Fuel Inj - Mpi System Mitsubishi Galant V

DESCRIPTION

The Multi-Point Injection system (MPI) is a computerized emission and fuel control system. The MPI system controls fuel delivery, ignition timing and idle speed. The system is designed to lower exhaust emissions while maintaining good driveability.

The Electronic Control Unit (ECU) is organizer of the MPI system. The ECU determines at which point each injector supplies fuel. The ECU also controls many of the fuel and ignition related systems to constantly adjust engine operation.

OPERATION

The MPI system is designed to maintain ideal air/fuel ratio under all operating conditions. When an ideal ratio is maintained, the vehicle operates at a higher level of efficiency. This reduces the amount of unburned fuel so the catalytic converter can better control emissions. The MPI system consists of multiple subsystems. (Scheme 9)

Multi-Point Injection System Circuit Diagram. Scheme 9

FUEL CONTROL

Fuel control system consists of an electric fuel pump, control relay, fuel filter, injectors, pressure regulator and airflow sensor. Engine fuel is supplied through 4 electronically pulsed (timed) injector valves located in the delivery pipe. The ECU controls amount of fuel metered through injectors based on engine demand information received from the sensors. (Scheme 13)

DATA SENSORS

Each sensor furnishes electrical impulses to the ECU. From this input, the ECU computes fuel delivery and spark timing necessary to maintain desired air/fuel mixture. (Scheme 13) This controls amount of fuel delivered to engine. Data sensors are interrelated to each other. Their operation is as follows

Airflow Sensor

Airflow sensor, mounted inside the air cleaner assembly, is designed to generate ultrasonic waves that are transmitted across the flow of air at a rate proportionate to rate of airflow. These waves are detected by the built-in modulator and converted to electric pulse to send a proportionate electrical signal to the ECU. (Scheme 10)

Multi-Point Injection Airflow Sensor. Scheme 10

Coolant Temperature Sensor (CTS)

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

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 idle speed.

Idle Position Switch

The Idle Position Switch (IPS) is mounted on the throttle body. (Scheme 16) When throttle valve is closed, 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 idle speed. This switch is also used as an idle speed adjusting device.

Intake Air Temperature Sensor

The Intake Air Temperature Sensor is mounted inside the air cleaner. (Scheme 10) This 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. The intake air temperature sensor has been installed to obtain optimum air/fuel mixture according to intake air temperatures when engine is operating under high load.

MPI System Components. Scheme 11

Oxygen Sensor

The oxygen sensor is a zirconia sensor located the exhaust system in front of the 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.

Cross Sectional View of O2 Sensor The O2 sensor connector lead is not to scale. Scheme 12

Pressure Sensor

The pressure sensor is integral with the ECU. This sensor provides continuous information regarding air pressure fluctuation to the ECU. The ECU uses this information in controlling air/fuel mixture.

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 13)

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 is also used to inform the ECU of altitude for system compensation. The ECU calculates air/fuel ratio necessary for engine operation in high altitude areas.

MPI System Data Processing. Scheme 13

Throttle Position Sensor

The Throttle Position Sensor (TPS) is a rotary meter attached to the throttle body. (Scheme 16) The sensor signals ECU of changes in throttle valve position. This information is used to control idle speed and fuel delivery time.

ELECTRONIC CONTROL UNIT (ECU)

The ECU is a printed circuit board enclosed in a metal housing. The ECU receives various signals from data sensors and switches. These signals are processed by the ECU for controlling fuel delivery. (Scheme 13)

The ECU monitors various engine and vehicle operations to compute fuel delivery time. 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 specific period of time.

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 for controlling fuel delivery. 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.

Electronic Control Unit Terminal Identification. Scheme 14

EGR System

The primary function of the EGR system is to reduce oxides of nitrogen (NOx) from exhaust gases. Exhaust gas is partially recirculated from an exhaust port in cylinder head through an intake manifold port. The EGR system is self regulated and consists of an EGR control valve, vacuum regulator valve, and a thermo valve.

The vacuum signal to the EGR valve is distributed through the vacuum regulator valve. the regulator valve controls the vacuum signal by a variable air bleed within the valve. The regulator valve is balanced between exhaust pressure and venturi vacuum. As internal pressure exceed preset values, regulator will utilize air bleed to assign a balanced signal to EGR valve for regulated response. The EGR flow is suspended during engine idle and wide open throttle operation.

TESTING & DIAGNOSIS

PRETESTING INSPECTION

If MPI system components fail, interruption of fuel supply or failure to supply proper amount of fuel for engine operation will result. The engine may be hard to start or not start at all. Unstable idle and/or poor driveability will be noticed. Before testing MPI system, inspect ignition system, vacuum and fuel hoses.

