Fuel Injection System - Multi-Point Dodge Dakota Shelby

DESCRIPTION

The Chrysler Multi-Point Electronic Fuel Injection system is a computer controlled system with a separate fuel injector for each cylinder. Fuel is supplied to the engine through electronically controlled injectors located in the intake manifold. A Single Module Engine Controller (SMEC) supplies power to the injectors and determines the length of time the injectors are left open.

The SMEC is a pre-programmed computer that controls ignition timing, emission control devices and idle speed in addition to air/fuel ratio. The amount of fuel to be metered through the injector is based on engine operating condition information as supplied by various engine sensors and switches. These include the Manifold Absolute Pressure (MAP) sensor, Throttle Position Sensor (TPS), oxygen sensor, coolant temperature sensor and vehicle speed sensor.

AUTOMATIC IDLE SPEED MOTOR (AIS)

The automatic idle speed motor is operated by the SMEC. The AIS motor controls the flow of air through the throttle body during engine idle. The motor opens and closes an air by-pass on the back of the throttle body to increase or decrease idle speed as engine load varies. The SMEC monitors the AIS motor and issues a change command to the injectors to increase or decrease the amount of fuel injected. (Scheme 26)

AUTO SHUTDOWN (ASD) RELAY

Power to the fuel pump is supplied through the Auto Shutdown (ASD) relay and the SMEC. The ASD interrupts power to the fuel pump when the ignition switch is in "RUN" position and no distributor signal is present. When the SMEC receives a signal from the distributor during engine cranking, it grounds ASD relay, closing the contacts. When contacts are closed, power is applied to fuel pump. When distributor signal is lost, the SMEC opens the ASD relay, which cuts power supply to fuel pump, fuel injectors and ignition coil. This prevents fuel flow should the vehicle be involved in an accident or if engine stalls. (Scheme 21)

Scheme 21

BAROMETRIC PRESSURE SOLENOID (2.5L)

The barometric pressure read solenoid is controlled by the SMEC. The solenoid is in the MAP sensor vacuum line, next to the MAP sensor. The solenoid controls whether manifold pressure or atmospheric pressure is supplied to the MAP sensor. (Scheme 24)

CANISTER PURGE SOLENOID

The canister purge solenoid is located in the engine compartment above the rear of the right headlight. Canister purge solenoid is controlled by SMEC. When engine operating temperature is below 150°F (66°C), SMEC grounds the canister purge solenoid. This prevents vacuum from reaching the charcoal canister valve. When temperature reaches or exceeds the given value, canister purge solenoid is de-energized and vacuum is allowed to flow to charcoal canister valve. Normal purging of fuel vapors to throttle body is then allowed to continue. (Scheme 22)

Scheme 22

COOLANT TEMPERATURE SENSOR

The coolant temperature sensor, mounted in thermostat housing, measures temperature of engine coolant. This information allows the SMEC to demand slightly richer air/fuel mixtures and higher idle speeds during cold engine operation. During warm engine operation, the sensor provides data for proper radiator cooling fan operation.

DETONATION SENSOR (2.5L)

The detonation sensor is mounted on intake manifold. The vibrations created from combustion chamber detonation are detected by the sensor and converted into electrical signals and sent to the SMEC. The SMEC will adjust spark advance and/or boost as needed.

FUEL DELIVERY

Fuel is drawn from the fuel tank through a filter sock on one end of the fuel pump and is pumped out the opposite end. Two check valves are used. One relieves internal fuel pump pressure and regulates maximum fuel pressure output. The other check valve, located near pump outlet, restricts fuel flow in either direction when pump is not running. Power is supplied to the fuel pump through the Auto Shutdown (ASD). Fuel not used by the engine is returned to the tank by a fuel return line. (Scheme 23)

Scheme 23

FUEL INJECTORS

The fuel injectors are an electric solenoid, powered and controlled by the SMEC. The SMEC determines when and how long the injector should operate. When electric current is supplied to the injector, the armature and pintle move a short distance against a spring, opening a small orifice. Since fuel is under high pressure, a fine spray is developed and injected into the intake manifold where it is further atomized before being drawn into the combustion chamber.

