Engine Controls - Theory & Operation Dodge Shadow I

INTRODUCTION

This article covers the basic description and operation of engine performance related systems and components. Read this article before working on unfamiliar systems.

AIR INDUCTION SYSTEM

Chrysler-built Throttle Body Injection (TBI) engines use an aluminum long-branch fan designed intake manifold. Intake plenum is remote. The throttle body is installed on the upper plenum of intake manifold.

The 4-cylinder Port Fuel Injected (PFI) engines use an aluminum intake manifold with upper plenum and lower intake runners. These intake manifolds are also machined for fuel rail attachment and injector installation. The throttle body is installed on upper plenum of intake manifold.

The 3.0L engine uses a large aluminum plenum and cross type intake manifold. (Scheme 1) The throttle body is installed on upper plenum of intake manifold. The 3.3L engine uses a 2 piece aluminum intake with individual primary runners. The intake manifold provides a mounting surface for EGR valve and PCV valve.

Scheme 1

TURBOCHARGER I

The turbocharging system is mounted on the manifold side of engine. (Scheme 2) It includes a turbine assembly, center housing rotating assembly, compressor assembly, wastegate, and throttle body. The turbine is spun by exhaust gas causing compressor wheel to draw in air.

Maximum manifold pressure (boost) is controlled by the wastegate solenoid. Operation of the wastegate is controlled by varying duty cycle of wastegate solenoid. This is accomplished by the Single Board Engine Controller (SBEC).

Scheme 2

TURBOCHARGER IV

With engine idling or in a cruise condition, exhaust volume is low. Turbocharger vanes are held open to minimize exhaust restriction without producing boost.

When throttle is opened, vanes are briefly moved to restrict exhaust flow and increase exhaust velocity. This causes turbine wheel to accelerate rapidly. When engine speed and power increase, exhaust volume increases. Vanes are opened again to allow for maximum boost.

The Variable Nozzle Turbo (VNT) solenoids are controlled by the SBEC. The SBEC varies the duty cycle of each solenoid to accomplish vane positioning in turbocharger.

CONTROL UNIT

The Single Board Engine Controller (SBEC) is a digital computer that controls air/fuel ratio, canister purge, charging system, cooling fan, emission control devices, fuel injector pulse width, idle speed, ignition coil dwell, spark advance, turbocharger wastegate (Turbo I) and turbocharger vane position (Turbo IV).

The SBEC has a voltage converter that converts battery voltage to a regulated 5 volts and 8 volts output. The 5 volts is used to power Manifold Absolute Pressure (MAP) sensor, Throttle Position Sensor (TPS) and logic circuits on all engines except 3.3L V6. On 3.3L, 5 volts is used to power MAP and TPS only. The regulated 8 volts is used to power distributor on all engines except 3.3L. On 3.3L 8 volts is used to power cam and crankshaft sensors.

Note. For ease of understanding, components are grouped into 2 categories. The first category, INPUT DEVICES, are components which control or produce voltage signals that are monitored by the ECU. The second category, OUTPUT SIGNALS, are components that are controlled by the ECU (this is usually accomplished by the ECU grounding individual circuits).

INPUT DEVICES

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article. The available input signals include the following

BRAKE SWITCH

This input tells SBEC vehicle is in a stopped condition.

CAMSHAFT ANGLE SENSOR

The cam sensor is mounted on top of timing chain cover. This sensor reads slots in cam timing sprocket. The SBEC uses this information along with crankshaft sensor to determine if fuel injectors and ignition coils are properly adjusted for correct cylinders.

CHARGE TEMPERATURE SENSOR

This sensor is only used on Turbo IV engines and mounted in intake manifold. The sensor measures incoming intake air. This information is used by SBEC to adjust air/fuel mixture and turbocharger boost.

CLUTCH SWITCH

This input prevents engine from starting until clutch pedal is depressed.

