Usage:
System Operation
The primary function of the ECM system is to electronically govern the engine. The ECM governor senses engine speed (using the engine speed sensor on the flywheel ring gear), then controls the fuel rack to achieve a desired engine speed. This test is used to determine if the ECM governor is properly controlling the fuel rack.
The variables displayed on the ECAP "Status Display" which are used in this test are:
Desired Engine Speed ("Des Engine RPM" on ECAP)
An input to the electronic governor within the ECM. The electronic governor uses inputs from the Throttle Position Sensor, Engine Speed Sensor and Customer Parameters to determine "Des Engine RPM".
Desired Rack Position ("Des Rack Pos" on ECAP)
The rack position where the ECM wants to move the rack, based on the ECM governor trying to maintain "Des Engine RPM". "Des Rack" will not go farther than the "FRC Rack" or "Rated Rack".
Actual Rack ("Rack Pos" on ECAP)
The ECM's interpretation of the signal from the Rack Position Sensor which represents actual position of the rack, assuming the sensor signal is valid. If the rack controls are working properly, "Actual Rack" should follow "Desired Rack".
Fuel Ratio Control (FRC) Rack ("FRC Rack" on ECAP)
FRC Rack Pos. - is a limit based on control of the fuel-air ratio and is used for emission control purposes. When the ECM senses a higher inlet manifold (boost) pressure (more air into the cylinders), it increases the "FRC Rack Pos" limit (allowing more fuel into the cylinders).
Rated Rack Position ("Rated Rack" on ECAP)
A limit on rack position which provides the specified power and torque curves. This value comes from maps programmed into the personality module at the factory.
For a better understanding of ECM governing refer to Section 1: System Operation page 6. A brief description of each variable can be found in Section 6: Glossary of ECM Terms.
Schematic
Functional Test
