Fuel Injection System - Tbi Dodge Caravan I

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures

DESCRIPTION

The Single-Point fuel injection system is a computer regulated fuel delivery system that provides precise air/fuel mixture during all engine operating conditions. The control unit is a Single Module Engine Controller (SMEC), that regulates ignition timing, air/fuel mixture, emission control devices, cooling fan, charging system and idle speed.

OPERATION

Fuel flow operation from the Single-Point injection system is controlled by SMEC. SMEC receives input from various sensors in order to correctly regulate fuel flow at the injector. These include the Manifold Absolute Pressure (MAP) sensor, Throttle Position Sensor (TPS), Oxygen (O2) sensor, coolant temperature sensor, throttle body temperature sensor and vehicle distance sensor. All inputs are converted into signals that are used to adjust air/fuel mixture and/or ignition timing.

A/C CUT-OUT RELAY

The A/C cut-out relay is connected in series with the A/C damped pressure switch, A/C switch and A/C fan relay. The relay remains in the energized ("ON") position during engine operation. When SMEC senses low idle speeds or wide open throttle position (through TPS), it de-energizes the relay and causes the compressor clutch to disengage.

AUTOMATIC IDLE SPEED (AIS) MOTOR

The AIS motor is operated by SMEC. SMEC uses input information from the various sensors to determine idle speed. The AIS motor meters a portion of the air/fuel mixture through an air by-pass in the throttle body. An increase or decrease in the amount of air/fuel mixture through the air by-pass is used to control idle speed.

AUTO SHUTDOWN (ASD) RELAY

The ASD interrupts power to the electric fuel pump, fuel injectors and ignition coil, when the ignition switch is in "RUN" position and no distributor signal is present.

CHECK ENGINE LIGHT

The check engine light illuminates each time the ignition is turned on, and stays on for 3 seconds as a bulb test. If SMEC receives an incorrect signal or no signal from certain sensors, the check engine light will be illumniated. This an indication that SMEC has entered into a limp-in mode. This limp-in mode is an attempt to keep the system operating despite system fault.

Scheme 27

COOLANT TEMPERATURE SENSOR

The coolant temperature sensor monitors engine operating temperature. The sensor is mounted in the thermostat housing. The coolant sensor provides data to SMEC on the engine operating temperature. SMEC uses this information to assist in determining proper air/fuel mixture at various temperatures. The sensor is also used to operate the electric cooling fan.

FUEL INJECTOR

The fuel injector is an electrically actuated solenoid that is driven or energized by SMEC. Fuel delivery is controlled by the length of time that the injector is energized. SMEC uses input signals from the various sensors to determine how long to energize the injector. Fuel is supplied to the injector at a constant pressure of 14.5 psi (1.02 kg/cm 2 ).

FUEL PRESSURE REGULATOR

The fuel pressure regulator is a mechanical device that maintains a constant pressure of 14.5 psi (1.02 kg/cm 2 ) across the injector tip. When fuel pressure reaches the given amount, fuel is allowed to enter the return port and is returned to the fuel tank. The internal diaphragm and spring constantly move from an open to closed position in order keep fuel pressure constant.

HEATED OXYGEN (O2) SENSOR

The O2 sensor produces an electrical voltage in response to the amount of oxygen in the exhaust gases. The O2 sensor is mounted in the exhaust manifold and is electrically heated internally for faster switching from open loop to closed loop operation. By monitoring the amount of oxygen in the exhaust gases the O2 sensor acts as an rich/lean switch. This is accomplished through SMEC, which reads the voltage signal from the O2 sensor and adjusts injector pulse width (on time) to maintain proper air/fuel ratio.

MANIFOLD ABSOLUTE PRESSURE (MAP)

The MAP sensor is a device that monitors manifold vacuum. The MAP sensor is connected to a vacuum nipple on the throttle body and electrically sends signals to SMEC. SMEC uses this data to determine engine load. This information is used with other data to determine proper air/fuel mixture.

PURGE SOLENOID

The purge solenoid is controlled by SMEC. When engine operating temperature is below 45°F (61°C), SMEC grounds the purge solenoid thereby energizing the component. This prevents vacuum from reaching the charcoal canister valve. When temperature reaches or exceeds the given value, the 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.