COOLANT TEMPERATURE SENSOR

The CTS monitors engine coolant temperature. This sensor is mounted in thermostat housing. Coolant temperature information is used by SBEC to slightly richen or lean air/fuel mixture, adjust idle speed and control cooling fans as necessary according to engine temperature. On turbo engines, CTS is also used to control boost levels and spark advance.

CRANKSHAFT ANGLE SENSOR

The crankshaft sensor is mounted on transaxle bellhousing. The sensor reads slots (4 per cylinder) on torque converter drive plate. The SBEC uses this information to determine crankshaft position.

DENOTATION SENSOR

On 4-cylinder turbo models, the detonation sensor is mounted in the intake manifold in such a position so sensor can detect detonation in any cylinder. This sensor generates an input signal to SBEC when detonation occurs. The SBEC uses this input to adjust spark advance and boost schedules.

On 3.3L, detonation sensor is mounted on engine block where detonation in any cylinder can be detected. The SBEC uses this information to adjust spark advance.

HALL EFFECT SWITCH

Used on 4-cylinder engines only, Hall Effect pick-up is located inside distributor. This switch supplies SBEC with engine RPM data and ignition timing information. Sensor also supplies SBEC with fuel synchronization data (turbo only). SBEC uses this information to advance or retard ignition timing as necessary.

MANIFOLD ABSOLUTE PRESSURE SENSOR

The MAP sensor monitors manifold vacuum. This sensor transmits information on manifold vacuum and barometric pressure to the SBEC. MAP sensor information is used in conjunction with other sensors to adjust air/fuel mixture.

On turbocharged engines, MAP sensor is also used to adjust spark advance and turbocharger wastegate or vane position.

OPTICAL DISTRIBUTOR

Used on 3.0L only, the optical distributor provides engine speed and crankshaft position signals. The SBEC uses this information to control fuel injection, ignition timing and idle speed. (Scheme 3)

Scheme 3

OXYGEN SENSOR

The O2 sensor produces a small electrical voltage (.1-.9 volt) when exposed to oxygen in exhaust gas flow. O2 sensor is electrically heated for faster switching.

When a large amount of oxygen is present in exhaust gas, O2 sensor will produce a low voltage (.1 volt). With a small amount of oxygen present in exhaust gas, O2 sensor will produce a high voltage (.9 volt).

With the O2 sensor monitoring the oxygen content in exhaust gas, the sensor acts like a rich/lean switch. This information is used by SBEC to adjust air/fuel ratio.

P/N SWITCH

The Park/Neutral switch is located on transaxle housing. This switch prevents engine starter from engaging if vehicle is in any gear except Park or Neutral.

THROTTLE BODY TEMPERATURE SENSOR

This sensor is mounted in throttle body. The sensor monitors throttle body temperature so SBEC can adjust air/fuel mixture for a hot restart condition.

THROTTLE POSITION SENSOR

The TPS is mounted on throttle body and monitors opening angle of throttle valve. The SBEC uses this information along with other sensor inputs to adjust air/fuel ratio.

VEHICLE SPEED SENSOR

The VSS generates 8 pulses per axle shaft revolution. The SBEC will interpret speed sensor input along with throttle position sensor closed throttle input.

This will allow SBEC to differentiate between closed throttle decel and closed throttle idle (vehicle stopped) conditions. During decel, SBEC controls Automatic Idle Speed (AIS) motor to maintain a desired manifold pressure value. During idle (vehicle stopped), SBEC controls AIS motor to maintain a desired idle speed.

OUTPUT SIGNALS

Note. Each vehicle may be equipped with different combinations of computer controlled components. The following listed components may NOT be used on all models. For theory and operation on each output component, refer to the system indicated in brackets, to the right of each component.

