What exactly does a knock sensor do? And why would you need to replace it?

 

its junk. thats all i know.

 

faq.. read it.. it's a quite amazing thread up there at the top.

 

couldn't find it in faq

 

A knock sensor detects when the combustion mixture in cylinder is igniting before the spark fires (begining at a place other then the spark plug electrode) This is called pre-ignition. The knock that you may or may not hear is the multiple combustion fronts colliding and causing various engine parts to resonate. This is bad for your engine and can destroy it very quickly (although I had an 81 Volvo that knocked badly from when i hit 200,000 miles until I sold it at 250,000 miles). By using higher octane gasoline, the knock can be eliminated since the higher octane reduces the tendency to ignite. Cars that use high compression ratios, such as your Maxima, use higher octane gas (91+) to keep knock from happening.

The knock sensor listens to the engine to detect knock as early as possible and change engine operating characteristics to try to eliminate it. It does this by retarding the ignition timing. I believe a Maxima has ignition set at up to 18 degrees before top dead center under acceleration and 0 degrees at cruising speed (low engine load). If you have a bad KS, the Maxima always sets the timing to zero degrees to minimize the chances of pre-ignition since it no longer has its ears to go by. The bad news is that engine performance is inhibited (loss of low end power) as a result.

If you are using 91+ octane gas, you should not experience knock. If you are driving around with a bad KS, you will loose performance, but the engine will be protected (you may experience a loss in mileage). If your ECU is throwing a KS code and you want to get back to maximum performance, change your knock sensor.

 

got it, thanx

 

3rd to last post in the faq.. the real friggin long one