how common is knock?

[Only4U]

i know that engines get knock in them from time to time, but how common is a small degree of knock for most engines? and is most knock audible or is a lot of time knock so quiet that we can't hear it. what causes it? also, what is the negative aspects of knock and besides higher octane, what can you do to fix knock?

[black98V6]

well first off knock is also known as detonation!.. maybe that will help to understand how bad it is.. basically the fuel/air is igniting too early and the explosion is happening before the piston reaches top dead center.. forcing it down when it is supposed to be up this can lead to ALL kinds of things..
knock can be caused by fuel that ignites too early and higher octane can help the problem but if you have a 3800 that has knock the problem is not your fuel.. going to a higher octane to eliminate knock is not a solution to a problem it's a bandaid fix.. if that much of a fix..

you can get knock from the motor running too hot and the heat causing the fuel mix to ignite before the spark goes off.. it can be caused by deposits in the compustion chamber that hold heat and act kinda like a glow plug in a diesel.. basically they hold heat from combustion and ignite the fuel before the spark plug can..

having too high of a compression ratio can cause knock.. this is usually when you run lower octane gas through a higher compression ratio engine.. (above 10 to 1)

usually you can hear knock if you know what you are listening for.. but it has become aparent to me.. and maybe to others here that our motors make a ticking sound.. be it injectors or whatever it is common..

also if you are getting knock you should notice some loss of power..

the computer has sensors to recognize the detonation and retards timing.. basically it makes the spark go off later in the compression cycle.. this can auctually make the full combustion happen after the piston has reached top dead center..

that's prettymuch most of what I know about it..

I really do believe that our knock sensors are somewhat too sensitive just from what I have read here but have NO evidence to back this up..

[ August 14, 2002: Message edited by: black98V6 ]</p>

[Only4U]

<blockquote>quote:</font><hr>I really do believe that our knock sensors are somewhat too sensitive
<hr></blockquote>

meaning what?

oh ya, and how common is knock among our engines? does it fix itself eventually, or no?

[ August 14, 2002: Message edited by: Only4U ]</p>

[black98V6]

dunno about the commality of knock.. but it seems that some people seem to have knock retart alot but shouldn't be getting a knock condition.. like I said though just based on general observations here.. and the way MY car runs better some days than others.. don't have longs to back this up.. (but I soooo want a laptop and some logging software)

[Guardsman]

It's not uncommon for the engine to start getting detonation under heavy load at high rpm - with the later LT1s and LS1, they were designed knowing that they would get detonation at the high end (the higher compression allows more power to be made across the rpm range) and the knock sensors and the PCM knock retard counter it. Our engines, although lower compression, will still get it if you lean out the mixture enough (more air in, hotter spark), even the 3.4s can get it at the top end.
However, you shouldn't get any detonation at the low and mid rpm range, if you are, then you may be using bad gas, or there may be a timing problem. If you get enough detonation at the top end that you can actually hear it knocking, there is something seriously wrong. As black98 said, the knock sensors should pick up the detonation long before you can here it, and the PCM should retard the timing.
The negative aspect of knock is that it can literally beat your pistons apart and/or burn a hole in them if it's severe enough and/or happens enough. That usually results in your engine deciding that it wants to become a grenade one day when you're on it hard.
The way that you counter knock is by either cooling the combustion event, or delaying the timing (which cools the combustion event). If there are deposits in the engine that are causing the detonation, then higher octane gas, and/or cleaning out the deposits is the only way to stop it.

[Only4U]

well my dad has a tercel and it has a knock problem and the sound is like a ringing noise on the higher speeds. i noticed a similar ringing noise, only much quieter on my car when i'd hit between 2k and 3k rpms. well, i've also figured out that it is only coming from the driver's side of the hood lol. SO i'm pretty positive it isn't knock, but my air intake. i forget how loud the freaking thing is when my music is on. of course, when the music is on i can't hear it at all and when the music isn't on, i can hear it steadily increase and then when i get past 3k rpms, the exhaust is so loud i can't hear anything.

that is why i was asking though, cause i was wondering what the noise was. but i'm almost positive it's the air intake. thx guys.

[ August 16, 2002: Message edited by: Only4U ]</p>

[kaygee08]

You may be hearing your valvetrain, I hear this also from time to time.

[vtv6firebird]

Well for 3 years I have had to use 93 octane because of knock. No one, dealers included know why. It only happens at RPM's in the 2000-3000 range. Usually on the bottom end and dies out around 3000 RPMs. It sounds horrible. Have tried every trick in the book but it seems I have to keep throwing my money into 93 octane.

[Only4U]

heh, that's crappy. mine is so quiet i really couldn't hear it until i was listening for it. i don't what yours sounds like, but mine is like a whistle type noise...like what the intake sounds like at low throttle, only higher pitched. and the fact the it comes from the drivers side of the car makes me think that it's the intake.