1. A/C Cut-Out Relay (Miscellaneous)
2. Alternator (Miscellaneous)
3. Automatic Idle Speed (AIS) Motor (Idle Speed)
4. Auto Shutdown (ASD) Relay (Miscellaneous)
5. CHECK ENGINE Light (Self-Diagnostic System)
6. Electric Exhaust Gas Recirculation Transducer (EET) (Emission Systems)
7. Exhaust Gas Recirculation (EGR) Solenoid (Emission Systems)
8. Fuel Injector(s) (Fuel Injector)
9. Ignition Coil(s) (Ignition System)
10. In-Tank Fuel Pump (Fuel Delivery)
11. Lock-Up Torque Converter Solenoid (Transmission Control)
12. Purge Solenoid (Emission Systems)
13. Radiator Fan Relay (Miscellaneous)
14. Speed Control Servo (Miscellaneous)
15. Variable Nozzle Turbo (VNT) Solenoid (Air Induction System)
16. Wastegate Solenoid (Air Induction System)

AUTOMATIC SHUTDOWN (ASD) RELAY

The ASD relay is energized when ignition is on. If SBEC does not receive a distributor signal, SBEC will de-energize ASD relay. When ASD is de-energized, power to fuel pump, fuel injectors, ignition coil and O2 sensor heater element is interrupted.

FUEL PRESSURE DAMPER

The fuel pressure damper is only used on 3.3L. Damper is located downstream of fuel pressure regulator. (Scheme 4) It dampens fuel pressure pulsations which are caused when injectors are opened and closed. An internal rubber diaphragm with an air pocket on one side absorbs pressure pulses.

Scheme 4

FUEL PRESSURE REGULATOR (TBI)

The fuel pressure regulator is a mechanical device located on top of throttle body. Its purpose is to maintain a constant 14.5 psi (1.0 kg/cm 2 ) at fuel injector. Inside the pressure regulator is a spring loaded diaphragm.

When fuel pump is energized, fuel flows past fuel injector into fuel pressure regulator. The pressure regulator restricts fuel from flowing any further until 14.5 psi (1.0 kg/cm 2 ) is reached.

When proper fuel pressure is reached, fuel pressure pushes on a spring behind the diaphragm. As fuel pressure moves spring and diaphragm, a return line to fuel tank is uncovered. This allows excess fuel to return to fuel tank keeping fuel pressure constant across injector.

FUEL PRESSURE REGULATOR (PFI)

The fuel pressure regulator is a mechanical device located on fuel injector rail, downstream of fuel injectors. (Scheme 4) Its purpose is to maintain a constant fuel pressure across fuel injectors. See FUEL PRESSURE FUEL PRESSURE. Inside the pressure regulator is a spring loaded diaphragm.

When fuel pump is energized, fuel flows past fuel injector into fuel pressure regulator. The pressure regulator restricts fuel from flowing any further until correct fuel pressure is reached.

When proper fuel pressure is reached, fuel pressure pushes on a spring behind the diaphragm. As fuel pressure moves spring and diaphragm, a return line to fuel tank is uncovered. This allows excess fuel to return to fuel tank keeping fuel pressure constant across injectors.

FUEL PRESSURE

IN-TANK FUEL PUMP (TBI)

The fuel pump is an immersible electric pump with permanent magnet motor. The pump incorporates a sock attached to pump pick-up. Fuel pump also contains a check valve which restricts fuel movement in either direction when pump is not operational. Voltage to operate pump is supplied through ASD relay.

IN-TANK FUEL PUMP (PFI)

The fuel pump is a positive displacement, immersible gerotor pump with a permanent magnet motor. The pump incorporates a sock attached to pump pick-up.

This fuel pump contains 2 check valves. One check valve is used to relieve internal pump pressure and regulate maximum fuel pump output. The other check valve located near pump outlet, is used to restrict fuel movement in either direction when pump is not operational. Voltage to operate pump is supplied through ASD relay.

THROTTLE BODY INJECTION (TBI)

The fuel injector is an electronic solenoid. The SBEC determines when and for how long the injector should be energized. While electrical current is supplied to the injector, a spring loaded check ball is lifted from its seat. Fuel then flows in a cone shaped spray pattern before entering air stream.

