Fuel Injection System - Mitsubishi Mitsubishi Starion I

DESCRIPTION

Electronically Controlled Injection (ECI) is a computerized emission, ignition and fuel control system. The ECI system adjusts engine operation to lower exhaust emissions while maintaining efficient driveability. The Electronic Control Unit (ECU) is the foundation of the ECI system. The ECU controls many of the related systems to continuously adjust engine operation.

Note. Primary sub-systems which affect operation of the fuel system will be covered in this article. Because of the interrelated functions of the computor control system (ECU), refer to ELECTRONIC CONTROL INJECTION (ECI) SYSTEM article in COMPUTER CONTROLS section for more information.

ECI System (Cordia & Mirage). Scheme 24

ECI System (Starion - Intercooled Turbo). Scheme 25

FUEL SUPPLY

Fuel supply system consists of an electric fuel pump, control relay, fuel filter, injectors, fuel pressure regulator and fuel lines. Fuel is supplied to engine through 2 electronically pulsed (timed) injector valves located in fuel injection mixer above intake manifold. The ECU controls amount of fuel metered through injectors based upon engine demand information received from data sensor signals.

Sectional View of Fuel Injector. Scheme 26

FUEL INJECTION MIXER

The fuel injection mixer uses fuel injectors and a throttle valve to control air/fuel mixture flow. In addition to these components, the mixing body also houses the fuel pressure regulator, ISC servo assembly, pulsation damper and throttle position sensor.

Intake air is drawn through the mixing body, past fuel injectors where air/fuel mixing begins. The throttle body, attached between mixing body and intake manifold, determines air/fuel flow according to throttle position.

The amount of fuel delivered by injectors is dependent upon the time that injector valve is held open by ECU. Fuel delivery time is modified by ECU to provide proper amount of fuel for all engine operating conditions.

Sectional View of Fuel Injection Mixer. Scheme 27

FUEL PRESSURE REGULATOR

The fuel pressure regulator is mounted on the fuel injection mixer. Fuel flows from top of fuel injectors to pressure regulator. The regulator is a diaphragm-operated relief valve with pressure constantly applied.

The pressure regulator maintains a constant pressure drop across injectors throughout all engine operating conditions.

ELECTRONIC CONTROL UNIT (ECU)

The ECU consists of a printed circuit board enclosed in a metal box. The ECU receives various signals from data sensors and switches. These signals are processed by the ECU for controlling fuel delivery.

The amount of fuel delivered is determined by the time that injectors are open, because the fuel pressure regulator maintains a constant pressure drop across injectors. The frequency and duration of injection (fuel delivery time) is controlled by ECU.

The ECU monitors the various engine and vehicle operations and computes the fuel delivery time. The fuel delivery time is modified for such operating conditions as engine cranking, cold starting, altitude, acceleration and deceleration.

When ignition switch is turned to "START" position, ECU calculates fuel delivery based primarily upon coolant temperature and throttle position. ECU sends an electrical signal to injectors to provide fuel for prescribed period of time. After ignition switch is released from "START" position and engine speed is above a specified RPM, ECU changes enrichment signal.

Immediately after engine starts, the ECU issues electrical signals to injectors to provide stable combustion. During engine warm-up, the ECU monitors all data sensor information and provides a richer mixture until coolant temperature reaches a preset value.

When coolant temperature exceeds preset value, ECU processes other data sensor information and issues appropriate electrical signals to injectors. This period of time is referred to as open loop mode of operation. The ECU controls fuel delivery based upon open loop programmed information until the oxygen sensor is warm enough to send modifying signals to ECU.

When the oxygen sensor is warm enough, the ECU accepts oxygen sensor information and uses it for controlling fuel delivery. When the ECU is accepting oxygen sensor information, this is referred to as closed loop mode of operation.

During closed loop operation, the ECU stores the mean values of feedback signals used to maintain optimum air fuel ratio. During open loop operation, the ECU uses these mean values to modify pre-programmed information. By doing this, the ECU can more closely control exhaust emissions even when engine is in open loop mode of operation.

