While we are on the subject, let'* mention False KR. The knock sensor is essentially a microphone that listens for detonation in the combustion chambers. Detonation or pre-ignition occurs mainly when the ignition timing is too far advanced for the octane rating of the fuel. Detonation is a light, sharp clattering sound, something like shaking a couple of nuts in a metal can. So, if the knock sensor "hears" something that sounds like detonation, it is reported to the computer as a knock count. Depending on how many knock counts are reported in a given time interval, the computer will retard the ignition timing until the knock count reaches an acceptable level. The reduction in timing (knock retard, KR) can be as much as 17-20 degrees. That feels about the same when you are trying to accelerate as hooking another Bonneville to the back of your car.
False KR is when a sound other than detonation, like a sticking hydraulic valve lifter or a worn piston pin, or a worn rocker arm (tick tick tick) is picked up by the knock sensor and reported to the computer. The computer retards the timing until it reaches its set point (something like the 17-20 degrees mentioned above) because the sound never goes away. The fix for false KR in our cars is to repair the mechanical problem so that the sound that is mistaken for detonation is eliminated. If you suspect that your computer (PCM) is retarding spark due to false KR, simply unplug the knock sensor(*) and see if the car runs better. With the sensors unplugged, the PCM will default to 10 degrees of KR. 10 degrees of KR will make your car run pretty slowly, but is noticeably better than 17-20 degrees.
I know all this stuff because I have a mechanical noise in my engine that caused the computer to pull the maximum KR it could. After replacing all my lifters and installing new rocker arm bolts and checking for everything else, I suppose that the little, light, tick tick tick in my abused old engine is probably a loose wrist pin. Now, a car can run with a ticking lifter or a worn wrist pin for a long, long time. But, if the noise causes 20 degrees of false KR, you won't want to drive it for long. I resolved the problem by disconnecting my knock sensors and wiring in a couple of resistors that provide the PCM with the same information it would receive if the knock sensors were hearing nothing. So, I no longer have the protection afforded by the knock sensors, but the false KR is gone. This is not something I would recommend others do, as detonation can cause serious engine damage. And with no knock sensors to minimize that damage, your engine could be destroyed.
When my tired old engine finally fails and/or when I find a good buy on a replacement, I will be interested to see what damage has occurred to my pistons as a result of my redneck fix.