which include airflow (how much air is entering the engine) and TPS% (throttle position sensor, or how far you're pressing down the gas pedal).

When you increase throttle position quickly (snap the throttle open) or are at sustained high TPS percentage positions (floored), the ECU will inject more fuel and decrease timing advance to be safe in case you increase engine RPM quickly by flooring it. This saves the engine by staving off detonation or preigntion of the fuel mixture, but results in poor gas mileage whether or not you actually floor it.

Likewise, it's programmed to provide a richer A/F ratio when you ingest a large amount of air, such as when the turbo is boosting. Forced induction cars like about a 12-12.5:1 A/F ratio under boost (and it's really safe from the factory, I've read more like 10.5:1 stock) but only require 13-14:1 or higher (depending on engine load) under vacuum.

 

[speedracer91]

hmmm well u did n't need to tell me what an ECU was cuz i'll be paying for my new one till i die...and i actuallly have the sticker for my car (the dealership one) :laugh: and it says 20 mpg but i caould go like 30 miles and lose a lot of gas....it bugs me...sorry about the ecu thing it was not meant to be mean

 

[psychlow]

No worries, just noticed your sig.

How much did you pay for the ECU?

 

[asexton6969]

To the guy who said his stock boost gauge said 3 psi..... Dont ever look at the stock boost gauge it is no where near telling u the actually boost. You cant even turn your boost down to 3 psi. Get an aftermarket boost gauge. Then you will know how much boost you are running.

 

[Defiant]

hmmm well u did n't need to tell me what an ECU was cuz i'll be paying for my new one till i die...and i actuallly have the sticker for my car (the dealership one) :laugh: and it says 20 mpg but i caould go like 30 miles and lose a lot of gas....it bugs me...sorry about the ecu thing it was not meant to be mean

Fill the tank, set the tripmeter to 0, drive a week, fill the tank and tell us how many miles and how many gallons.

I suspect you're running fine, and are being misled by the inaccuracies of the DSM fuel gauge.

 

[speedracer91]

psychlow- i payed like $300 ish to have it sent out and be fixed...the junk yard wanted $250 and it might have not even worked! i'll get some money and let u guys know how many miles i get just to let u know it may take a while for the $

 

[psychlow]

That's not that bad. You could've probably found a working unit for half that on DSMTrader (as long as you watch out for the scammers, that is) but a rebuilt one is better in the end anyway.

 

[2gGSX]

just an update, i think im looking at about 240-250 on this tank
which is about a 6-8% increase, from fully inflating my tire pressures




that and i've been driving all highway lately

 

[speedracer91]

Thanx for the help guys!

 

[nurseryboy]

Hey guys,

I am having a problem with my 96 Talon AWD. When I am driving it and give it gas to the point where the turbo kicks in, the car really boggs down. Actually, it runs ok up to around 3 psi, and then from 4 to 8 psi or so it doesn't seem to make any power (boggs down), and any more than 9 psi, the car starts bucking like crazy. If I leave off the gas, the boost goes down, and the car runs fine. At normal idle, I am getting about -20 psi.

I was told by a local mechanic that it was the BCS. So, I got a MBC to bypass it. I installed it today, and it seems to have helped the problem a little, but there is still a major problem. The car also seems to be running pretty rich now as well.

Do you guys have any ideas on what could be happening? Is there anything I can check to see if it is not functioning properly that would cause this? The mechanic is stumped.

Thanks,

Matt

 

[Rick4g63]

Sounds like a boost leak. Do the following below:

- Check all clamps and hoses from the intake to the throttle body. make sure the clamps are properly secured.

- Check all vacuum lines especially the one going to the MBC, the line coming from the turbo and the bov vacuum line.


Keep us updated.

 

[ivanr4g63]

yeah... a boost leak indeed, try this to make a leak test on your intake path...
http://www.vfaq.com/mods/ICtester.html

 

[nurseryboy]

Ok. It is pretty dark outside so I cannot check right now. But I do remember something I noticed when I removed the intake today to work on the MBC. I have an aftermarket intake, and it has a hose that connects it to the turbo inlet (thank goodness!). On one side of the hose it is bulging pretty good. I believe it is OK, but I will double-check it tomorrow. If it is not completely sealing, could this cause a such a problem?

I had done a boost-leak test about a week ago (when the problem started), but I couldn't find any leaks. But, I only had the stock boost gauge (now I have an aftermarket one) so I couldn't see what boost it was holding. What happens when you reach a certain pressure while doing that? Will the BOV go off, or where does the pressure go? When I did it before, I had the air compressor on it for a good minute, and nothing at all happened.

Thanks,

Matt