[mwebb]

this shows knock retard per cylinder in a VW Passat
Knock retard is the correction in ignition timing to prevent spark knock .
this system has so much ping that there is around 60kw of knock retard at 40% of calculated load
which on this system will peak around 95% - here it is much less

consider that the 4 cylinder vw engine in the jetta from that year has only 85kw maximum power output

why ?
customer is using poor quality 87 octane in an engine designed for 93octane and has been for some time , heavy carbon deposits from partial misfires have increased compression ratio in all cylinders
the car can not get out of it's own way ....

there are no DTCs and the "check money" light is off .

this is what a system that has knock correction will do if you advance base ignition timing beyond specification.
on a system without knock correction , results can be much worse

fix ?
solvents injected to clean carbon from combustion chambers and a tank of the correct top tier premium shell gas -
customer did not believe the difference this would cause ... until he felt it .