High Data Rate System (HDR)

The HDR misfire monitor uses a high data rate crankshaft position signal, 18 position references per crankshaft revolution. This high resolution signal is processed using 2 different algorithms. The first algorithm is optimized to detect hard misfires on one or more continuously misfiring cylinders. The low pass filter filters the high-resolution crankshaft velocity signal to remove some of the crankshaft torsional vibrations that degrade signal to noise. Two low pass filters are used to enhance detection capability - a base filter and a more aggressive filter to enhance single-cylinder capability at higher RPM. This significantly improves detection capability for continuous misfires on single cylinders at redline. The second algorithm, called pattern cancellation, is optimized to detect low rates of misfire. The algorithm learns the normal pattern of cylinder accelerations from the mostly good firing events and is then able to accurately detect deviations from that pattern. Both the hard misfire algorithm and the pattern cancellation algorithm produce a deviant cylinder acceleration value, which is used in evaluating misfire in the General Misfire Algorithm Processing section below. Due to the high data processing requirements, the HDR algorithms could not be implemented in the PCM microprocessor. They are implemented in a separate chip in the PCM called an AICE chip. The PCM microprocessor communicates with the AICE chip using a dedicated serial communication link. The AICE chip sends the cylinder acceleration values back to the PCM microprocessor for additional processing as described below. Lack of serial communication between the AICE chip and the PCM microprocessor, or an inability to synchronize the crankshaft or camshaft sensors inputs sets a DTC. DTC P0606 is set if there is a lack of serial communication between the AICE chip and the PCM microprocessor. DTC P1336 is set if there is an inability to synchronize the crank or camshaft sensor inputs. This change was made to improve diagnosis. DTC P0606 generally results in PCM replacement while DTC P1336 points to a camshaft sensor that is out of synchronization with the crank. Profile correction software is used to learn and correct for mechanical inaccuracies in crankshaft tooth spacing under de-fueled engine conditions (requires 3 decelerations from 97 to 64 km/h (60 to 40 mph) with no-braking after the keep alive memory (KAM) has been reset). If the KAM has been reset, the PCM microprocessor initiates a special routine which computes correction factors for each of the 18 (or 20) position references and sends these correction factors back to the AICE chip to be used for subsequent misfire signal processing. These learned corrections improve the high RPM capability of the monitor. The misfire monitor is not active until a profile has been learned.