Thorby

I am too cheap to use the more expensive petroleum based fluid my car needs (I really don't want this thread to be popooed by saing the g** word). What I do when the engine starts to knock is to ease my foot a little off the accelerator so that it doesnt make such an awful sound.

The question, though: What exactly does the knocking do to my engine as far as damage?

86maxima96

iTrader: (10)

you actually hear knocking? your KS must be way gone. isn't that suppossed to keep the engine from knocking almost instantly? doesn't a sensor evaluate the fuel and then report to the EDU to 'slow down' or do what it does to keep knocking from occuring in the first place?

killerVQ30DE

For the $3-5 you save, you'll pay it back 10fold with a replacement engine and labour to put it in you'll come back crying soon saying your engine is fried

Thorby

My ECU is not reporting any problems with the knock sensor...

I dunno, also maybe its because of the hot dry environment of my city that the knocking gets nasty (not to mention the crappy gasoline we get in Mexico). Most of you guys who use the wrong octane DONT hear knocking?

86maxima96

iTrader: (10)

honestly, I didn't even think that there really was a 'knocking'! I just thought that it was a term giving to the activity of the engine at a certain time. perhaps it pings, once or twice, but then the ECU should find the correct timing or whatever it adjusts (wow, I should learn more) and the pinging is gone. hmmm.

zander

iTrader: (2)

Hmm... Do you change your oil regularly?

Thorby

Yes, I do. I add a bunch of Cisco right throgh the cap on the radiator.

Just kidding.

But I do every like 3 months.

THEJEFFERATOR

possable premature wear to plugs, pistons, cylinder walls, heads etc. runs hotter, burns up oil faster, bad gas mileage....

MDeezy

iTrader: (27)

its harmful enough to bring the thought of an engine swap much more a reality.

Use the money your "saving" on gas and change your KS

f550maranello2

iTrader: (2)

dude if you can actually hear the "knocking" which acutally sounds more like pining, then you need to do someting about it right now.. or just wait till the rings fry...

sonicrunch

do you like this?
This photo of a badly damaged piston indicates the effects of long-term engine knock.

sonicrunch

filter27e

What a confusing little diagram. It contradicts what I recognize as detonation, and since I learned it from a somewhat more technical and better explained source I'm going to stick with it (and I don't remember where so don't ask). Fuel prematurely ignited by a hot deposit and "flame fronts collide" is a kinda screwy theory.

Here's how it goes, basically and somewhat abridged:

Octane rating = % of fuel that is octane, rest is less expensive heptane OR rating = fuel with additives and similar compression characteristics. Of course you can't have something that is made out of 110% Octane (racing gas) so they add lead because lead SERIOUSLY increases a fuels ability to withstand compression but destroys the environment.

Higher octane burns SLOWER, but is more resillient to compression. More compression = more powerful stroke. If the fuel mixture reaches a compression point too high then it will ignite before the sparkplug fires.

Ideally, you want to BEGIN igniting the fuel just before it reaches TDC (top dead center). Full combustion should occur while the piston has begun to travel back down so the combustion carries it with more momentum.

Your car naturally can't change it's compression automatically, so cars that can run on 87 gas with adjusted timing have safe compression levels so the fuel doesn't ignite from compression, but the computer adjusts timing so the spark occurs later on lower octane fuels which burn quicker, and earlier for higher octane fuels which burn slower.

Detonation can either occur from using fuel that is too low of an octane rating to deal with the engines compression ratio so it combusts before the spark plug fires, or from bad spark timing that ignites allowing full combustion prematurely. Full combustion while the engine is on the upstroke is like hitting it with a hammer while it's being pushed up.

When your knock sensor is bad it should default to a safe timing level (gf's car has needed a knock sensor for 3 years before she met me) and assuming no other extreme environmental circumstances that could cause detonation, your engine should run fine just a bit underpowered. If the bolt on top of the knock sensor isn't tightened down enough, it's possible it could not be getting good readings but the ECU would still detect a "good" knock sensor and advance timing until it hears knocking. If you're running lower than 87 octane gas then that's a different story (compression detonation).

So what octane gas do you have in mexico?

Shift_my vq

I have a jim wolf ecu at high elevation and only 91 octane. And i hear and audible knock on a daily basses. Pretty much anytime it's hot outside or I go heavy partial throttle. Knock sensor takes longer than you would think to correct it but it's not very long. Maybe a full second or so. Not the instant you would hope. I hate it so much I usualy run 3 gallons of 110 unleaded and and 5 to 6 of 91 octane. After that knock is complety gone. At the track I have even used 130 leaded fuel. Not recomended but not really as bad as people say. I thought it was awesome. I have a buddy with and srt4 with no cats and tricked 02 censores that' used leaded gas for over 30 k miles. Still not recomended though. But I would say don't skimp. I hate buying race gas but I do it. Oh and by the way my max runs increcible on leaded gas. Kinda wish it was safe to use.

RockfordMax

iTrader: (2)

lol just keep the exhaust away from teh little kiddies

MaximaSE96

iTrader: (8)

ok to get rid of the myths.....u can use 87 coctane.....ur ECU will automatically retard timing so it doesnt knock......unless ur knock sensor is bad but then u would have retarded timing anyway.......basically by using 87 ur gonna lose a few degrees of timing and will sacrafice a little power......and it wont hurt ur knock sensor....because ur knock sensor works the same no matter what coctane u are using it just tells the ECU how to accordingly adjust timing.......

SkinnyMax

iTrader: (1)

The only time the knock sensor will tell the ECU to retard the timing is after it detects knocking, therefore everytime your timing it retarded you have already had knocking occur which like was said earlier can be horrible for the life of the engine. The worry is not "wearing out" the knock sensor the worry is ruining the engine.

MaximaSE96

iTrader: (8)

yes but even with 93 it still advances timing until it detects knock...so even there ut gonna get a hint of knock before it retards timing back to a safe setting

sonicrunch

It does not advance the timing until it detects knock. It simply runs the more aggresive timing map.

When it detects knock it reverts to the weaker map.

Northern Maxima

Man, you gotta start using at least 91 octane! It really doesn't cost a whole lot more than regular and most people get better gas mileage on it anyway. I bought my car knowing that I would have to pay a little bit more for premium and it definitely was something I wasn't too happy about doing but now I'm used to it and my Maxima runs way better than my old one did on 87.