Welcome to the North American Subaru Impreza Owners Club Wednesday November 22, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Thread Tools Display Modes
Old 10-24-2000, 10:12 AM   #1
Jonathan Kent
Question changing octane and ECU reset

Hey folks. Can someone please clarify as to whether or not an ECU reset is necessary after changing gas octanes? I've always used 93 in my 99RS. However, this past weekend, I filled my empty tank with 87 for the first time. I didn't notice any changes (power, mileage, etc.)

So, to ECU, or not to ECU?


J. Kent
* Registered users of the site do not see these ads.
  Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 10-24-2000, 03:00 PM   #2
Scooby Newbie
Member#: 251
Join Date: Sep 1999
Location: Chicago, IL
1998 Impreza 2.5 RS


I'm not sure how long it takes the engine to notice the lower octane, but I've heard that it takes 3 tankfuls of a higher octane for the ECU to adjust.

I would only reset it when you go to a higher octane than 87. Why the change?

cakagan is offline   Reply With Quote
Old 10-24-2000, 03:47 PM   #3
Scooby Newbie
Member#: 2659
Join Date: Oct 2000
Location: Aberdeen, Scotland

The ECU should adjust to the lower octane quite quickly on a MY99, a reset should not be required.

The whole ECU reset is a subject of great debate here in the UK, but my simple understanding is that MY98 models or later should never need a reset, not sure about pre MY98 ones......hmmmmmmmm

sasim is offline   Reply With Quote
Old 10-24-2000, 04:10 PM   #4
Scooby Specialist
Member#: 1361
Join Date: Apr 2000
Chapter/Region: Tri-State
Location: Used to be Long Island/NYC...
1999 Legacy GT Ltd.
2006 Rav4 Sport Silvarrr


$$$ is why'd i'd change too...
silverSurfer is offline   Reply With Quote
Old 10-24-2000, 05:56 PM   #5
Scooby Newbie
Member#: 1322
Join Date: Apr 2000
Location: Silicon Valley
2000 2.5RS Sedan
72 Datsun 240Z


In case you don't already know....

You don't need high octane gas unless you are experiencing detonation. Just fill it up with the minimum octane required by the manufacturer and live happy. As you do mods to your car, upgrade to the next octane if you detect any knocking. Most mods outside of cams or forced induction will not require an increase in octane. To use the highest octane available just because that's what all the "sports cars" use is a waste of $$$ and gas mileage. You'll actually get better gas mileage with the least octane. Higher octane fuels are less prone to detonation because they are more difficult to burn. Being more difficult to burn means they burn slower and also are more difficult to ignite by your ignition system. So, unless your car was designed or has been modified in such a way to warrant the higher octane, stick with what works and enjoy the savings.

'00 Subaru 2.5RS Sedan
'00 VW Passat GLS 4Motion
'72 Datsun 240Z
Catfish is offline   Reply With Quote
Old 10-24-2000, 06:01 PM   #6
Scooby Guru
Member#: 114
Join Date: Jul 1999
Chapter/Region: MWSOC
Location: Wichita, KS and Whoring, OT
'03 Evo, Rice White
'01 Erion CBR 929


Flame speed is not related to octane.

You can trust me on that or you can read a very informative post here: http://www.i-club.com/ubb-files/Foru...ML/003898.html

In it you will also learn that engines can require considerably different octanes depending on wear, atmospheric and local conditions, and manufacturing tolerances. It is by no means unreasonable to think that some 2.5RS will require 91 octane or above to attain nominal performance, and others will require less than 87.

[This message has been edited by ColinL (edited October 24, 2000).]
ColinL is offline   Reply With Quote
Old 10-24-2000, 11:05 PM   #7
ImprezaRS dot com
over boosted again
Member#: 1458
Join Date: May 2000
Chapter/Region: RMIC
Location: Colorado Springs CO USA
2017 WRX Limited
2015 Forester XT, Tribeca



Don't you know that nobody ever reads that post? Except me...

ImprezaRS dot com is offline   Reply With Quote
Old 10-25-2000, 08:19 AM   #8
Liquid Calm
Scooby Newbie
Member#: 2744
Join Date: Oct 2000
Chapter/Region: South East
Location: Orlando, Fl
2005 STi


WOW that was a long post.....but some stuff I did not know in there
Liquid Calm is offline   Reply With Quote
Old 10-25-2000, 11:12 AM   #9
Scooby Specialist
Member#: 102
Join Date: Jul 1999
Location: The meeting place

Bah that post is like Colin's Tne Commandments tablets.
Gambit is offline   Reply With Quote
Old 10-25-2000, 12:58 PM   #10
Scooby Specialist
Member#: 2399
Join Date: Sep 2000
Location: fremont, in the bay man
2001 Impreza RS

Thumbs up

That post was crazy long.
MY01 BRP Sedan
BongMan is offline   Reply With Quote
Old 10-25-2000, 10:09 PM   #11
Ken Levin
Scooby Specialist
Member#: 1416
Join Date: May 2000
Chapter/Region: BAIC
Location: SF Bay Area
2/01 WRX SportWagon
Aspen White


I get improved mpg with 92 octane vs. 87 or 89 with my EJ22. Enough to make the added $ worth it.
Ken Levin is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
p0031 and misfires after a brand new front o2 sensor and ecu reset 1gcrazy Newbies & FAQs 25 09-26-2008 01:17 PM
GanzFlow aftermath and ECU reset question heatseeka Normally Aspirated Powertrain 16 06-19-2001 03:21 PM
Intercoolers and ECU Resets Kevin Thomas Normally Aspirated Powertrain 2 03-09-2001 10:55 PM
AFC and ECU reset Spectre23 Normally Aspirated Powertrain 0 03-03-2001 11:06 AM
Went to 89 octane during ECU reset.. is it okay? Jason52 General Forum Archive 1 12-21-2000 02:08 PM

All times are GMT -4. The time now is 08:32 PM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.