DESCRIPTION
The feedback carburetor design provides the ability to accurately control air/fuel mixtures using closed loop control. The secondary air system, throttle opener system and deceleration spark control system are also controlled to reduce exhaust emissions.
A/C CONTROL
In response to performance demands, ECU will shut off A/C compressor at or above a preset throttle opening.
AIR INJECTION CONTROL
A solenoid is used to direct the air control valve signal vacuum. The solenoid is controlled by the ECU based on engine speed, idle position and coolant temperature. The control valve routes air to the exhaust manifold.
DECELERATION SPARK CONTROL
Ignition timing is advanced by the solenoid operated vacuum valve on the distributor to decrease hydrocarbon (HC) emissions during vehicle deceleration. Vacuum supplied to the valve is changed from the carburetor ported vacuum to intake manifold vacuum. The solenoid valve is controlled by ECU based on engine speed.
ENRICHMENT SYSTEM
The enrichment system consists of a metering jet and solenoid-operated enrichment on-off valve. Valve provides additional fuel for main metering system. When additional fuel is required during acceleration, heavy engine loads, cold start or warm-up operation, the ECU energizes the solenoid at pre-set duty cycles.
Input signals from a variety of sensors are fed into the electronic control unit (ECU). The ECU then generates output signals for controlled fuel and spark timing performance. Air/fuel mixture is controlled by varying the amount of time the solenoid is energized during each cycle. The ECU monitors throttle position, engine speed, coolant temperature, intake air temperature and exhaust oxygen concentration to determine desired air/fuel ratio.
FUEL CUT-OFF SYSTEM
As the ignition is deactivated, deceleration solenoid valve stops the fuel flow to prevent engine run-on. During deceleration, the deceleration solenoid valve reduces the fuel flow to the carburetor.
JET MIXTURE SYSTEM
Jet mixture system supplies fuel to the engine through jet mixture passages and jet valves for optimum air/fuel mixture. The system is calibrated by jet mixture solenoid which responds to electrical impulses from the ECU.
If oxygen sensor detects a lean condition, the ECU energizes the solenoid to enrich the mixture. If sensor detects a rich condition, the ECU signals the solenoid to lean out the mixture.
THROTTLE OPENER CONTROL
During air conditioner operation, engine speed is increased by changing the throttle valve opening. In order to decrease HC emissions during deceleration, ECU de-energizes solenoid valve which supplies manifold vacuum to throttle opener at or above the preset engine speed.
TESTING - CHRYSLER
| CAUTION | Be sure ignition switch is in "OFF" position when separating connectors from control unit. While testing, use caution to avoid damaging pins. Touch only one pin at a time with each lead. |
PRETESTING INSPECTION
If FBC system components fail, fuel supply could be interrupted or fail completely. The following conditions may be noticed during engine operation: engine is hard to start or does not start at all, unstable idle and/or poor driveability. Before testing FBC system, perform basic ignition system and engine adjustment inspection.
TEST PROCEDURE
Separate computer terminal connector and identify pin terminal numeration. (Scheme 11)and (Scheme 12). Use a voltmeter to measure voltage at connector terminal as outlined in the OUTPUT SIGNAL CHARTS. Be sure to verify that the vehicle conditions called for in the charts are observed. Use the charts to interpret the voltage signals to isolate malfunctioning components. Note and record the results.
TESTING - MITSUBISHI
| CAUTION | Be sure ignition is off when removing battery terminals or separating connector from control unit. If battery terminals are disconnected while engine is running, or with ignition on, damage to semi-conductors could result. |
If FBC system components fail, fuel supply will be interrupted or completely shut off. The following conditions will result: engine will be hard to start or not start at all, unstable idle and/or poor driveability. Before testing FBC system, perform basic ignition system and engine adjustment inspection. Fuel system is checked with ECI checker and FBC harness connector.
ECI CHECKER TESTING
- With ignition off, remove the harness connectors "A" and "B" from ECU. Make sure to press down on harness connector lock when connecting or disconnecting harness connector. Turn Mitsubishi ECI system checker check switch to "OFF" position.
- Set select switch of checker to "A". Connect the adapter to the connectors of ECI checker. Connect adapter to carburetor control unit and harness connectors. Place ECI checker on front passenger seat.
- Perform tests as outlined in OUTPUT SIGNAL CHARTS. If checker varies from specifications, check corresponding sensor and related electrical wiring and repair as necessary. Recheck with ECI checker.
Note. During checks 1 through 12, finish each step quickly and switch off ignition after each step to save current consumption and protect the battery.
