Method for detecting malfunctioning turbo-diesel cylinders

A diagnostic method for diagnosing a misfire condition of individual engine cylinders in a turbocharged diesel engine having at least a first and a second cylinder, further comprising:

• one or more pressure sensors for measuring a pressure value in an exhaust path of the at least first and second cylinder;
• a crankshaft position sensor, for detecting a rotational crankshaft position;
• and
• a processor unit for reading the pressure sensor and the crankshaft position sensor;
• wherein the processor unit is arranged for performing acts of:
• obtaining a number of subsequent sampling pressure values (p1 . . . pm) of the pressure sensor as a function of crankshaft angle position;
• selecting a diagnosing test for diagnosing a misfire condition based on the obtained sampling pressure values;
• wherein selecting the diagnosing test is characterized by
• defining a group of diagnosing functions (f1 . . . fn), each having as inputs a selected number (Pα, Pβ) of subsequent sampling pressure values of a tuple P (p1 . . . pm) and having an output diagnosing a misfire condition when the diagnosing function (f1 . . . fn) is outside a threshold (t1 . . . tn);
• determining an error function (e1 . . . en), which is a function of measured false fails and false passes for said diagnosed misfire condition by said diagnosing function (f1 . . . fn), in each of an engine speed region, ranging from a lowest engine speed (rlow) to a highest engine speed (rhigh), for selected engine speed range intervals (s1 . . . sl), and
• selecting a diagnosing function fi from the group of diagnosing functions (f1 . . . fn), wherein fi having an error function ei that is lowest over the entire speed range ([rlow-rhigh]).