Ignition Misfire Recognition

Ignition Misfire Recognition:

OPERATION:
When the air/fuel mixture fails to combust in the cylinder, it proceeds unburned into the exhaust system. The immediate effects are a loss of performance and higher emissions. Even more significant is the danger of damage to the catalytic converter as a result of overheating due to increased levels of catalytic combustion.
The misfire recognition function is based on the ability to trace uneven running to the cylinder at which the problem is originating.
Irregularities in the road surface could be falsely interpreted as misfire. To compensate, the engine-management system is equipped to activate the misfire recognition function when the vehicle is operated on rough surfaces.

OBD II CHECKS:
- The misfire rate, during testing initiated at fixed intervals of 1000 crankshaft revolutions. Increases in HC content by a factor of 1.5 corresponds to a miss rate of > 2%.
- The misfire rate relative to instantaneous operating conditions (rpm, load factor) at an interval of 200 crankshaft revolutions.




Procedure:
During misfiring, the crankshaft experiences additional fluctuations in its motion.




If misfiring occurs, the rotational speed of the crankshaft Position disc changes. It is recognized by the starter ring gear.




The disc is divided into sections (for instance, three 1200 segments for a 6-cylinder engine). Together with the camshaft Position sensor it furnishes the system with the data required for selective recognition and identification of the cylinder(s) which are failing to fire.
Systems employing the starter ring gear to detect ignition miss incorporates a sensor rotor adaptation function to compensate for error/tolerances in the ring gear.

Engine-Speed Sensor G28:

Electrical Circuit - Engine-Speed Sensor G28:

SYSTEM COMPONENTS:
Engine-Speed Sensor G28:
Located on starter ring and used to determine the engine rpm. The engine will not start or will shut down if the speed signal is lost.

Engine-Speed Sensor G28:

Electrical Circuit - Engine-Speed Sensor G28:

Sensor for Ignition Timing Point G4:
The G4 is an inductive sensor. It is required to recognize the ignition - TDC for the third cylinder. If the signal is lost, the engine will not start.

Camshaft Position Sensor G40:

Electrical Circuit - Camshaft Position Sensor G40:

Camshaft Position Sensor G4O:
For Audi the camshaft Position sensor is used together with the signal for ignition timing sensor G4, to recognize the ignition - TDC of the third cylinder. The engine will not start if signal is lost.