can knock be prevented?

[ADrewzki]

There are many threads out there that discuss how to fix the issue of knock. My question would be is there a way to prevent knock altogether? I know you can get the 2g knock sensor to go off with lifter tick as well as the phantom knock issue with a 1g swap throwing misfire codes. If timing is dead on and fuel trims are all good, knock really shouldn't be an issue in my opinion. So what exactly causes it? Also, when an engine knocks, it should be audible, correct? If my timing is getting retarded while driving, it might be a case of phantom knock as opposed to real knock if I can't hear anything, right? Thanks for the help guys. -Drew

 

[kpt4321]

My question would be is there a way to prevent knock altogether?

Sure, eliminate the sources that can cause knock. Of course, there are about a hundred different sources, some more important than others. As such, you just have to do your best to minimize their effect.

If timing is dead on and fuel trims are all good, knock really shouldn't be an issue in my opinion.

How do you know if the timing is dead on? How do you know what timing is dead on? How do you know what AFR at different load points is dead on?

If you somehow knew exactly what the perfect timing and AFR were for each throttle point, the need for a knock sensor would be much less (you'd still want one for other things, in my opinion, but it would not be as much of a necessity). However, you don't know.

So what exactly causes it?

I'm working on a tech article to explain all of this, but I'm wicked busy lately (work, school, shootout, etc) so I have not had time to finish it. Sorry!

Knock is basically caused by SOMETHING which makes the fuel and air mixture burn in an undesirable nature. That could be too much timing advance, too lean an AFR, too rich an AFR, hot charge temps, hot cylinder temps, hot spots in the combustion chamber, too low fuel octane, too high cylinder pressure, bad fuel... and much much more.

Also, when an engine knocks, it should be audible, correct?

Sometimes yes, sometimes no. With a 4G63, you usually cannot hear it.

If my timing is getting retarded while driving, it might be a case of phantom knock as opposed to real knock if I can't hear anything, right?

It could be, but since you won't usually hear real knock either there's nothing yo can do about that.

 

[ADrewzki]

Sweet. Thanks for the info. I'd love to see the tech article once you've finished it.

 

[ahains]

To expand on what was said above - knock is explicitly caused by too much heat and pressure.

Octane is directly a measurement of how much heat & pressure some fuel can be under and still burn normally. Once you exceed that maximum heat & pressure for a given octane, you will most likely get an explosion (detonation/knock).

On any modern turbocharged car you should not hear knock, the ECU is tuned for what knock "looks like" for its engine (displacement, among other parameters). The ECU will see knock long before you can hear it with the naked ear, and pull timing to attempt to stop it.

However, if you amplify the signal that is coming from the knock sensor, you may very well be able to "hear" it before the ECU can see it. The ECU uses algorithms to detect what should be knock, but the combination of your ear and brain has some intrinsically complicated algorithms (God is a good programmer ) that can hear it quite easily.

Check out this site if you want to hear it yourself:
http://home.netcom.com/~bsundahl/knock/sound/KnockSounds.htm#Knock

I just ordered a datalogging cable and am looking forward to comparing when the ecu begins to hear knock and when I begin to hear it

HTH,
Adrian

 

[ADrewzki]

Crazy. I'd like to know what gears you have knock in. I have a 6 bolt in mine and I'm hoping that it's just the stupid misfire code getting thrown causing my timing to retard. Thanks for the info.