SINGLE MODULE ENGINE CONTROLLER (SMEC)

SMEC is a digital computer containing a microprocessor. The module receives input signals from various switches and sensors. After computing input data, SMEC sends output signals to the fuel injectors, distributor, ignition coil, AIS motor, purge solenoid, alternator and cooling fan switch.

SMEC contains the circuits necessary to drive the ignition coil, fuel injector and alternator field. These are high current devices and have been isolated to minimize electrical noise in the passenger compartment. Distributor pick-up signal goes to SMEC. If no distributor signal is given to SMEC, power is shut off from the fuel injector, fuel pump and ignition coil.

SMEC also performs self diagnostic functions. This diagnostic information is stored in the way of trouble codes. Trouble codes can be read by a technician by means of a diagnostic readout tool, or by means of the instrument panel check engine light.

SWITCH INPUT

Various switches provide information to SMEC. These include the neutral safety switch, A/C clutch switch, speed control switch and brake light switch. If one or more of these switches is sensed as being in the "ON" position, SMEC will signal the AIS motor to regulate idle speed at a scheduled RPM.

THROTTLE BODY

The throttle body assembly is mounted on the intake manifold and houses the fuel injector, fuel pressure regulator, TPS, AIS motor and throttle body temperature sensor. The throttle body meters air/fuel mixture delivery to intake ports. The throttle body also serves as a chamber for atomization of incoming air and fuel.

THROTTLE BODY TEMPERATURE SENSOR

The throttle body temperature sensor is used to determine fuel temperature. This sensor inputs the necessary information needed by SMEC to provide proper air/fuel mixture during hot restart conditions.

THROTTLE POSITION SENSOR (TPS)

The TPS is mounted on the throttle body and senses the angle of the throttle body valve (butterfly). This information is used by SMEC in determining proper air/fuel mixture during varying driving conditions such as; acceleration, deceleration, idle and wide open throttle.

TROUBLE SHOOTING

When a fault code is indicated (either by flashing check engine light or by diagnostic readout tool), SMEC has recognized an abnormal signal in the system. Fault codes indicate the result a failure in the fuel delivey system. The following fault codes can be set by SMEC

1. Code 88-Start of test.
2. Code 11-Engine not cranked since battery was last disconnected.
3. Code 12-Memory standby power lost.
4. Code 13-MAP sensor pneumatic circuit.
5. Code 14-MAP sensor electrical circuit.
6. Code 15-Vehicle distance sensor.
7. Code 16-Loss of battery voltage sense.
8. Code 17-Engine operating temperature too low.
9. Code 21-Oxygen sensor circuit.
10. Code 22-Coolant temperature sensor circuit.
11. Code 23-Throttle body temperature sensor circuit.
12. Code 24-Throttle position sensor circuit.
13. Code 25-AIS motor driver circuit.
14. Code 26-Peak injector current not being reached.
15. Code 27-Fuel injector control problem.
16. Code 31-Purge solenoid circuit.
17. Code 33-A/C cutout relay circuit.
18. Code 34-Speed control solenoid driver circuit.
19. Code 35-Fan control relay circuit.
20. Code 41-Charging system excess or no field circuit.
21. Code 42-Auto shutdown relay driver.
22. Code 43-Spark interface circuit.
23. Code 44-Loss of FJ2 to logic board.
24. Code 46-Battery voltage too high.
25. Code 47-Battery voltage too low.
26. Code 51-Lean condition indicated.
27. Code 52-Rich condition indicated.
28. Code 53-Internal logic module problem.
29. Code 55-End of message.

OBTAINING FAULT CODES

1. Connect Diagnostic Readout Tool (C-4805) to diagnostic connector located in engine compartment near passenger side strut tower.
2. Start engine and cycle transmission selector. Also cycle A/C switch (if equipped). Turn engine off.
3. Turn ignition on, off, on, off, on, within 5 seconds. Record all diagnostic codes displayed. Observe power loss light on instrument panel. Light should light for 3 seconds then go out. For further information on trouble codes and diagnostics see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

VISUAL INSPECTION

A visual inspection for loose or inproperly routed wires or vacuum hoses should proceed any test procedure. The following visual checks should be performed on the Single-Point fuel injection system