SELF-DIAGNOSIS

The Self-Diagnosis system, an integral part of the computer (ECU), monitors all input signals from each sensor. If an abnormal input signal occurs, that item is memorized by the computer (ECU). There are 8 diagnostic codes including normal operating condition. They can be confirmed by using a voltmeter and the diagnostic connector. (Scheme 14)

The abnormal diagnosis items are listed in the following table. If 2 or more systems are non-functional, they are indicated by order of increasing code number. Indication is made by deflection of voltmeter pointer or ECI checker. A constant 12 volts indicates system is normal. If system is abnormal, voltmeter will alternate between 0 and 12 volts to indicate trouble code.

The ECU memory is kept by direct power supply from the battery. Memory is not erased by turning off ignition switch but will be erased if back-up power supply is eliminated by disconnecting battery cable or ECU unit. Memory will not be erased if power supply is returned within 10 seconds after being disconnected.

Galant Self-Diagnosis Memory Output Pattern. Scheme 15

SELF-DIAGNOSIS TEST

Note. Before battery terminals are disconnected, make sure that ignition is off. If terminals are disconnected while engine is running or ignition is on, computer system could be damaged.

1. Turn ignition switch to "OFF" position. Connect voltmeter between MPI self-diagnosis output and Ground of diagnosis connector, located in glove compartment (Scheme 15) Turn ignition switch to "ON" position and disclosure of ECU memory will begin.
2. It is very important that voltage signals be timed accurately. The signals will appear in either.5, 1.5 or 3 second intervals. All codes begin with voltmeter registering 12 volts for 3 seconds. If more than one code is stored in memory, they will be separated by the 3 second voltmeter indication.
3. All codes are revealed by a 12 volt pulse, 1.5 second duration. The time between pulses is.5 second. An example of code 5 is 12 volts for 3 seconds, zero voltage for.5 second and 12 volts 1.5 seconds. The indications of zero voltage for.5 second and 12 volts 1.5 seconds will be repeated 5 times. (Scheme 16)
4. If more than one code is stored, they will be separated by 12 volt pulses, 3 seconds in duration. If there is any abnormality in the memory, perform the necessary component repairs. Turn ignition off and disconnect battery negative ground cable for 15 seconds or more to erase ECU memory. Reconnect power supply and repeat self-diagnostics to confirm repair.

Diagnostic Connector and MPI Memory Terminal. Scheme 16

DIAGNOSTIC CODE CHART

ECI Checker And MPI Harness Connector. Scheme 17

MPI INSPECTION TEST

1. Check voltage standards of each terminal as specified in MPI SYSTEM CHECK CHARTS at the end of this article. Make sure ignition switch, vehicle operation and conditions are observed as called out in procedure.
2. Turn ignition switch to "OFF" position and remove ECU cover. Remove body side harness connectors "A" (24 poles) and "B" (13 poles) from ECU. On ECI checker, set check switch to "OFF" position and select switch to "A". Connect ECI connector by using MPI harness connector to ECU and body harness connectors. (Scheme 17)
3. Position ECI checker on front passenger seat. Check output monitor operating condition (on or off) by alternating ignition switch from "OFF" to "ON" position. Monitor operating condition should be as follows: Airflow Sensor - ON, Injector Pulse - OFF, Oxygen Sensor - OFF. Perform checks according to charts.
4. If checker reading varies from specifications, check corresponding sensor and related electrical wiring. After component repair or replacement, recheck to confirm system performance.
5. Airflow sensor and injector pulse may be inspected by output monitors as well. Set select switch to "B". Normal operation is as follows: airflow sensor and injector are always flashing with check switch at 1 through 12. Oxygen sensor is flashing at closed loop zone. The flashes will be so short that light will appear to be continuously on.
6. Set check switch of ECI checker to "OFF" position. Set ignition switch to "OFF" position. Carefully separate connectors of ECI checker from ECU and body side harness connectors. Connect body side harness connector to ECU. Install ECU cover.

Diagnostic Check Number 1 (Oxygen Sensor)

If O2 sensor change exceeds 20 seconds while in feedback range, turn ignition switch from "OFF" position to "ON" position. If trouble code is indicated, computer is normal. If trouble code is not indicated, computer operation is not normal. Check wire harness and connector, oxygen sensor and ECU.

Diagnostic Check Number 2 (Ignition Pulse Sensor)

While cranking the engine, input of ignition signal is not applied to computer for 3 seconds or more. Check wiring harness and connector, igniter and ECU.

Diagnostic Check Number 3 (Airflow Sensor)

Airflow sensor maximum output is 10 cycles per second with engine running over 500 RPM. If engine stalls, output will rise to 100 cycles per second. Check wiring harness and connector, airflow sensor and ECU.

Diagnostic Check Number 4 (Barometric Pressure Sensor)

Pressure sensor should be under 1.5 volts or over 4.5 volts while engine is idling. Check wiring harness and connector, pressure sensor and ECU.

Diagnostic Check Number 5 (Throttle Position Sensor)

Throttle position sensor should be under .2 volts or over 4 volts while engine is idling (idle switch on). Check wiring harness and connector, ISC servo and ECU.

Diagnostic Check Number 6 (ISC Motor Position Sensor)

Throttle sensor output is under .2 volts or over 4.8 volts. Check wiring harness and connector, ISC servo and ECU.

