Fuel Injection System - Multi-Point Dodge Caravan I

COMPONENT TESTING

Note. Specific component testing information not available. Refer to tests performed under TESTING .

DESCRIPTION

The 3.0L engine with Multi-Point Fuel Injection is used on the 1987 Caravan, Mini Ram Van and Voyager. A new design Single Module Engine Controller (SMEC) is the "brain" of the system. This system combines the Power module and the Logic module in one unit. The SMEC processes all sensor inputs and assigns control signals to all output devices to control injector pulse width ("on-off" time), spark advance, idle speed, and other engine functions.

In order to control these systems, the computer monitors several engine and vehicle operating conditions. Engine speed and manifold absolute pressure are the primary signals used to control the injection signal.

Injectors are mounted in each branch of the intake manifold and spray fuel directly into each intake port. The throttle body includes an air by-pass automatic idle system, operated by a stepper motor.

The SMEC tests many of its own input and output circuits. If a fault is found in a major circuit, a memory code is stored in the system. These codes may be accessed using diagnostic readout equipment or through the instrument panel power loss light. For further information on this system, see COMPUTERIZED ENGINE CONTROLS section.

Scheme 31

OPERATION

The injection system consists of a number of primary and sub-systems which control fuel injection. These systems include Fuel Control, Data Sensors and Switches, Single Module Engine Controller (SMEC), Idle Speed Control, Fuel Injectors and Automatic Shutdown Relay.

FUEL CONTROL

An electric, positive-displacement, roller-vane type fuel pump is located in the fuel tank. The fuel pump is an integral part of the fuel gauge sending unit. The fuel pump supplies fuel to the fuel rail. A fuel pressure regulator mounted on the fuel rail maintains fuel system pressure at a constant 36 psi (2.5 kg/cm 2 ).

Power to the fuel pump is supplied by the SMEC via the Automatic Shutdown (ASD) relay. When the SMEC senses a distributor signal during cranking, it grounds the ASD closing contacts. This completes the circuit for the electric fuel pump, injectors and ignition coil. If the distributor signal is lost for any reason, the ASD relay shuts off this circuit in less than one second. This prevents fueling, spark and engine operations.

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor is located in the engine compartment, mounted on firewall. This sensor supplies the SMEC with an electrical signal that indicates manifold pressure and barometric pressure conditions. This information on engine load is combined with data supplied by other sensors to determine correct air-fuel ratio.

Heated Oxygen (O2) Sensor

The oxygen sensor is mounted in the rear exhaust manifold where it is exposed to exhaust gas flow. The sensor monitors oxygen content of exhaust gases and reacts to oxygen content by producing a proportional voltage output signal that is sent to the SMEC. The O2 sensor is equipped with a heating element that keeps the sensor at a consistent temperature under warm-up and idle conditions.

Coolant Temperature Sensor (CTS)

The CTS is a dual thermistor that measures temperature of engine coolant. The coolant temperature sensor is mounted in the thermostat housing. One side of the CTS supplies SMEC with a voltage signal that varies with engine coolant temperature. The other side of the sensor is used to control the electric cooling fan.

Charge Temperature Sensor

The charge temperature sensor measures the temperature of the incoming air/fuel mixture. The sensor, mounted in the intake manifold, supplies the SMEC with incoming air/fuel mixture temperature information.

Throttle Position Sensor (TPS)

The TPS is mounted on the throttle body and senses throttle blade opening angle. The sensor produces a voltage signal that varies with throttle 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 conditions.

SINGLE MODULE ENGINE CONTROLLER (SMEC)

The SMEC contains the operating software and performs calculations and adjustments necessary for engine operation. The SMEC is located at the front of the left fender panel in the engine compartment. The SMEC is a microprocessor-based digital computer, with 60-pin and 14-pin connectors. The SMEC receives input signals from various switches, sensors and other components. Using these signals, the microprocessor computes fuel injector pulse width, spark advance, ignition coil dwell, automatic idle speed actuation, canister purge cycle, cooling fan operation and alternator output.

The SMEC also contains a diagnostic circuit to test input and output circuits. The diagnostic circuit will store information about any malfunctions as they occur for read-out prior to service. The Chrysler Motors Diagnostic Read-Out Box (C-4805) or the flashing "CHECK ENGINE" light may be used in diagnosing and displaying trouble codes. The "CHECK ENGINE" light is limited in its diagnostic capabilities.

IDLE SPEED CONTROL

Idle speed is controlled by the SMEC through the Automatic Idle Speed (AIS) motor. The AIS is mounted on the throttle body assembly. The SMEC uses sensor input to determine optimum engine idle speed for any idle condition.

The AIS receives control signals from the SMEC to adjust the amount of air allowed through the air by-pass in the throttle body. This by-pass is enlarged or restricted, as an increase or decrease in engine idle speed is required, to meet various conditions. The SMEC uses sensor input to determine optimum engine idle speed for any idle condition.

The AIS receives control signals from the SMEC to adjust the amount of air allowed through the air by-pass in the throttle body. This by-pass is enlarged or restricted, as an increase or decrease in engine idle speed is required, to meet varying engine operating conditions. The SMEC also monitors A/C operation and transaxle lever position. When necessary, the SMEC issues commands to the AIS to increase idle speed under these load conditions.

