I have a '99 2.5 RS... If i ran 91 octane, do i need to reset the ECU?

and how would i do that if i wanted to?



-Gagan

i don't see why you need to reset the ECU if you were gonna switch to 91 octane. i go from 89, to 91 sometimes and back to 89, depending on how much money i have.

as for resetting the ECU, you gotta disconnect the battery. then get in your car and step on the brakes a couple time (to drain out any power still left in the car). just leave your car like that for an hour or so. then plug battery back in. turn ign to the ON position (2nd click, where car isn't start but windows roll up), and leave it there for about 30 sec. then start the car, and let it idle for about 15 minutes. then shut car off. turn car on, and drive easy for the first day, and drive however you drive the next few.

jansen

u cant clear the idle learning even u disconnect the battery for an year, u must use SUBARU SELECT MONITOR to clear the momery , this is the only way to re-set the idle learining for OBD2 subaru

Why would you want to run 91 octane? Are you pinging?

Joe: No... I was just wondering... Of course, i'd get more performance out of the car if i went 91... I'm also going camping this weekend and theres a total of 4 guys, fully grown guys... that's weight... plus gear and all... i know how sluggish the car is when i got my brother and his friends in it when i pick them up from school (which always turns heads...). So i though, well, i put in 91 so that i get more power and response whikle drivign with the new load of people and gear.

Or, is there not a difference at all and i would just be wasting my $?

-Gagan

Sorry for the spelling of Octane...
Octance, what was i thinking?!?

-Gagan

I wouldn't waste my time...I thought about that before I went camping, and YES, with a car full of beefy guys (I'm not very small myself either), but if you did get any power gains, they'd be very minimal, not worth the time.

Just my 2 cents.
Greg

Higher Octane has been discussed a gazillion times on this website. If you do a search, you'll find a ton of info.

Basically, running higher octane WILL NOT increase the performance of your car or ANY car NOT DESIGNED to use it. Octane is just a rating system to indicate the fuels tendency to burn. HIGHER octane BURNS SLOWER than LOWER octane. The reason for high octane is to resist pre-ignition, which is when the air/fuel mixture is ignited by something other than the spark. When you compress a gas, it heats up and the more you compress it, the more it heats up. So, in a high performance car with very high compression ratio, the air/fuel ratio can be heated to a point at which the mixture will ignite on it's own due to the compression. Hence the reason for using a high octane gas, to resist this pre-ignition. Since all high performance cars use high octane for the reason listed above, uninformed people assume that high octane = more power. As you can see, that's hardly the case.

The basic rule of thumb regarding octane is only put it what you need. If your car runs fine on 87 with no pre-ignition, then that's what you should use. If you have some slight pinging, run 89 and see if it goes away. If you use a higher octane than is required/recommended, you won't do any harm, but you may actually LOSE performance due to the fuels slower burn rate.

What Catfish said is 100% on the mark. :) Mind if I steal it for inclusion in a FAQ?

:eek:

Woah.....

I've been enlightened (No offense to any Buddists!)

Dude, i didn't know that.... well then, my questions been answered.

so, i may be coming up to BC in december to see family in Surry... Any sugestions Joe?

-Gagan

Yes Catfish is 100% on the mark. On that note, if any of you turbo guys are looking for racing fuel, they are available at any Redwood Oil station if you are lucky to have one in your area. Luckily they are based up here! :p

joltdude, drop me a line when you make your plans, we can meet up. I might be driving to Thunderhill around Dec. 3 :)