PORT FUEL INJECTION (PFI)

The fuel injectors are electric solenoid powered and controlled by SBEC. The SBEC determines when and how long the injector should operate. When an 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.

AUTOMATIC IDLE SPEED (AIS) MOTOR

The AIS motor adjusts idle speed to compensate for engine load and ambient temperature. The AIS motor varies amount of air by-pass through throttle body.

The SBEC uses coolant temperature, distance (speed) sensor, throttle position and various switch input operations to adjust AIS to obtain optimum idle conditions. Deceleration stall is prevented by increasing airflow when throttle is closed suddenly.

DIRECT IGNITION SYSTEM (DIS)

The crankshaft position sensor senses slots (4 per cylinder, 20 degrees apart) around an extension of the drive plate. Basic timing is preset by crankshaft sensor position and is not adjustable. By using a crankshaft sensor, spark scatter has been eliminated.

A cam sensor is located on timing chain cover. Cam sensor senses slots on cam timing gear. Fuel injection synchronization and cylinder identification are provided through cam sensor. A unique combination of slots on cam gear are used to identify cylinders and initiate fuel and spark for start and run conditions.

The SBEC fires one coil at a time. This one coil in turn fires 2 spark plugs at once. One cylinder is on compression stroke and the other cylinder is on exhaust stroke. A low primary resistance allows SBEC to fully charge ignition coils for each firing. (Scheme 5)

Scheme 5

OPTICAL IGNITION SYSTEM (3.0L)

The timing member is a thin disk, mounted on distributor shaft and driven at 1/2 crankshaft speed. Disk has 2 sets of slots on its surface. (Scheme 3) The outer, high data rate set of slots occurs at intervals of 2 degrees of crankshaft rotation. It is used for ignition timing at engine speeds up to 1200 RPM to increase timing accuracy.

During cranking and idle, engine speed changes with firing pulse of each cylinder. The high data rate signal is used to trigger ignition at correct crankshaft position regardless of these speed changes.

The inner, low data rate set contains 6 slots, which are correlated to piston TDC for each cylinder. This set is used to trigger fuel injection system and operation at speeds greater than 1200 RPM where speed changes due to individual firing pulses are small. This set of slots is also used for ignition timing. Light Emitting Diodes (LED's) and photo diodes are mounted in facing positions on opposite sides of the disk, in-line with the slots.

Masks over LED's and photo diodes focus light beams onto photo diodes. As each slot passes between diodes, light beam is turned on and off. This creates an alternating voltage in each photo diode which is converted into on-off pulses by an integrated circuit within distributor. These pulses are transmitted to SBEC.

IGNITION TIMING CONTROL SYSTEM

The Single Board Engine Controller (SBEC) completely controls ignition system. During a crank/start mode, SBEC will set a fixed amount of spark advance for an efficient engine start.

IGNITION TIMING ADVANCE CONTROL

The amount of spark advance or retard is determined by inputs that SBEC receives from coolant temperature, engine vacuum and engine RPM. During engine operation the SBEC can supply an infinite number of advance curves to ensure proper engine operation.

AIR ASPIRATOR SYSTEM

Some throttle body fuel injected engines use an air aspirator system. (Scheme 6) This system incorporates a valve that uses exhaust pressure pulsation to draw fresh air from air cleaner into exhaust system.

This fresh air introduced into exhaust system helps reduce carbon monoxide (CO) and hydrocarbon (HC) emissions. The aspirator valve works most efficiently at idle and slightly off idle conditions. This is when exhaust pulsations are strongest. The aspirator valve remains closed with higher engine speeds.

Scheme 6

EVAPORATIVE EMISSION SYSTEM

This system stores fuel vapors from fuel tank, preventing vapors from reaching the atmosphere. As fuel evaporates inside fuel tank, vapors are routed inside vent hoses to charcoal canister, located in wheelwell area, where they are stored until engine is started.

