I'm not sure if the ecu adjusts the mix from the input it gets from the knock sensor. It will definately retard the timing though. With a knock sensor, the engine can tune itself to the point where the engine is almost to knock. So you get better performance.
Detonation, knock, ping is an explosion ahead of the flame front. Bad for the engine.
Heres my two bits, start with distributor timing. The base timing is set by you, the mechanic. When the engine runs, the ECU adjusts the ignition timing for two reasons. First: to optimize operation conditions. Ie: acceleration, decel, pulling a load. Second, the ECU adjusts timing to regulate the idle - you can see this by hooking up a timing light and cold starting your truck. You'll notice the timing is advanced, then gradually creeps back. Another piece of info, your engine runs optimally when timing is advanced to the threshold of pinging. Of course, you don't really need your engine to run at its peak all the time (ie: idle, cruse, and decel), you'll only need this on wide open throttle situations. This is where the knock sensor comes in.
A knock sensor is a peizoelectric device that is tuned to "listen" for certain engine noises (knocks and pings) that occurs when the timing is too far advanced. If you open your throttle 100%, that means you need your engine to run at its peak, maybe to pass a car on the freeway or something. You usually don't operate at WOT for an extended period of time. So, the TPS tells the ECU that you want WOT, and the ECU dumps more fuel (increases pulse width) and advanced the timing. Your engine starts to knock and ping, the knock sensor (which works just like a microphone tuned to a specific frequency) "hears" the pinging, sends an electrical signal to the ECU to back off the timing. The ECU backs off the timing, the knock and ping goes away. The knock sensor stops sending a signal because it can't "hear" the knock and ping. The ECU advances the timing. The engine starts to ping. The knock sensor sends an electrical signal to the ECU and the whole cycle repeats itself continuisly. This is called "closed loop operation." BTW, usually, this happens so fast you won't be able to hear the ping. If you can hear a ping, that means either you've set your base timing too far advanced and the ECU is not able to electronically pull the timing far enough back to get rid of the ping, or there is a problem with your knock sensor circuit.
Although I'm not certain this applies for Toyotas (although I am quite sure its the same), but the closed loop operation between the knock sensor and ECU only involved timing adjustments, not fuel adjustments. In other words, the closed loop operation between a knock sensor and ECU is independent from the closed loop operation between the O2 sensor and ECU.
Ha I just got mine from the dealer 205.00 with tax. Guess what I still have a damm knock sensor code !!!!! But that is ok when the chevy v8 goes in the only electronics on the engine will be the dizzy.
PS anybody want to buy a knock sensor?
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