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Gas mileage improvement with K&N air filter?


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14 replies to this topic

#1 go_mo_bryth

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Posted 26 October 2005 - 08:26 PM

Hey all,

Back again with more questions. Last week, we installed a new K&N air filter in our 95 Legacy LS and had hoped for more mpg. We DID get the horsepower boost but seems we are going through gas faster than we did with paper filter. Is this possible? I'm still driving it the same way. Used to get about 300 km out of a tank of gas, got about 200 last tank. Thanks to all who might/will answer. Gord

#2 rcoaster

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Posted 26 October 2005 - 08:55 PM

Hey all,

Back again with more questions. Last week, we installed a new K&N air filter in our 95 Legacy LS and had hoped for more mpg. We DID get the horsepower boost but seems we are going through gas faster than we did with paper filter. Is this possible? I'm still driving it the same way. Used to get about 300 km out of a tank of gas, got about 200 last tank. Thanks to all who might/will answer. Gord



Give it time. I installed one in my 96 Outback and did get the power boost, and did get an slight improvement on MPG. You will need to let the ECU adjust to the new filter.

#3 sc850r

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Posted 26 October 2005 - 09:00 PM

Any idea how much MPG gain youi got?

#4 go_mo_bryth

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Posted 26 October 2005 - 09:09 PM

Any idea how much MPG gain youi got?


That's what I'm not sure of sc850r. It is looking like a DECREASE in mpg right now. :( and that is NOT what I am after.

#5 oregonloyale

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Posted 26 October 2005 - 09:26 PM

I would manually reset the ECU so it can remap itself.
Also when you add more air the ECU sees it as running lein and starts to dump more gas in thru the injectors in order to richen it up.

#6 go_mo_bryth

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Posted 26 October 2005 - 09:37 PM

I would manually reset the ECU so it can remap itself.
Also when you add more air the ECU sees it as running lein and starts to dump more gas in thru the injectors in order to richen it up.


Hmmmm..... so how do I reset the ECU? It sounds like a plug-intervention is coming.... unplug the brain from the body and then replug it again? Sounds easy but is it?

#7 oregonloyale

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Posted 26 October 2005 - 10:43 PM

or unplug fuse #14 for about 15-20 min then plug it back in start car but dont touch the gas for about 1 min.
i think thats the way it goes.
Hold on Ill find the write up.

#8 oregonloyale

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Posted 26 October 2005 - 10:44 PM

Got it .
Borrowed from another fellow subie lovers site. Legacy777
http://www.surrealmi...aru/engine.html

#9 go_mo_bryth

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Posted 26 October 2005 - 10:56 PM

Got it .
Borrowed from another fellow subie lovers site. Legacy777
http://www.surrealmi...aru/engine.html


I went to the site Oregon but he says that the fuse technique only works on the 90-94's. Ours is a OBD II. So does that mean we need to do the battery disconnect for 45 minutes method? I don't want to go to the garage to get the ECU reset as it costs $60 just to get it hooked up. I'm a cheap Scot and don't like to pay for anything I can fix m'self. hahaha

#10 Setright

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Posted 27 October 2005 - 03:37 AM

Or be patient, the ECU will learn in due course.

#11 go_mo_bryth

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Posted 27 October 2005 - 07:19 AM

Or be patient, the ECU will learn in due course.

In due course huh? I do hope this doesn't take long Setright. At $0.972 Cdn a litre, I hope it's not a lengthy process. Mind you I s'pose it is probably more per litre where you are! :( Thanks for the info and have a great day/night. Gord

#12 friendly_jacek

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Posted 27 October 2005 - 09:26 AM

Hey all,

Back again with more questions. Last week, we installed a new K&N air filter in our 95 Legacy LS and had hoped for more mpg. We DID get the horsepower boost but seems we are going through gas faster than we did with paper filter. Is this possible? I'm still driving it the same way. Used to get about 300 km out of a tank of gas, got about 200 last tank. Thanks to all who might/will answer. Gord


In some cases, K&N filters can foul up MAF sensors. Clean yours. There is no f***ing way ECU reset will help you if you have dirty MAF. Google for MAF cleaning, as it is easy to damage one.

#13 trxeslr66

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Posted 27 October 2005 - 09:38 AM

in a 99 Legacy 2.2 I was getting 18 or 19 city with paper a paper filter. Changed to Fram Air Hog, (Same concept as K&N) for $45 and it made a power differance AND mpg differance. When I drive it easy I get about 23-24 city. Highway gets into the 30's. I Never hit 30 with the paper filter.

If the filter is too saturated in the oil spray it could cause the reverse effect this filter is supposed to have.

Have you resolved this problem yet?

#14 oregonloyale

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Posted 27 October 2005 - 02:50 PM

I have cleaned many a MAF on VW, as they are my primary tuning vehicle.
Remove Maf from inttake.
DO NOT TOUCH THE INSIDE OF THE MAF!!!!!!!!!!
I cannot stress that enough , they are brittle and easliy snap.
Get a can of Non conductive electronics cleaner.
The kind that leaves "0" residue and start spraying.
You can spray everywhere , its "0" residue and will not hurt the electronics as this is what the cleaner is for.
Others say get some alcohol based cleaner, I forget exactly what but then put the cleaner in a bag w/the maf and shake.
That is a NO NO in my book as it falls back to the fragility of the MAF.
Legacy777 can attest to the fragility of a MAF .
He foound out when he did the open filter element and didnt bracket it well enough and all the jarring around screwed up the MAF.
So anywyas back to the cleaning.
Once you have totally spryaed thpiss out of it let it sit in a nice room temp area and go have a beer, lets say 30 min.
Then come back inspect for any residue, I doubt there will be , and bolt it back up.
I would reset the ECU before firing it back up with the cleaned MAF , but thats just me .
This way I would be starting from scratch, so to speak.

#15 Slegacy96

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Posted 27 October 2005 - 04:51 PM

in a 99 Legacy 2.2 I was getting 18 or 19 city with paper a paper filter. Changed to Fram Air Hog, (Same concept as K&N) for $45 and it made a power differance AND mpg differance. When I drive it easy I get about 23-24 city. Highway gets into the 30's. I Never hit 30 with the paper filter.

If the filter is too saturated in the oil spray it could cause the reverse effect this filter is supposed to have.

Have you resolved this problem yet?


What do you floor it everywhere? I get 22 mpg in my '99 2.5.




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