I have found that the Motronic 2.10.4 maybe too smart. I am using an interceptor to lean the AF mixture.
I have tried to lean the mixture at 3500 rpm for crusing with 50% load on a dyno. According the combustion in the Otto cycle, in a lean burn, detonation will happen at some point of time. Detonation on an engine can be heard like "clashing marbles".
But nothing on the Motronic. I have leaned it to a point that it was about to stall but no detonation occurs. Kudos for such a foolproof ECU. Bad news for me who want to tune a better car.
I have drawn 2 conclusions.
1. The knock sensor is too sensitive. So when it hears the slightest of pings or detonation, it retards ignition timing.
2. Ignition advance on the Motronic 2.10.4 is too mild to even cause detonation.
My bet will be on (1). My next experiment is to cut the knock sensor wire to the ECU.