FUEL INJECTORS

Pressurized fuel is supplied to the injectors by the fuel rail and released into the intake manifold by the solenoid valves in each injector. The signal from the SMEC controls the duration of the release. The injectors are sealed by replaceable "O" rings and are attached to the fuel rail with locking clips.

AUTOMATIC SHUTDOWN RELAY

When the ignition switch is in the "RUN" position and no ignition signal from the distributor is present, the Automatic Shut-down Relay (ASD) interrupts power to the fuel pump, injectors and ignition coil.

THROTTLE BODY

The throttle body controls air intake into the intake manifold. It is located on the Air Intake Plenum and is controlled by a cable-operated throttle butterfly plate. The throttle body incorporates the AIS motor and TPS.

PRELIMINARY CHECKS

Most driveability problems in the fuel injection system result from faulty or poor wiring, or loose and/or leaking hose connections. Electrical connections should be checked to ensure connector terminals lock together and wiring between each connector and wiring harness is not pinched or frayed in such a way as to produce a short to ground condition.

All hose and vacuum connections should be checked to ensure connectors are fully and firmly seated. Ensure hoses and lines are not pinched, melted or cut.

Ensure engine has spark at spark plugs. If no or weak spark exists, see appropriate DISTRIBUTORS & IGNITION SYSTEMS article in ELECTRICAL section.

If the "CHECK ENGINE" light comes on, or if certain drive- ability or engine performance difficulties exist, the probable source of these difficulties may be determined by entering "On-Board Diagnostics" and recording the trouble codes as they are displayed. Trouble codes may be displayed on the Chrysler Motors Diagnostic Read-Out Box (C-4805) or, to a limited extent, be flashed on the "CHECK ENGINE" light.

The SMEC has 5 different test modes. Corresponding codes are used for each diagnostic mode. All 5 test modes must be used to properly diagnose the system. For further information on this system, see COMPUTERIZED ENGINE CONTROLS section.

RELEASING FUEL PRESSURE

To release fuel pressure from fuel injection system, loosen gasoline cap to release tank pressure. Remove wiring harness connector from injector. Ground one injector terminal and touch battery positive post for no longer than 10 seconds. Remove jumper wires.

1. Disconnect negative (-) battery cable. Remove air cleaner hose at throttle body. Remove throttle cable and transaxle linkage. Disconnect AIS and TPS connectors. (Scheme 32)
2. Disconnect vacuum hoses from throttle body. Remove throttle body. To install, reverse removal procedure.

Scheme 32

Disconnect battery and TPS connector. Remove 2 mounting screws and sensor from throttle body. To install, reverse removal procedure.

Scheme 33

AUTOMATIC IDLE SPEED (AIS) MOTOR

Disconnect battery and 4-pin AIS connector. Remove mounting screws from throttle body. Remove AIS motor. Ensure "O" ring is positioned on AIS motor. To install, reverse removal procedures.

Scheme 34

FUEL INJECTOR RAIL ASSEMBLY

1. Release fuel pressure from fuel rail. Disconnect battery cable. Remove air cleaner hose, throttle cable and linkage. Remove AIS and TPS wiring connectors.
2. Disconnect vacuum lines and hoses. Disconnect EGR pipe flange from intake plenum. Disconnect temperature sensors. Remove fuel hoses from fuel rail. Remove air plenum chamber from intake manifold.
3. Protect intake manifold runners from contamination. Remove vacuum hoses from fuel rail and fuel pressure regulator. Disconnect injector wiring harness.
4. Remove fuel pressure regulator from fuel rail. Remove mounting bolts and lift fuel rail from intake manifold. Ensure "O" rings are not damaged upon removal from ports.
5. To install, ensure injectors are seated in receiver cups on fuel rail with lock ring in place. Lubricate injector "O" ring with engine oil when installing in intake manifold. Reverse removal procedure to complete installation.

Scheme 35

FUEL PRESSURE REGULATOR

Fuel pressure regulator is a non-adjustable sealed unit. Refer to FUEL INJECTOR RAIL procedure for removal and installation.

FUEL INJECTOR

Remove fuel rail assembly. Remove injector retaining clip. Pull injector straight out of fuel rail receiving cup. Ensure injector tips are protected while injectors are removed. Replace "O" ring if worn or damaged. Lubricate "O" ring prior to installation. To install, reverse removal procedure. (Scheme 35)

MANIFOLD ABSOLUTE PRESSURE (MAPS) SENSOR

Remove vacuum hose and mounting screws. Disconnect wiring connector. Reverse removal procedure to install.

Remove air cleaner duct and disconnect battery. Remove 2 module mounting screws. Disconnect wiring connectors. Remove module assembly. To install, reverse removal procedure.

Scheme 36

Scheme 37

HEATED OXYGEN SENSOR (O2)

Disconnect sensor wiring. Remove sensor using Sensor Remover/Installer (C-4907). With sensor removed, clean threads using a 18mm x 1.5mm x 6E tap. Coat threads of used sensor with anti-seize prior to installation. To install, reverse removal procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TESTING
• FUEL INJECTOR RAIL