KR is knock retard. The computer (PCM) retards the timing when either of the two knock sensors report back enough noise level. The noise is typically predetonation caused in a forced induction setup. Normally aspirated cars can also have KR from running low quality fuel. This is why in the owners manual of your 99 it tells you premium fuel only. Run 93 octane and you should be at 0 KR. Start modding the wrong ways and you will notice KR and a loss of power. Mod the right ways and power increases and makes you smile.

It stands for Knock Retard. "Knock" is when there'* too much heat in the intake charge, and "detonation" occurs in the cylinder. "Detonation" is when the air/fuel mixture in the chamber ignites before the piston is ready, and can cause damage to the piston, valves, etc.

"Retard" is what happens when the PCM detects knock through the knock sensors, and pulls your timing and spark to stop the detonation. Although the PCM is pulling your timing and stopping the detonation, damage can still occur if too much happens. 7* or more of knock retard can start to damage components if done too much.

That'* why we recommend opening up the intake, and going with a FWI (Fender Well Intake) so that the intake is constantly pulling in cool air. That will help with KR. Even then, in order to go much smaller than a 3.4" pulley, you'll need to start going with higher ratio rocker arms, headers for the exhaust and a high flow cat before going any smaller.

TWM....The PCM doesn't pull spark, only retards the timing to keep the charge from being compressed enough that predetonation occurs.

Any sustained KR can possibly cause engine damage, however if KR is detected the PCM will do what it has been programmed to do to keep it from happening. IF a knock sensor fails and does not pick up KR then you will most likely damage the engine.

I have not yet heard of a knock sensor ever failing, this does not mean that they can not fail.

Wow, ok. Thought it performed two functions rather than just one. The main thing I wanted to get across, though, is that the PCM only helps to save the engine, and failure is still possible if the KR persists.

Running a 3.2" pulley when you have KR with the 3.4", for instance, is not a good idea. Even continuing to run the engine hard with any KR with any size pulley is not a good idea.

Just remember one key point:

For KR to be registered by the PCM, knock must ALREADY have happened.