DATA SENSORS

Each sensor furnishes electrical impulses to ECU. The ECU computes fuel delivery and spark timing necessary to maintain desired air/fuel mixture, thus controlling amount of fuel delivered to engine. Data sensors are interrelated to each other. Operation of each sensor is as follows

Airflow Sensor

This sensor is mounted in air cleaner assembly. (Scheme 28) The sensor measures airflow rate through the air cleaner and sends a proportionate electrical signal to ECU. The ECU uses airflow sensor information for controlling fuel delivery and secondary air management.

On Starion intercooled models, an atmospheric pressure pick-up nipple (leading to atmospheric pressure switching solenoid valve) has been added to air cleaner. Locations of oil separator and breather nipple have been changed.

Air Cleaner & Airflow Sensor Assembly. Scheme 28

Coolant Temperature Sensor (CTS)

The coolant temperature sensor is a thermistor which converts temperature of engine coolant to electrical signal for use by ECU. The ECU uses coolant temperature information for controlling fuel delivery time, EGR and air injection system.

Detonation Sensor

The detonation sensor (knock sensor) is located in cylinder block. This sensor converts engine vibration (knock) into an electrical signal. This signal is processed by the Electronic Spark Control (ESC) ignitor and relayed to ECU for determining amount of ignition timing retard. The ECU sends a signal to ESC ignitor to modify ignition timing. Ignition timing is retarded only during period of knock. The detonation sensor is strong enough to tolerate engine vibration, but excessive external impact can damage the sensor.

Engine Speed Sensor

Engine speed signal is received from ignition coil. Electrical signals from ignition coil are sent to ECU where time between signals is used to calculate engine speed. This information is used by ECU for controlling fuel delivery time, EGR and air injection system.

Idle Position Switch

This switch is mounted on fuel injection mixer. When throttle valve is closed (idle position), the switch is activated. When throttle valve is at any other position, the switch is deactivated. This information is used by the ECU for controlling fuel delivery time (during deceleration) and air injection system. This switch is also used as an idle speed adjusting device.

Intake Air Temperature Sensor

The sensor measures temperature of incoming air and supplies air density information to the ECU. The ECU uses air temperature sensor information for controlling fuel delivery. On intercooled models, an intake air temperature sensor "B" has been installed to air intake pipe to obtain optimum air-fuel mixture according to intake air temperatures when engine is operating under high load.

Oxygen Sensor

The oxygen sensor is located in the exhaust system between turbocharger and catalytic converter. Output voltage of oxygen sensor varies with oxygen content in exhaust gas stream.

When oxygen sensor signal is being interpreted by ECU, information is used to control fuel delivery time. This is called closed loop mode of operation. When oxygen sensor signals are not being interpreted by ECU, this is open loop mode of operation.

Pressure Sensor

The solenoid valve is temporarily activated by ECU whenever ignition switch is turned to "ON" or "START" positions. When activated, the solenoid measures ambient barometric pressure from above throttle valve. Ambient barometric pressure changes due to weather and/or altitude. This information is sent to ECU for controlling fuel delivery time. (Scheme 29)

After a predetermined period of time, solenoid valve is deactivated by ECU and solenoid measures intake manifold pressure below throttle valve. The ECU compares barometric pressure to intake manifold pressure and an absolute value is used to determine fuel delivery and ignition timing.

The pressure sensor and solenoid valve are also used for altitude compensation. These components inform ECU of altitude. The ECU calculates air/fuel ratio necessary for engine operation in high altitude areas.

Pressure Sensor System Circuit Diagram. Scheme 29

Throttle Position Sensor

This sensor is mounted on fuel injection mixer. The sensor, a rotary potentiometer, signals ECU of changes in throttle valve position. This information is used for controlling idle speed and fuel delivery time.

FUEL CUT-OFF

Two different fuel cut-off systems are used to change fuel delivery rate to engine

Deceleration Fuel Cut-Off

During vehicle operation, when idle position switch is off idle position, fuel delivery is determined by ECU responding to throttle valve closing speeds.

To decrease HC emissions during vehicle deceleration, fuel delivery time is decreased by changing injection interval. When engine is operated under predetermined conditions, injection interval is changed from once every 3 pulses of airflow sensor to once every 6 pulses of airflow sensor.

