Profile Correction

Profile correction software is used to learn and correct for mechanical inaccuracies in the crankshaft position wheel tooth spacing. Since the sum of all the angles between the crankshaft teeth must equal 360 degrees, a correction factor can be calculated for each misfire sample interval that makes all the angles between individual teeth equal. The LDR system learns one profile correction factor per cylinder (that is, 3 correction factors for a 3 cylinder engine or 4 correction factors for a 4 cylinder engine), while the HDR system learns 36, 40 or 60 correction factors depending on the number of crankshaft wheel teeth (that is, 35 for some V6 and V8 engines, 39 for V10 engines and 58 for some I4 and V6 engines). On some vehicles, the profile correction for both LDR and HDR systems will be common and will learn a separate profile correction factor for each individual tooth on the crankshaft position wheel.

The corrections are calculated from several engine cycles of misfire sample interval data. The correction factors are the average of a selected number of samples. In order to assure the accuracy of these corrections, a tolerance is placed on the incoming values such that an individual correction factor must be repeatable within the tolerance during learning. This is to reduce the possibility of learning incorrect corrections due to crankshaft velocity disturbances.

Since inaccuracies in the wheel tooth spacing can produce a false indication of misfire, the misfire monitor is not active until the corrections are learned.

Two methods of learning profile correction are used. The first is neutral profile correction and non volatile memory and the second is customer drive cycle for profile correction 97 to 64 km/h (60 to 40 MPH deceleration).