Charcoal canister purging is controlled by a canister purge solenoid. The canister purge solenoid is controlled by SBEC. During engine warm-up and for a short period after hot restarts, SBEC grounds canister purge solenoid causing solenoid to energize.

When canister purge solenoid is energized, this prevents engine vacuum signal from reaching charcoal canister. After engine reaches a predetermined operating temperature and a timer has run out, SBEC will de-energize canister purge solenoid. This will allow engine vacuum to purge charcoal canister. Canister purge solenoid will also be de-energized during certain idle conditions so SBEC can update fuel delivery calibration.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

The EGR system allows a predetermined amount of exhaust gas to enter cylinder with the air/fuel mixture. This dilution of cylinder air/fuel volume reduces Oxides of Nitrogen (NOx) and reduces peak temperatures inside combustion chamber.

PORT FUEL INJECTED ENGINE EGR

This system is used on 2.5L Turbo I engines with California emissions only. The EGR system is a backpressure type. The backpressure transducer measures amount of exhaust gas backpressure on exhaust side of EGR valve. The backpressure transducer then varies the amount of vacuum applied to EGR valve.

This system allows backpressure transducer to provide proper vacuum signal to EGR valve for all engine operating conditions. EGR system is also controlled by an EGR vacuum solenoid. The EGR solenoid does not allow EGR at idle.

On 3.3L, EGR system uses an Electric Exhaust Gas Recirculation Transducer (EET). This system incorporates backpressure transducer and EGR solenoid into one unit. (Scheme 7)

Scheme 7

THROTTLE BODY INJECTED ENGINE EGR

The EGR system on these engines uses an EGR valve mounted on the intake manifold and a tube connecting exhaust manifold with intake manifold. EGR system operates at any temperature on these engines.

POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM

Crankcase and piston blow-by gases are removed from crankcase with manifold vacuum. These gases are introduced into incoming air/fuel mixture and become part of the calibrated mixture. No fresh air enters crankcase with this PCV system.

THERMOSTATIC AIR CLEANER (TAC)

Only Throttle Body Injection (TBI) engines use this system. This system controls incoming air temperature into throttle body when ambient temperatures are low. By using heated air, this allows the throttle body to be calibrated leaner, provide better cold driveability and helps prevent throttle body icing.

When ambient temperature is 15°F (9°C) or more above the control temperature, air flow will be through outside outlet. When ambient temperature is less than control temperature, airflows through both air inlets after engine has been started.

With a colder ambient temperature, more air flows past exhaust manifold to heat incoming air. With a warmer ambient temperature, more air flows through air cleaner snorkel by-passing exhaust manifold.

Control of incoming air temperature is controlled by intake manifold vacuum, temperature sensor (inside air cleaner assembly) and a vacuum diaphragm which operates door inside air cleaner snorkel.

Vacuum diaphragm is opposed by a spring. Temperature control occurs during road load conditions or when intake manifold vacuum is above the operating vacuum of vacuum diaphragm.

SELF-DIAGNOSTIC SYSTEM

The Single Board Engine Controller (SBEC) monitors several different circuits of engine control system. If a problem is sensed with a monitored circuit, SBEC will store a trouble code to aid technician in diagnosis of system. The CHECK ENGINE light or Diagnostic Readout Box-II (DRB-II) can be used to read trouble codes.

CHECK ENGINE LIGHT

The CHECK ENGINE light illuminates each time ignition switch is turned on. Light stays on for 3 seconds as a bulb test. If SBEC receives an incorrect signal or no signal from battery voltage input, charging system, Coolant Temperature Sensor (CTS), Manifold Absolute Pressure (MAP) Sensor, Throttle Position Sensor (TPS) or an emission related fault (California vehicles only) CHECK ENGINE light is illuminated. This warns driver that SBEC is in limp-in mode and immediate repairs are necessary. CHECK ENGINE light can also be used to display fault codes. For additional information, see SELF-DIAGNOSTICS article.

