Trooper II L4-2254cc 2.3L SOHC (1985)
Engine Control Module: Description and Operation
The ECM generates an electrical signal to the carburetor duty solenoid to control the air/fuel mixture as necessary. This signal continuously cycles the
solenoid between on and off time as a function of the input voltages from the sensors. The ECM control signal is selected from one of the following
operational modes:
1.
Inhibit Mode. No signal.
2.
Enrichment Mode. A fixed pre-programmed duty cycle signal.
3.
Open Loop Mode. A fixed pre-programmed duty cycle signal.
4.
Closed Loop Mode. A calculated duty cycle is generated based on oxygen sensor and other sensor outputs.
During closed loop operation, the ECM monitors the voltage output of the oxygen sensor. When the exhaust is lean (low voltage), the ECM commands
the carburetor to richen the mixture. When the exhaust is rich (high voltage), the ECM commands a leaner mixture.
The ECM can also store in memory the current duty cycle being used for either idle or off idle conditions. When the vacuum switch signals the ECM that
a specific condition exists, the ECM steps to the duty cycle last recorded for optimum operation. The slow cut solenoid valve, located in the carburetor,
is controlled by electrical signals from the ECM. The ECM senses coasting conditions by means of signals from idle position switch and WOT switch for
Pickup and Trooper II or clutch pedal and transmission gear position switch for I-Mark, then opens circuit to mixture control solenoid whenever engine
speed is above a predetermined value. This causes fuel flow to carburetor to be discontinued. The circuit to the slow cut solenoid is opened only when
the following two conditions exist simultaneously:
1.
With carburetor throttle valve at idle position, vacuum signal to vacuum switches are below or above specified limit.
2.
Engine speed exceeds specified limit.
