Vehicle applicability: This diagnostic supplement covers multiple Ford vehicles and engines. Follow the application named in the source below. Some references apply to vehicles other than Mustang.
Description and Operation 1-123
Misfire Detection Monitor
Misfire Detection Monitor
The misfire detection monitor is an on board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The misfire detection monitor is enabled only when certain base engine conditions are first satisfied. Input from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), and mass airflow (MAF) sensors is required to enable the monitor. The misfire detection monitor is also carried out during an on-demand self-test.
1. The PCM synchronized ignition spark is based on information received from the crankshaft position (CKP) sensor. The CKP sensor signal generated is also the main input used in determining cylinder misfire.
2. The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel mounted on the end of the crankshaft.
3. The input signal to the PCM is then used to calculate the time between CKP sensor signal edges and the crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria are met, then the suspect cylinder is determined to have misfired.
4. The malfunction indicator lamp (MIL) is activated after one of the above tests fail on 2 consecutive drive cycles.
Misfire Detection Monitor
Misfire Monitor Operation
The signal from the crankshaft position sensor and timing wheel is processed by the PCM into individual tooth period measurements and provided to the misfire monitor. The misfire monitor uses the tooth period measurements to calculate crankshaft acceleration signals for misfire detection.
A low data rate (LDR) and high data rate (HDR) are the 2 different types of misfire monitoring systems used. The LDR system is capable of meeting the federal test procedure monitoring requirements on most engines and is capable of meeting the full range of misfire monitoring requirements on 3 and 4 cylinder engines. It is also used on 6 cylinder engines with rear mounted crank sensors. The HDR system is capable of meeting the full range of misfire monitoring requirements on 8 cylinder and 10 cylinder engines. The HDR system on these engines meets the full range of misfire phase-in requirements specified in the on board diagnostic (OBD) regulations. The PCM software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the OBD requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle RPM.
The monitor includes a diagnostic check on the crank sensor input that checks the number of tooth period measurements received on each cylinder event. If the monitor receives an invalid number of tooth period measurements, DTC P1336 will set. This DTC indicates that noise is present on the crank sensor input or there is a lack of synchronization between the camshaft and crankshaft sensors.
Low Data Rate (LDR) System
2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015
2016 Mustang workshop publication supplied to Mustang Atlas. Original technical text and illustrations; HTML formatting by Mustang Atlas. Source page numbering is retained for traceability. Follow the configuration, revision, warnings, and cross-references in the material. About this edition.