MANIFOLD ABSOLUTE PRESSURE (MAP)

The MAP sensor, mounted on the firewall for 2.5L turbo and mounted on the alternator bracket for 3.0L applications, monitors manifold vacuum via vacuum line attached to throttle body. The MAP sensor supplies the SMEC with an electrical signal which indicates manifold vacuum and barometric pressure. This information helps to determine air/fuel ratio. (Scheme 24)

Scheme 24

OXYGEN SENSOR

Oxygen sensor is mounted in exhaust manifold or turbo outlet. The oxygen sensor monitors oxygen content of exhaust gases and generates voltage signals proportional to oxygen content.

Voltage signal to the SMEC is low when oxygen content of exhaust gases is high, indicating lean air/fuel mixture. If oxygen content decreases (mixture becomes richer), signal voltage will increase.

SINGLE MODULE ENGINE CONTROLLER (SMEC)

The SMEC contains the necessary circuits to drive ignition coil, fuel injectors and alternator field. It contains a 14-pin connector and a 60-pin connector. The SMEC is a digital computer containing microprocessors. It receives input signals from various switches and sensors.

The SMEC then computes the fuel injector pulse width, spark advance, ignition coil dwell, idle speed, purge, cooling fan start and alternator charge rate. The SMEC contains voltage converters which convert battery voltage to 9 volt output. The SMEC is located on the right inner fender panel. (Scheme 21)

Note. For more information on the SMEC, see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

THROTTLE POSITION SENSOR (TPS)

The TPS is a variable resistor which is activated by throttle shaft movement. It is mounted on the throttle body and senses angle of throttle blade opening. A voltage signal is produced by the sensor which varies with this angle. This signal is transmitted to the SMEC where it is used to adjust air/fuel ratio during acceleration, deceleration, idle, and wide open throttle.

WASTEGATE CONTROL SOLENOID (2.5L)

The wastegate control solenoid is located in the engine compartment above the rear of the right headlight. (Scheme 22) Maximum turbocharger boost is controlled by the SMEC, which changes duty cycle of wastegate solenoid. Boost is then varied to operating conditions.

PRELIMINARY CHECKS

Most driveability problems in the multi-point fuel injection system are the result of faulty wiring or loose and/or leaking hose connections. To avoid unnecessary testing, check the following before beginning trouble shooting procedures. A preliminary visual check should include

1. Air ducts at air cleaner, turbocharger and throttle body.
2. All electrical connections at components.

Check vacuum lines for tight, leak-free connections in these areas

1. MAP sensor.
2. PCV valve to turbocharger vacuum port.
3. Solenoid bank.
4. Throttle body.
5. Vapor canister.

Ensure the following electrical connectors are properly attached

1. 14-pin and 60-pin connector at SMEC.
2. ASD relay connections.
3. Detonation sensor connections.
4. Coolant temperature sensor connector.
5. Distributor connectors.
6. Fuel injector connectors.
7. Radiator fan relay connectors.
8. O2 sensor connector.
9. Speed sensor connector.
10. Throttle body connector.