1. Verify that battery terminals are clean and that battery is fully charged.
2. Verify that vacuum connections on rear of throttle body are secure and not leaking.
3. Check that all vacuum connections to purge solenoid are secure and not leaking.
4. Check hoses to vapor canister.
5. Verify that PCV valve is securely attached to intake manifold vacuum port and orificed plug is in valve cover nipple.
6. Check that alternator wiring and belt are secure.
7. Check vacuum line to MAP sensor.
8. Check fuel lines to fuel pump. Verify that wiring is secure and not damaged.
9. Verify that heated air door vacuum connections are secure and not leaking.
10. Check hoses to back pressure transducer.
11. Check power brake and speed control vacuum hoses.
12. Verify that all connectors to SMEC are fully inserted into sockets. Check all other connectors to various sensors and switches.

Note. For further information on fuel system testing see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

FUEL SYSTEM PRESSURE RELEASE

Note. The fuel system is under constant pressure. Before servicing fuel system ensure that pressure is released.

1. Loosen gas cap in order to release tank pressure. Remove wiring harness connector from injector.
2. Ground one terminal of injector. Connect a jumper wire to second terminal and energize injector by touching other end of jumper to battery positive terminal. This will release system pressure.
3. Remove jumper wires and proceed with fuel system service.

Note. DO NOT energize injector longer than 10 seconds or damage may result to fuel injector.

Removal

1. Remove air cleaner and perform fuel system pressure release. Disconnect negative battery cable. Disconnect all vacuum hoses and electrical connectors.
2. Remove throttle cable. Remove speed control cable and transmission kickdown cable (if equipped). Remove return spring and fuel lines. Remove throttle body mounting screws and remove throttle body.

Note. Never use silicone lubricants on "O" rings or seals, as damage may result.

Installation

Using a new gasket, mount throttle body to intake manifold. Reverse removal procedure to complete installation.

1. Remove air cleaner and perform fuel system pressure release. Disconnect negative battery cable. Remove 3 screws attaching pressure regulator to throttle body. CAUTION: Place a shop towel around fuel inlet chamber to contain any fuel remaining in the system.
2. Pull pressure regulator from throttle body. Carefully remove "O" ring from pressure regulator and remove old gasket.

Install new gasket and "O" ring. Reverse removal procedure and check regulator for leaks to complete installation.

1. Remove air cleaner assembly and perform fuel system pressure release. Disconnect negative battery cable. Remove pressure regulator.
2. Remove screw holding down injector cap. Using 2 small screwdrivers lift cap off injector using slots provided. Place a small screwdriver in hole in front of electrical connector.
3. Gently pry injector from pod. Ensure that injector lower "O" ring have been removed from pod.

Install new "O" ring on injector. The new injector should already have a new "O" ring installed. Apply a light coating of caster oil or petroleum jelly on "O" rings. Reverse removal procedure to complete installation.

Note. Ensure that injector and cap are keyed in the proper position.

Disconnect negative battery cable and remove air cleaner. Disconnect 3-way connector at TPS. Remove 2 screws attaching TPS to throttle body. Pull TPS off throttle shaft.

Reverse removal procedure to install. Tighten screws to 20 INCH lbs. (2 N.m).

Remove air cleaner and disconnect and throttle cables from throttle body linkage. Remove 2 screws from throttle cable bracket and lay bracket aside. Disconnect wiring and unscrew sensor.

Apply heat transfer compound to tip portion of new sensor. Reverse removal procedure to complete installation.

Remove air cleaner and negative battery cable. Disconnect 4-pin connector. Remove temperature sensor from throttle housing. Remove 2 screws and remove AIS motor from throttle body housing. Ensure that "O" rings are removed with AIS motor.

Ensure that pintle is in retracted position. If pintle measures more than one inch (25 mm), it must be retracted using ATM test code 03. For further information on this test procedure see appropriate article in COMPUTERIZED ENGINE CONTROLS section. Battery should be connected for this procedure. Replace all "O" rings and reverse removal procedure to complete installation.

Removal & Installation

Remove air cleaner duct from SMEC and remove battery. Remove 2 mounting screws and wiring connectors from module. Remove module. To install reverse removal procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS