school me on 85 octane

[Scott@Hightech]

So I am scratching my head here, wondering how my post is incorrect and wondering how I said the knock sensor DID NOT cause the ECU to change timing.

Scott, I like you and all that but please give me some hard data on your "emissions standards" quote from above and also the range of efficient adjustment of timing. R e t a r d i n g timing simply causes your vehicle to be less efficient, which will happen if you run 85 at lower altitude. The engine is having to make an adjustment that it would not have to make if you are running 87.

EDIT: Ahhh, I now see where my wording "Low end of the range is 87 Octane" can be misconstrued. Should not have worded it like that. How about "Low end of the range could be exceeded and degradation of performance is possible if the fuel is outside of manufacturer specifications" or some shit like that.

ANOTHER EDIT: Yep, "changes mixture" should not have been there either. I meant "changes timing." I need to get out of this conversation lol.

Not trying to beat a dead horse but, I dont understand your wording of "range" there isnt a + or - here. There is only the amount of knocking, the more the engine knocks the further the timing gets retarded. Lets say that your engine at 2500 rpm cruise is 15deg advanced. The engine starts pinging due to not enough "octane"(its burning out too fast). The knock sensor detects this and tells the computer. The computer then pulls some ignition timing. Lets say 1 degree. If its still too soon it will continue to ping. and the process repeats until is stops pinging. If it were bad enough to pull all the timing out of the computer you would have a lot of other issues, such as A/f ratio issues and engine power would be serverly reduced. You or the computer would notice those things before though.

As far as the emissions standards go. There is a TON of reading you can do on google about the lenghts manufactures go through to get vehicles to conform to current standards. Such as toyota and their 0w20 oil that is "required." there are so many factors that come into play that they have to define what to use so that results are repeatable. If this doesn't make sense PM me and we can discuss further.

 

[Scott@Hightech]

The lay person like me would've just figured it really makes absolutely no difference...kind of like running 87 and 89 at sea level.

This is probibly the most accurate statement, lol. You would probibly see a difference on a dyno, most most people would never notice.

However if you were to dyno your truck at sea level with 87 and again at 5000ft. you would see a HUGE difference. Much more power can be had with denser air(hence Forced induction)

 

[LandCruiser]

My front door is at 7200 feet, no matter what grade gas I run the 4Runner is on the wheezy side compared to at or below sea level.

Thanks for all the input about the gas, I don't want to damage the truck's engine and (as usual) I never got really clear answers from the dealer about 85 octane except that it is "trash gasoline."

If I stay up at nosebleed elevations, I don't know if 85 will really damage the engine--but will just feed it to the Land Cruiser and not the 4Runners, although my wife has been using it the two months she has been here without knowing any better.

 

[BeeRunner]

I made a mistake

So i've pretty much stayed on the west coast my entire life. Regular gas over here (california, oregon, washington) has always been 87 Octane. I recently traveled away from the west coast on a road trip and without realizing it at the time put regular (which in this state was 85 Octane) in my brand new 2017 4Runner. In one case I may have even put 83 but for the most part I used 85 octane for probably about 1,800 miles on this road trip. I remember a slight engine knocking one morning for a while but not being mechanically inclined I just said "meh, i'm at high altitude, maybe that's whats making it sound different". I made it back to Oregon okay but as soon as I hit the west coast I noticed I had a made a mistake in regards to gas used and I actually took the time to look up the suggested octane level in the manual and face palmed. Is there a way to tell whether i've done any damage to my engine? Hopefully someone more mechanically inclined than I can help me figure out if i've likely wrecked something or dramatically reduced the life of my engine.

 

[17KT4R]

Pre-detonation for an extended period of time at very high rpm will do wonders for your pistons, rings etc. It is highly unlikely these motors will be bothered by slight detonation during short periods which you describe.

I put 250 thousand kilometres on a 2000 Jeep TJ 4.0L inline 6, which required driver observance of throttle levels to avoid detonation for most of its life, or you could use any gas above 87 octane. That motor had perfectly even compression and plugs came out perfectly coloured every time, never burned oil etc. I know, completely different build than these 4.0's but the point is, occasional detonation is no big deal - you back off the throttle a bit which you probably did, not lay into further for the rest of the trip.

Do something nice for your truck now (run a few tanks of the highest octane you can find) and promise it to never do that again LoL :smash:

Just kidding - high octane won't do anything for it either. Next time you drive out that way - just throw a bottle of Octane Boost in with each fill up.