Fuel System Pressure Test

1. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under REMOVAL & INSTALLATION in this article. Remove cover from service valve on fuel rail (if equipped). Connect Fuel Pressure Gauge (C-3292) and Adapter Hose (C-4799) to service valve. Connect Diagnostic Readout Box II (DRB-II). Turn ignition on.
2. Use Actuate Outputs Test "Auto Shutdown Relay" on DRB-II to activate fuel pump. Check reading on testers after system is pressurized. Correct pressure reading should be 55 psi (3.9 kg/cm 2 ) for turbo models and 48 psi (3.3 kg/cm 2 ) for 3.0L models. If pressure is high, proceed to step 4). If pressure is low, relocate tester to fuel supply line between fuel filter and fuel tank.
3. Repeat test and check reading on testers after system is pressurized. If pressure rises about 5 psi (.37 kg/cm 2 ), replace fuel filter. If not, lightly squeeze return hose. If pressure increases, replace pressure regulator. If no change occurs, inspect fuel filter and filter sock for restriction or malfunction.
4. If pressure was high in step 2) remove fuel return line from fitting at fuel tank. Attach a 36" piece of fuel hose to fuel return line with the opposite end in an approved gasoline container. Repeat test with fuel flowing into container. If pressure is now correct, check in-tank return hose, resevior check valve and aspirator jet for binding or restriction.
5. If pressure remains high, remove return hose from fuel pressure regulator. Attach a piece of fuel hose to fuel pressure return line with the opposite end in an approved gasoline container. Repeat test and check reading on testers after system is pressurized. If pressure is now correct, check for restricted fuel return line. If pressure remains high, replace fuel pressure regulator.

SYSTEM DIAGNOSIS

The multi-point fuel injection system is part of the computerized engine controls system. This system is equipped with "On-Board Diagnostics," which has a self-diagnostic capability that checks several circuits.

If abnormal signals occur often enough to indicate a valid problem, the SMEC will store the fault code for later display. If problem is either repaired or disappears by itself, the SMEC will remove the fault code after 50-100 engine starts.

When a fault code is set, the "Check Engine Light" comes on. Located on instrument panel, this light informs operator that malfunction in system has occurred and immediate service is required.

The SMEC will attempt to compensate for failure of a component by using input from remaining sensors. If the "Check Engine Light" comes on or certain driveability and engine performance problems exist, the source of these difficulties may be determined by displaying and recording fault codes. Check FAULT CODES to determine questionable circuit.

FAULT CODES

Note. For fault codes and code descriptions, see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

PRECAUTIONS

Before removing any fuel system components, system pressure must be relieved. See FUEL SYSTEM PRESSURE RELEASE under REMOVAL & INSTALLATION in this article. It is not necessary to remove throttle body from intake manifold to remove components.

If any components such as hoses or clamps are replaced, ensure they are replaced with components designed for EFI use. Always reassemble throttle body components with new "O" rings and seals.

FUEL SYSTEM PRESSURE RELEASE

1. Fuel pressure must be fully released before opening fuel loop or removing any fuel carrying components. To release pressure in tank, open fuel tank cap slowly.
2. To release remaining pressure in system, disconnect 2-pin connector from fuel injector. Using jumper wire, connect injector harness ground terminal No. 1 to ground. Connect injector harness positive terminal No. 2 to positive battery terminal with second jumper wire. (Scheme 25)
3. DO NOT keep injector connected to positive battery terminal for longer than 5 seconds. Remove jumper wires. Fuel injection system loop can now be opened and fuel carrying components removed as pressure is fully released.

Scheme 25

Removal & Installation

Disconnect negative battery cable and throttle body wiring connector. Remove 2 screws mounting throttle position sensor to throttle body. Remove throttle position sensor from throttle shaft. To install, remove removal procedure. (Scheme 26)

1. Disconnect negative battery cable. Remove screws attaching air cleaner to throttle body. Loosen hose clamp and remove air cleaner adapter. Remove accelerator, speed control and transmission kickdown cables and return spring.
2. Remove throttle cable bracket from throttle body. Disconnect electrical connector. Disconnect vacuum hoses from throttle body. Loosen screws attaching throttle body to intake manifold. Remove throttle body. To install, reverse removal procedure.

Scheme 26

Remove air cleaner. Disconnect battery negative cable and 4-pin AIS connector. Remove temperature sending unit from throttle body housing. Remove 2 Torx screws that secure AIS. Remove AIS motor. Ensure "O" ring is removed from throttle body. To install, reverse removal procedure. Use new "O" ring. Install 2 mounting screws and tighten to 17 INCH lbs. (2 N.m).

