i have a newb question, what does the knock sensors actually do? i know they are located under the intake but what purpose do they serve,and how do you know when one is bad and needs to be replaced

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They detect detonation in the combustion chamber. Detonation is the pre-ignition of the air/fuel in the chamber BEFORE the spark plug fires. When this happens you get the flame front from the detonation hitting the flame front from the spark plug=very very bad. It can literally punch a hole in the piston. It makes an audible knock or ping, which the sensor detects, and if it detects "knock" it retards the timing BIGTIME which cools the cylinder (big power loss too) to prevent the knock from re-occuring. They usually don't go bad, BUT certain things can set them off, ie:false knock. Headers emit so much underhood noise that sometimes they trigger the sensor into thinking it's hearing detonation, thus killing the timing, also roller rockers have been known to do this. Most people who modify their cars to a large degree ie: cams, heads, etc, go into the computer and delete the knock sensors ability to alter timing, and ALWAYS run premium fuel.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

Nice awnser Joelster. Took teh words outta the good book of LS-X tuning.

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23:23] blkIROC355: sometimes when i pee i make that sound the light sabers make
[23:23] SpecialK LS1: lmao
[23:23] blkIROC355: and play with the stream
[23:23] SpecialK LS1: that's just wrong