There hasn't been an engine yet that I know of that has been released that used closed loop knock detection on whilst on "load".
That's because knock sensors are merely ultrasonic piezo shock sensors on the block. They pick up noises accross a certain bandwidth and the ECU then retards the timing the preset amount but only in "cruise" conditions.
This is perfect for the manufacturers. Eg you are cruising aloung the freeway at 110km/h, light throttle. The ECU goes into cruise mode, lean's off the fuel by monitoring the O2 sensor and simultaneously advances the timing to the point of detonation and then retards it by a few degrees. It then does this over 50 times a second. More timing = more power as you know so effectively you'll get the most power possible from a comparatively small amount of fuel.
This can't be done on "load" or above a certain RPM as the engine makes too much mechanical noise from things like the valves, pistons etc that is within the sensors bandwidth.
That's why the ignition maps are there, otherwise it would never need them. You could simply let the closed loop go on the knock sensors and it would always run to the most advance you could have with that fuel, that intake air, etc.
The ignition and fuel lookup tables are their cause they are safe and tested values programmed by the engineers at the factory. They are also conservative, which is where many of us can tinker and get some decent gains
Holden Commodores disregard knock sensor input above 3500rpm because there is too much mechanical noise.
Tue, 27 May 2003 09:53