MISCELLANEOUS CONTROLS

Note. Although not strictly considered part of "Engine Performance" system, some controlled devices can adversely affect driveability if they malfunction.

A/C CLUTCH RELAY

A/C clutch relay is controlled by SBEC and A/C switch. A/C relay is powered by radiator fan relay. This relay is energized during engine operation when A/C switch is closed and blower switch is on.

When SBEC senses low idle speed or Wide Open Throttle (WOT) through Throttle Position Sensor (TPS), it will de-energize A/C relay preventing A/C operation.

ALTERNATOR

Chrysler Motors passenger cars use either a Nippondenso or a Bosch alternator. The 3.0L and 3.3L engine use Nippondenso alternators. The 2.2L and 2.5L engines may be equipped with either a Bosch or Nippondenso unit.

The alternator consists of a rotor, stator, rectifiers, front and rear covers and drive pulley. On all vehicles, voltage regulation is controlled by the Single Board Engine Controller (SBEC).

Alternator diodes convert AC current to DC current. The engine controller monitors critical input and output of the charging system, making sure it is working properly.

The engine controller will store in memory any failures within the monitored circuits. Engine controller will translate a failure in the form of fault codes when on-board diagnostics are entered.

The system's self-diagnostic abilities, if properly used, can simplify testing. The engine controller is programmed to monitor several different engine control system circuits. If a problem is sensed with a monitored circuit, a fault code is stored in the engine controller's memory. The check engine light will illuminate and engine controller may enter limp-in mode, if necessary. In this mode, engine controller attempts to compensate for the component or circuit by substituting information from other sources. This allows vehicle to operate until proper repairs are made.

ALL EXCEPT 3.3L

When distributor signal is not present with ignition switch in RUN position, ASD relay turns off power to electric fuel pump, fuel injectors, ignition coil and O2 sensor heating element.

3.3L

When there is no cam or crankshaft sensor signal with ignition switch in RUN position, ASD relay turns power off to electric fuel pump, fuel injectors, ignition coil and O2 sensor heating element.

EXCEPT DYNASTY, FIFTH AVENUE, IMPERIAL & NEW YORKER WITH V6

The Single Board Engine Controller (SBEC) controls radiator fan relay. The radiator fan relay will be energized during the following conditions

1. Fan relay is energized when A/C clutch is engaged.
2. On non-A/C cars and A/C cars with A/C not engaged, fan relay will energize at vehicle speeds more than 40 MPH and if coolant temperature reaches 230°F (110°C). Fan relay will turn off when coolant temperature reaches 220°F (104°C). When vehicle speed is less than 40 MPH, fan relay switches on at 210°F (99°C) and off at 200°F (93°C).
3. Fan relay also prevents "steaming". "Steaming" happens when moisture evaporates from outside of radiator when no ram air blows it under the car. Fan relay will energize when ambient temperature is less than 60°F (16°C), with coolant temperature between 100°F (38°C) to 195°F (91°C), engine at idle, zero vehicle speed and fan relay will energize for only 3 minutes.

DYNASTY, FIFTH AVENUE, IMPERIAL & NEW YORKER WITH V6

The Single Board Engine Controller (SBEC) controls radiator fan relay. The SBEC controls fan relay based on coolant temperature and A/C head pressure. Radiator fan relay will be energized during the following conditions

1. When coolant temperature reaches 210°F (99°C) and de-energize at 200°F (93°C) regardless of vehicle speed.
2. When A/C head pressure reaches 220 psi (15.5 kg/cm 2 ) and will de-energize when head pressure reaches 160 psi (11.2 kg/cm 2 ).

SPEED CONTROL SERVO

Multi-function control lever on steering column incorporates a slide switch which has 3 positions: OFF, ON and RESUME SPEED. The SET speed button is located at the end of a lever. Speed control servo is controlled by SBEC. This system will operate at speeds between 35-85 MPH.

See also:
• FUEL PRESSURE