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Old 12-09-2002, 07:17 PM   #1
imprezey
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2001 2.5RS Coupe
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Default Poor gas mileage from GC8

my car gets terrible gas mileage. its a MY01 RS that gets a terrible 18 mpg/city. i don't stomp on the gas pedal too much so i doubt it is that. i run 91 octane because i have a proECM, i'm guessin that this is at fault here. i posted about this before but never really got a clear response. i know that with the proECM you need to run higher octance (91) but that the gas mileage should become better, or so i've heard. my other mods include: ganzflow, stromung midpipe, and stromung dual tip. does anyone have a suggestion for me besides taking the proECM out? i was thinking maybe getting Apex'i S-AFC to see if im running rich or something but i'm not quite sure of this route.
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Old 12-09-2002, 07:40 PM   #2
munkis
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your rs is only rated for a peak 21 mpg in the city, 28 highway, assuming your 5spd.

auto is 23 city 28 highway

Jay McDade
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Old 12-09-2002, 07:54 PM   #3
doobie
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I get 18 to 22 on a consistant basis, I also rev to 5500 on a consistant basis. Your 18 mpg doesnt sound that far off.
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Old 12-09-2002, 10:18 PM   #4
imprezey
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oh. damn. thanks for the help
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Old 12-09-2002, 11:07 PM   #5
stew
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one quick and easy thing you could do to see if your running rich is to pull a spark plug and see how its lookin. that might give you some idea.
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Old 12-09-2002, 11:48 PM   #6
imprezey
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what would it look like? really burnt or something?
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Old 12-10-2002, 01:45 AM   #7
SubyBean
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ya the plug will look almost burnt or have some type of black soot on it if your running rich, or if your really lean they will have some sort of glossy effect to it almost like they are polised on the ends
Brian
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Old 12-10-2002, 02:22 AM   #8
jeddy
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This exact thing happened to me right after i replaced my spark plugs. Yes, one was loose. Not enough to affect the idle, or make it run poorly, but just enough to not get full compression under load i guess. It ran rich rich rich, and i got 18-20 mpg (i usually get 24 or so, even w/ autocrosses in there).

I checked all the plugs, made sure they were all tight, and the mileage is back around 24/25 again.
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Old 12-10-2002, 03:55 AM   #9
RugDoc2003
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it seems as if our cars are quite sensitive...

i too have a proECM and in the city i'll get 18mpg too... but that is the dead city... around my parents home (suburbs) i get about 22-25

on the high way (after a bit of HW driving) i've got up to 30mpg

so the proECM did help... but not in the city

you may be ok

rug
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Old 12-10-2002, 10:39 AM   #10
Julian
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I get 30mph for highway driving, no PROECM, no 91 octane. I've never done a full city tank, so no factual mileage on that.

But 18 doesn't sound far off for full city. 91 octane is also less efficient in burning, so you can see a reduction in mpg there as well.

"I don't stomp on the gas pedal too much..."
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Old 12-19-2002, 08:19 PM   #11
imprezey
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Quote:
Originally posted by McDade
your rs is only rated for a peak 21 mpg in the city, 28 highway, assuming your 5spd.

auto is 23 city 28 highway

Jay McDade
haven't manuals always gotten better mileage then autos? and most people on the board get 22-26 mpg, or so i've seen.
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Old 12-20-2002, 09:37 AM   #12
BrysImpreza
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I have the 2.2 liter and I'm not getting much better mileage about 20 - 22 City 28 - 30 highway.
Subarus run notoriously rich, even with the proECM it's still gona run rich, unless you can find the perfect fuel to air ratio your mileage isn't gonna get any better.

Plus the 91 octane is kind of wasted money in a N/A car, I actually get better mileage from 87 or 89.
Bry.
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Old 12-20-2002, 12:42 PM   #13
Keith99RS
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Default Winter Gas

I'm not sure about elsewhere, but in New England they change our gas for the winter months to an oxygenated (I think??) version and our mileage usually goes in the gutter until spring. Mine has dropped pretty significantly. I run 87 - 89 octane. This change is supposedly for the environment, but you burn more of it than normal, go figure.
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Old 12-21-2002, 01:00 AM   #14
Jademonkey
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IMHO, you don't need 91 unless you're getting pinging. Run 89 or 87; a few tanks of each octane, and see what gives you the best mileage.
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