Over Boost Fuel Cut-Off

This fuel cut-off system protects the engine during turbocharger operation. When the pressure sensor detects higher manifold pressure than the predetermined value stored in ECU memory, the ECU changes fuel delivery rate. When pressure value is exceeded, the fuel injectors are energized according to ignition spark timing.

ADJUSTMENTS

Note. Refer to TUNE-UP article in the TUNE-UP section.

ACCELERATOR CABLE

1. For turbocharged vehicles, keep ignition key at "ON" position for at least 15 seconds before adjustment. Confirm that accelerator inner cable has no slackness.
2. If cable shows slackness adjust as follows: loosen nut so that throttle lever is free. Check routing of accelerator cable to confirm that there are no sharp twists or bends. Use adjusting nut to make adjustment of free play to within specifications. On turbocharged vehicles, check that idle speed control switch touches the stopper after idle speed control adjustment.

ACCELERATOR CABLE FREE PLAY

TESTING

Note. ECI systems require special tools to be fully diagnosed. Some checks of individual components may be made using regular shop test equipment. Components covered in this article apply only to fuel section of system. For more complete testing of ECI system, refer to ELECTRONIC CONTROL INJECTION (ECI) SYSTEM article in the COMPUTER CONTROLS section.

1. Set ignition switch to "OFF" position. Disconnect secondary wire of ignition coil. Remove air intake pipe from port on injection mixer to make visual inspection of injection status.
2. Turn ignition switch to "START" position while observing injection operation. Return ignition switch to "OFF" position and verify that fuel does not leak from injector nozzles.
3. Injection should occur when ignition is turned on and leakage should not take place with ignition off. Reconnect secondary wire to ignition coil.

INJECTOR COIL

Set ignition switch to "OFF" position. Disconnect connectors from injectors. Check injector coil for continuity with circuit tester. Resistance should read 2-3 ohms. If resistance is zero ohms or abnormally large, a short or open circuit exists in coil. Replace injector and reconnect connectors to injectors.

Switch Location & Terminal Identification. Scheme 30

ISC Servo

1. Connect voltmeter between terminal No. 3 and injection mixer body. Do not disconnect ISC servo connector. Turn ignition switch from the "OFF" position to the "ON" position. While keeping ignition on for at least 15 seconds, check voltmeter reading.
2. With ignition switch on, voltmeter should read 11-13 volts. After momentary indication of one volt, needle should stabilize at 6-13 volts. This indicates ISC servo and position switch are operating normally. Turn ignition switch to "OFF" to remove voltmeter.

ISC Servo Motor

1. Turn ignition switch to "OFF" position. Disconnect ISC servo connector. Check motor coil continuity between terminals No. 1 and 4. Resistance should read between 7 and 10 ohms. If resistance is zero ohms or abnormally large, open or short circuit exists in in motor coil. Replace ISC servo assembly.
2. Make sure there is no continuity between terminals No. 1 or 4 and injection mixer body. If continuity exists, there is a short circuit in coil. Replace ISC servo assembly.

1. Turn ignition switch to "OFF" position. Disconnect Throttle Position Sensor (TPS) connector. Check resistance across poles Nos. 2 and 3.
2. As the throttle valve is slowly operated from closed to wide open throttle, watch meter. Resistance values should make a smooth transition from 500 ohms at closed throttle to 3000-6500 ohms in fully open position.

Fuel Injection Mixer. Scheme 31

FUEL PUMP

1. Connect jumper wires between fuel pump check connector and ground. Check to ensure that operating sound of fuel pump can be heard. If no operating sound can be heard, check for defective wiring, connector, etc.
2. If connector and wiring are normal, disconnect fuel pump connector at pump and energize the pump. If pump still fails to operate, replace.

