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Old 03-24-2009, 05:08 PM   #1
binkman88
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Unhappy mpg bad what to change?

hitting 82xxx 05 RS and have noticed bad mileage for a bit. I changed the plugs but not the wires and got about 75-100 more miles per fill up. What should be next? Im going to get wires for it but dont know where to get them autozone? advanced? This hopefully makes a big difference or else im out of ideas. Anyone else have any info?
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Old 03-24-2009, 05:21 PM   #2
jetfan2207
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-How are you calculating MPG? (miles per take is not very accurate. Fill up the tank, reset the trip, next time you get gas, fill it up and record the gallons you put in and the mileage on your trip, then divide)
-What numbers are you getting?
-I have 82K on my 01 OBS and get between in the mid to high 20s.
-Are you a lead foot?
-Tires all properly inflated? ( I run a pound or two over what the door jamb says)
-When was the last time the car was tuned up? (air filter, fuel filter, etc)

Last edited by jetfan2207; 03-24-2009 at 05:37 PM.
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Old 03-24-2009, 05:23 PM   #3
fastenova
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Not your usual 1997
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Fuel filter, air filter, check your tire pressure. Any check engine light?

Malfunctioning o2 sensors can sometimes cause poor mileage without throwing codes.

Winter gas is ethanol blend (10% or more in most states, to combat pollution) and will cause a decrease in mileage. I forget when it's usually changed, but a lot more states are running ethanol blends year-round, and without being tuned for it, it decreases mileage. The amount of power (specific something...?) in ethanol is lower than normal gasoline, so you have to burn more of the liquid to get the same power output. A lot of turbo guys who go to ethanol have to run substantially bigger injectors to get the same output.

Cold weather generally lowers mileage if you're making lots of short trips, as these cars run extremely rich when they're cold/warming up.

These cars are not econoboxes per se, AWD eats up some efficiency, as does an automatic transmission (not sure if you're 5MT or 4EAT).

Aaron

Last edited by fastenova; 03-24-2009 at 05:26 PM. Reason: punctuation rules!
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Old 03-24-2009, 05:41 PM   #4
binkman88
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im getting around 290 per fill up on regular. Im a lead foot here and there but whether i am or not I still get the same mileage. Fuel filter is in the tank on this car is it not? I might have to check that out and im running a aem intake and no CELS for me

5spd manual.
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Old 03-24-2009, 05:54 PM   #5
jetfan2207
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The fuel filter is not inside of the tank. It should be under the hood. I believe mine is to the right of the air filter if you are standing at the front of the car. 290 miles isn't THAT bad, that's over 18MPG if you are totally running the tank dry (assuming you have a 16gal. tank). But try calculating it the right way and see what you get.
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Old 03-24-2009, 06:35 PM   #6
iluvdrt
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clogged cats can kill MPG, and O2 sensors. 80xxx miles, it wouldnt be a bad idea to change the sensors. Coolant temp sensor too I have seen cause bad MPG's.
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Old 03-24-2009, 06:35 PM   #7
gunny11218
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the "correct way" is also the long way. It takes about a week depending on how much you drive but it will yeild a much more accurate answer. The wires are probably the next easiest thing to help get your Mpgs up there.

Not to thread jack, but is my fuel filter under he hood too?
98 legacy 2.5 gt
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Old 03-24-2009, 11:05 PM   #8
yarrgh
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yes, 98 legacy fuel filter is under hood, near driver side suspension tower. Get OEM wires from dealer or from Subie Gal, I forget the website. Have you been following regular maintenance? Mods?
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Old 03-25-2009, 01:39 AM   #9
Audi20Tdriver
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try calculating MPG vs mileage per fill up I think it is more accurate that way. Also, where are you located? there are 9 million things to affect gas millage. you have to average out your numbers over a longer period of time. It could simply be the gas you are using.. especially if it is a winter blend. On a side note, thats a ton of mileage on an 05. I just sold mine with about 42K.. are you up to date on your maintenance? Ever had the differential fluid changed? That could be a big one for MPG.
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Old 03-25-2009, 01:43 AM   #10
trueno16v
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Quote:
Originally Posted by binkman88 View Post
im getting around 290 per fill up on regular. Im a lead foot here and there but whether i am or not I still get the same mileage. Fuel filter is in the tank on this car is it not? I might have to check that out and im running a aem intake and no CELS for me

5spd manual.
Not sure about RS but in my 05 WRX, filter IS in the tank. I was told it doesn't need to be changed but I'm not sure. Dealer part only too.
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Old 03-25-2009, 10:53 AM   #11
eh1525
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Quote:
Originally Posted by jetfan2207 View Post
The fuel filter is not inside of the tank. It should be under the hood. I believe mine is to the right of the air filter if you are standing at the front of the car. 290 miles isn't THAT bad, that's over 18MPG if you are totally running the tank dry (assuming you have a 16gal. tank). But try calculating it the right way and see what you get.
Almost 100% it is in tank. I have been under my hood alot and have seen nothing that looks like a fuel filter.
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Old 03-25-2009, 04:01 PM   #12
binkman88
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yea im pretty sure its in the tank, but ill do wires, then go from there and let you guys know and how would I change the coolant temp gauge wheres it located?
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