Diagnostic Check Number 7 (Coolant Temperature Sensor)

Coolant temperature sensor should be under .1 volts or over 4.5 volts. Check wiring harness and connector, water temperature sensor and ECU.

Diagnostic Check Number 8 (No. 1 Cylinder Pulse)

No. 1 Cylinder Pulse will not input when key is in the "ON" position. Check wire harness, connector and distributor TDC sensor.

OUTPUT SIGNALS WITH ECI CHECKER IN POSITION "B" (GREEN CONNECTOR)

OUTPUT SIGNALS WITH ECI CHECKER IN POSITION "B" (WHITE CONNECTOR)

Coolant Temperature Sensor

1. Remove coolant temperature sensor from intake manifold and place end of sensor in water. Do not allow sensor to touch container. Terminal connector portion of sensor should be .12" (3 mm) above water.
2. Gradually heat water and read resistance values at terminal connectors. Resistance should be as shown in «COOLANT TEMPERATURE SENSOR RESISTANCE»(/mitsubishi/galant/v-1983-1990/remont/testing-diagnostics/#fuel-inj-mpi-system) chart. If not, replace sensor.

COOLANT TEMPERATURE SENSOR RESISTANCE

Resistor

Disconnect resistor coupler and measure resistance across power supply and each output terminal. (Scheme 17) If resistance is about 6 ohms, resistor is good. If resistance measures zero or abnormally large, resistor has short or open circuit and should be replaced.

Resistor Terminal Locations. Scheme 18

Control Relay

Control relay is mounted in engine compartment below ECU. Disconnect electrical harness and test continuity between terminal Nos. 1 and 7, then 3 and 7. (Scheme 19) If there is no continuity, relay is good. If continuity is observed, replace control relay.

Control Relay Terminal Positions. Scheme 19

Idle Switch

1. Turn ignition switch to "OFF" position. Disconnect ISC servo connector. Check for continuity between pole 2 and injection mixer body.
2. If continuity exists when throttle valve is placed in idle position and continuity exists when throttle valve is open (so that lever leaves idle switch), switch is good.
3. If continuity exists when throttle valve is in both positions, contacts are bound together. If no continuity exists when throttle valve is in both positions, grounding is defective. Replace ISC servo assembly.

ISC Servo

1. Connect voltmeter between terminals No. 1 and 4. Disconnect ISC servo connector. Turn ignition switch to "OFF" position then to "ON" position. While keeping ignition on for at least 15 seconds, check voltmeter reading.
2. Voltmeter should read 1.5 volts with ignition switch on. If after 15 seconds, needle indicates .9 volts, ISC servo and position switch are operating normally. Turn ignition switch to "OFF" position 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. Reconnect ISC servo connector. Attach a voltmeter to terminals No. 1 and 4. After the ignition is turned on, voltmeter should read 1.5 volts for 15 seconds. After 15 seconds, voltmeter reading should drop to .9 volts.
3. 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.

Switch Location and Terminal Identification. Scheme 20

1. Turn ignition switch to "OFF" position. Disconnect Throttle Position Sensor (TPS) connector. Check resistance across poles No. 1 and 2. Total resistance should measure 4 to 6 ohms.
2. Attach circuit tester to pole 3 and poles 1 and 2 individually. (Scheme 20) As the throttle valve is slowly operated from closed to wide open throttle, watch meter. Ohmmeter should show a smooth transition of resistance value.

IDLE SPEED CONTROL SYSTEM

1. Run engine at fast idle until coolant temperature is 185-205°F (85-90°C). Turn off engine. Disconnect accelerator cable from throttle lever of injection mixer. Loosen the 2 screws installing the throttle position sensor. Turn throttle position sensor fully clockwise. Tighten screws.
2. Turn ignition switch to the "ON" position for more than 15 seconds, then turn ignition off. This will set ISC servo to specified position. Disconnect ISC servo harness connector. Start engine. Check engine speed and adjust to specification with screw.
3. Stop engine. To read output voltage of TPS, insert test probe from rubber cap side of TPS connector and bring it into contact with connector pins. Insert test probes along "GW" lead (TPS output) and "B" lead (ground) of body side harness. (Scheme 20)
4. Turn ignition switch to "ON" position without starting engine. Read TPS output voltage. Output voltage should be.45-.51 volts. If not, loosen TPS mounting screws and turn sensor until correct output voltage is obtained.
5. Immediately open throttle valve, return to original position and check for proper output voltage. Readjust sensor if necessary. Remove adapter, voltmeter and test probes and reconnect ISC servo harness connector.
6. Make sure idle speed is normal. Stop engine and turn ignition switch from "OFF" position to "ON" position and after 15 seconds back to "OFF" position. Connect accelerator cable to throttle lever of injection mixer and adjust accelerator cable.

MPI System Wiring Diagram. Scheme 21

See also:
• COOLANT TEMPERATURE SENSOR RESISTANCE