Testing Fuel Pump. Scheme 32

Removal

1. Disconnect negative battery cable and drain coolant. Remove water hose between injection mixer and intake manifold at injection mixer nipple. NOTE: To remove high-pressure hose, remove 2 bolts and gently pull pipe to slowly allow pressure to escape. If fuel pipe is abruptly removed, residual pressure will cause a gasoline spill.
2. Remove air intake pipe from injection mixer. Disconnect throttle cable from lever at injection mixer. Remove vacuum hoses at nipple of injection mixer. Disconnect harness connectors at the injectors.
3. Remove ISC servo and throttle position sensor connectors. Disconnect fuel inlet pipe and fuel return hose from injection mixer. Remove 4 bolts and separate injection mixer from intake manifold. NOTE: Loosening of cross-recessed screws requires use a cross-bladed screwdriver of the proper size.
4. Do not remove or disassemble fuel return nipple, ISC servo assembly, throttle valve, or screens in injector holder. Do not clean the following parts in solvent: throttle position sensor (TPS), variable resister, ISC servo.

Installation

1. Clean both gasket surfaces of injection mixer and intake manifold. Install new gasket and injection mixer assembly on intake manifold and tighten mounting bolts to specification.
2. Install new "O" ring into groove of high-pressure hose and connect hose to injection mixer. Firmly tighten high-pressure hose mounting bolts. Connect fuel return hose to nipple of fuel pressure regulator and set hose clamp.
3. Connect all harness connectors to injector connectors, ISC servo and sensors. Connect vacuum hoses to nipples "A", "D", "E" and "M" of injection mixer. Connect water hose to nipple of injection mixer.
4. Install air intake pipe. Refill cooling system and connect ground cable to battery. Adjust ISC servo and throttle position sensor settings. Connect accelerator cable to throttle lever of injection mixer and adjust accelerator free play. Run engine and check for fuel or water leaks.

Disassembly

1. Remove throttle position sensor. Remove hose from fuel pressure regulator and mixing body. Remove injector retainer adjusting screws to remove retainer and fuel pressure regulator.
2. Remove pulsation damper cover from retainer and pull out spring with diaphram. (Scheme 33) Gently extract injectors from mixing body and remove gaskets.
3. Remove damper and throttle return springs with connector bracket. Remove ISC servo mounting bracket and ISC servo. Remove 2 screws from mixing body. Remove mixing body and seal ring from throttle body.

Removing Pulsation Damper. Scheme 33

Cleaning

1. Clean all parts but do not immerse the following in solvent: throttle position sensor, variable resistor or ISC servo. Immersing these parts will damage the insulation. Wipe these parts with a cloth only.
2. To clean injectors and fuel pressure regulator, seal fuel inlet and outlet with sealing tape and clean in solvent. Check vacuum port of passage for clogging. Clean vacuum passage and fuel passage with compressed air.

Scheme 34

Scheme 35

1. Install new seal ring into groove of throttle body. Install mixing body onto throttle body. Install ISC servo and bracket. Install connector bracket to throttle body and clamp ISC connector into bracket. Install damper and throttle return springs.
2. Insert new seal rings (flat side up) into mixing body. (Scheme 34) Install new "O" ring onto injectors. Install injectors into mixing body, pushing injector down firmly with finger. Injectors have identification marks stamped on the body. See INJECTOR IDENTIFICATION TABLE. INJECTOR IDENTIFICATION Application Injector Code Mirage B Starion H Cordia & Tredia L (Scheme 34): Installing Seal Rings
3. Insert pulsation damper diaphram into injector retainer. Install pulsation damper spring and cover and tighten screws. (Scheme 35) Install new "O" rings onto fuel pressure regulator and position unit onto injector retainer. Check retainer filters for obstruction or damage and replace if necessary. Install injector retainer and push down firmly. Gradually and alternately tighten screws to specification. (Scheme 35): Assembling Pulsation Damper
4. Insert joint "A" of throttle position sensor (TPS) to joint "B" and temporarily tighten screws. (Scheme 36) After installing injection mixer assembly to engine, adjust throttle position sensor. Clamp connector into bracket.
5. Check for proper installation of throttle position sensor. Measure resistance value between terminals No. 1 and 2 or 2 and 3 (1 and 2 or 3 and 4 on Cordia/Tredia) while moving throttle lever from open to close. (Scheme 29) If resistance value changes as throttle lever is moved, TPS is properly installed.

Installing Throttle Position Sensor. Scheme 36

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

ECI System Wiring Diagram (Cordia & Tredia). Scheme 37

ECI System Wiring Diagram (Mirage). Scheme 38

ECI System Wiring Diagram (Starion Intercooled Models). Scheme 39