Ok, this is a noobish question....what exactly is engine knock(I know that it has something to do with timing-the computer retards timing when knock is detected), and are there any advantages to disabling the knock sensor(on any vehicle)? :cheers:

 

Knock sensor is supposed to be an indicator of detonation within the cylinders. I just bought but haven’t installed one from MSD. The unit has a light bar and audible alarm (adjustable) for engine knock/detonation. The idea is to detect detonation before it destroys the pistons and adjust ignition timing to prevent it. MSD also sells an adjustable advance control but I don’t plan to use it. You could go to the MSD website for a better explanation.
I can’t see any advantage to disable the knock sensor, as its function is to save the engine.
Okay a knock is usually caused by detonation when the fuel burns way to fast and cylinder pressures peak high enough to break things (pistons). Too high compression would do this.
Pre-ignition will cause knock also and is caused by some little hot spot/sharp edge in combustion chamber and the fuel burns prematurely. I guess too much timing advance is guilty of this.
Some people have posted that there’s very little difference between them but they usually have separate descriptions and you can decide for your self next time you have knocks in yours. :jester

 

Thanks! Just what I needed to know. :cheers:

 

The knock sensor itself is just a sort of microphone that screws into the block. The knock sensor is connected to a control box (ESC = electronic spark control - in GM FI) and this box gives the interpreted signal to the ECM which in turn instructs the EST to retard timing untill the knock is gone, then advancing begins again.

There are several versions of knock sensors and ESC boxes, the later (87+) models have an ignore circuit so they won't retard because of the noise of the roller cam setup. These will also work with a gear drive (not the very noisy types though).

It's VERY unwise to disconnect the knock sensor to get some more advance. When there's no knock the sensor won't pick anything up and there will be no retard as if it wasn't there. When there is knock you REALLY want that thing to work, it can save your engine. It's very desireable to run one with a FI setup. FI works by always leaning out the mixture, then enrichening when the O2 sensor detects a lean condition. This is done because the O2 sensor only can detect lean, if it's stoichiometric or rich, it'll look the same to the O2 sensor since all the fuel is burned (not counting severely richt to the point it won't ignite because then the engine won't run properly or at all)

So, this means the FI system will always run on borderline lean. This is why you have the knock sensor. Some old systems like the Bosh Jetronics *(some) and the Motronics don't have a knock sensor (and they have some other weird stuff on them, for instance weird idle controls) and those FI systems are just plain crap.