Engine Control Module: Description and Operation

CIS-E System:

The CIS-E control unit, which is located in the cowl at the left rear of the engine compartment, receives and evaluates information provided by various sensors concerning engine operating conditions. From the information received, the control unit calculates the appropriate output values for the differential pressure regulator, and the idle stabilizer valve which are needed to maintain optimum engine performance and emission characteristics. Input signals include:

^ Air flow sensor plate potentiometer
^ Coolant temperature sensor
^ Knock control unit
^ Oxygen sensor
^ Throttle valve switches

Differential Pressure Regulator:

The differential pressure regulator controls pressure in the lower chambers of the CIS-E fuel distributor, therefore, regulating the pressure differential across the metering valves and the volume of fuel that is delivered to the fuel injectors. It is controlled by a variable current output from the CIS-E control unit in response to different engine conditions.

After-Start And Warm-Up Enrichment Graph:

AFTER-START AND WARM-UP ENRICHMENT

To assure smooth engine operation during the after-start period the CIS-E control unit will richen the fuel mixture by increasing the current to the differential pressure regulator. The amount of enrichment is dependent on engine coolant temperature, and lasts from 30 to 50 seconds.
The control unit continues with fuel enrichment during the warm-up period based on coolant temperature. Warm-up enrichment continues, however, at a lower level than after-start enrichment and discontinues when the engine reaches normal operating temperature.

Acceleration Enrichment Graph:

COLD ACCELERATION ENRICHMENT

The CIS-E control unit increases current to the differential pressure regulator briefly when the engine is below normal operating temperature and the throttle valve is opened suddenly. This ensures good throttle response and the elimination of the familiar "flat spot" upon cold acceleration. The enrichment amount depends upon engine coolant temperature, position and movement speed of the air flow sensor plate (via the air flow sensor plate potentiometer), and engine RPM. Because of the resistance curve of the potentiometer, more enrichment will occur at low engine speeds and less at high engine speeds.

FULL THROTTLE ENRICHMENT

Full throttle enrichment guarantees maximum power output during high engine speeds.
At engine speeds above 4000 RPM the CIS-E control unit supplies additional current to the differential pressure regulator, (approx. 3 mA above the basic adjustment). Full throttle enrichment occurs only after the engine has attained normal operating temperatures.

Deceleration Fuel Shut-Off:

DECELERATION FUEL SHUT-OFF

Fuel deceleration shut-off increases fuel economy and aids in reducing exhaust emissions.
During engine deceleration, the CIS-E control unit reverses the current to the differential pressure regulator to approx. -40 mA. This raises pressure below the differential pressure valves so as to effectively shut off fuel to the injectors.
In order to accomplish smooth operation, the point at which fuel shut-off begins and ends, is dependent on coolant temperature. If the engine has attained normal operating temperatures, fuel shut-off will occur when the engine speed is above approx. 1600 RPM and the throttle valve idle switch is closed. Current flow to the differential pressure regulator will return to normal when the engine speed drops below approx. 1300 RPM, restarting injection.

Idle Stabilizer Valve:

IDLE STABILIZATION CONTROL

The idle speed is electronically controlled by the CIS-E control unit with relation to engine coolant temperature and load signals.
If the control unit recognizes that the idle speed is not within specified ranges, approx. 800-900, the duty cycle to each of the two windings in the idle stabilizer valve will be changed. This repositions the rotary valve to allow more or less air to bypass the throttle valve as necessary to maintain the correct idle speed.