Note. Measure exposed pintle before starting installation. If exposed pintle measures more than 1" (25 mm), reconnect battery and retract pintle. See appropriate article in COMPUTERIZED ENGINE CONTROLS section.

With fuel tank removed from vehicle, use hammer and brass punch to carefully tap lock ring counterclockwise and release pump. Remove fuel pump and "O" ring seal from tank. Discard old seal. To install, reverse removal procedure, making sure seal area is clean. Take care not to overtighten pump.

Removal

1. Release fuel system pressure. See «FUEL SYSTEM PRESSURE RELEASE»(/dodge/dakota-shelby/1989-1989/remont/testing-diagnostics/#fuel-injection-system-multi-point__fuel-system-pressure-release) under REMOVAL & INSTALLATION in this article. Disconnect negative battery cable. Remove air cleaner assembly. Disconnect detonation sensor and fuel injector wiring connectors. Loosen supply hose clamp and return hose clamp at fuel pressure regulator and remove hoses.
2. Remove fuel pressure regulator vacuum hose from regulator. Remove fuel pressure regulator-to-fuel rail attaching nuts. Remove fuel pressure regulator from fuel rail. Remove PCV vacuum harness and vacuum vapor harness from intake manifold.
3. Remove fuel rail to valve cover bracket screw. Disconnect detonation sensor connector. Remove fuel rail-to-intake manifold attaching screws. Remove fuel rail and injector assembly so injectors come straight out of ports. Use care to not damage "O" rings. Remove fuel rail assembly from vehicle.
4. Cover injector ports with a rag while injectors are serviced. DO NOT remove fuel injectors until fuel rail assembly has been removed from vehicle.

Installation

1. Seat injectors in cups (if removed) and install lock rings. Ensure injector holes are clean. Lube injector "O" rings with drop of oil. Install injector assemblies in sockets. Install 2 attaching bolts and ground straps. Tighten bolts to pull fuel rail into place evenly with each injector in its own hole.
2. To complete installation, reverse removal procedure. All wiring, hoses and ground straps must be in original positions. Use ATM tester or start vehicle to check for fuel leaks.

Remove injector wiring connector from injector. Position fuel rail assembly so fuel injectors are accessible. Remove injector lock ring from fuel rail and injector. Pull injector straight out of fuel rail receiver cup.

Inspection

Check injector "O" ring for damage. If injector is to be reused, install a protective cap over the injector tip to prevent damage.

Lightly lubricate injector "O" ring with engine oil before installation. Install injector top end into fuel rail cup. Use care not to damage "O" ring during installation. Install injector lock ring. To complete installation, reverse removal procedure.

1. Perform fuel system pressure release procedure. Disconnect negative battery cable. Remove vacuum hose from fuel pressure regulator. Loosen fuel return hose clamp at fuel pressure regulator and remove hose. Wrap a rag around hose to collect fuel spillage.
2. Remove fuel pressure regulator attaching nuts. Remove fuel pressure regulator from rail. Before installation of regulator, lubricate "O" ring. To install, reverse removal procedure.

Remove air cleaner duct from SMEC. Remove battery. Remove mounting screws and electrical connectors. To install, reverse removal procedure. (Scheme 21)

Using Sensor Socket (C-4907), remove oxygen sensor from exhaust manifold. Using 18 mm x 1.5 x 6E tap, clean threads in exhaust manifold. New oxygen sensors come with anti-seize on threads. If old sensor is to be reused, coat threads with anti-seize compound. Tighten oxygen sensor to 20 ft. lbs. (27 N.m).

WIRING DIAGRAMS

Note. For wiring diagrams, see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

See also:
• FUEL SYSTEM PRESSURE RELEASE