Engine Controls - Theory & Operation Plymouth Acclaim I

INTRODUCTION

This article covers the basic description and operation of engine performance related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

TURBOCHARGERS

Turbocharging system is mounted on manifold side of engine. (Scheme 1) System includes a turbine assembly, center housing rotating assembly, compressor assembly, wastegate, and throttle body. Turbine is spun by exhaust gas causing compressor wheel to compress incoming air charge into manifold.

Scheme 1

Wastegate Solenoid

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

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 and turbocharger wastegate.

The SBEC has a voltage converter that converts battery voltage to regulated 5-volt or 8-volt outputs. The regulated 5-volt output is used to power Manifold Absolute Pressure (MAP) sensor, Throttle Position Sensor (TPS) and logic circuits. The regulated 8-volt output is used to power distributor on all engines except models equipped with Direct Ignition System (DIS). On models with DIS, an 8-volt output is used to power camshaft and crankshaft sensors.

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals that are monitored by the SBEC. The second category covers OUTPUT SIGNALS, which are components controlled by the SBEC.

INPUT DEVICES

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

A/C Control Module (ACM)

When A/C function is selected, the ACM sends a request signal to the SBEC approximately .5 second before A/C clutch is energized. The SBEC increases engine idle speed to compensate for increased engine load. Approximately .5 second before ACM de-energizes A/C compressor clutch, the ACM stops sending request signal and SBEC reduces idle speed to compensate for decrease in engine load.

Brake Switch

The brake switch is mounted on brake pedal support bracket. Brake switch is used as an input to the SBEC during deceleration and full stop conditions. Together with other inputs, brake switch is used to maintain engine idle speed by controlling Automatic Idle Speed (AIS) motor position.

Camshaft Angle Sensor

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

Charge Temperature Sensor

This sensor is mounted on intake manifold. The sensor measures temperature of incoming intake air/fuel mixture. This information is used by SBEC to adjust air/fuel mixture and turbocharger boost on 2.2L turbo engines.

Coolant Temperature Sensor (CTS)

The CTS monitors engine coolant temperature. This sensor is mounted in thermostat housing. Coolant temperature information is used by SBEC to slightly enrich or make 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 angle 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.

Detonation 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 and 3.8L V6 models, detonation sensor is mounted on engine block where detonation in any cylinder can be detected by sensor. The SBEC uses this information to adjust spark advance.

Hall Effect Switch

Used only on 4-cylinder engines, Hall Effect switch 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 (MAP) Sensor

The MAP sensor monitors manifold vacuum (engine load). 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 control.

Optical Distributor

Used only on 3.0L V6 engines, the optical distributor provides engine speed and crankshaft position signals to the SBEC. The SBEC uses this information to control fuel injection, ignition timing and idle speed. (Scheme 2)

Scheme 2

Oxygen Sensor

The O2 sensor produces a small electrical voltage (.1-.9 volt) when exposed to oxygen in exhaust gas flow. The 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.

Park/Neutral Switch

The P/N switch is located on transaxle housing. The switch provides an input to the SBEC indicating what position automatic transmission is in. Input is used to determine idle speed (varying with gear selection), fuel injector pulse width and ignition timing.

Throttle Body Temperature Sensor

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

Throttle Position Sensor (TPS)

The TPS is mounted on throttle body and monitors opening angle of throttle valve. TPS input voltage to the SBEC varies from .5 volt at minimum throttle opening (idle) to 4.5 volts at Wide Open Throttle (WOT). The SBEC uses this information along with other sensor inputs to adjust air/fuel ratio.

Vehicle Speed Sensor (VSS)

The VSS is located in transaxle extension housing. The VSS generates 8 pulses per axle shaft revolution. The SBEC will interpret VSS input along with TPS closed throttle input.

These inputs allow SBEC to differentiate between closed throttle decel and closed throttle idle (vehicle stopped) conditions. During deceleration, 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. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

A/C Cut-Out Relay

See MISCELLANEOUS CONTROLS.

Automatic Idle Speed (AIS) Motor

See IDLE SPEED.

Auto Shutdown (ASD) Relay

See FUEL DELIVERY.

Barometric Read Solenoid

See FUEL DELIVERY.

CHECK ENGINE Light

See SELF-DIAGNOSTIC SYSTEM.

Electric Exhaust Gas Recirculation Transducer (EET)

See EMISSION SYSTEMS.

Exhaust Gas Recirculation (EGR) Solenoid

See EMISSION SYSTEMS.

Fuel Injector(s)

See FUEL INJECTOR.

Fuel Pump Relay

See FUEL SYSTEM.

Ignition Coil(s)

See IGNITION SYSTEMS.

In-Tank Fuel Pump

See FUEL DELIVERY.

Lock-Up Torque Converter Solenoid

See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.

Purge Solenoid

See EMISSION SYSTEMS.

Radiator Fan Relay

See MISCELLANEOUS CONTROLS.

Speed Control Servo

See MISCELLANEOUS CONTROLS.

See AIR INDUCTION SYSTEM.

Automatic Shutdown (ASD) Relay

The ASD relay is energized when ignition is on. If SBEC does not receive a distributor signal (camshaft or crankshaft sensor signal on DIS models), SBEC will de-energize ASD relay. On Monaco and Premier, when ASD relay is de-energized, power to fuel injectors, ignition coil and alternator field is interrupted. On all other models, when ASD relay is de-energized, power to fuel pump, fuel injectors, ignition coil and O2 sensor heater element is interrupted.

A barometric read solenoid is used on turbo models to control switching of manifold pressure or atmospheric pressure supplied to MAP sensor. Atmospheric pressure is periodically supplied to MAP sensor to measure barometric pressure. Barometric information is used for fuel injection pulse width control. The barometric read solenoid is energized by the SBEC and is located in the MAP sensor vacuum line next to the MAP sensor.

Fuel Pump Relay (Monaco & Premier)

The fuel pump relay is located in the power distribution center mounted on left strut tower. Relay is controlled by the SBEC and is activated when ignition switch is in START or RUN positions. The relay supplies battery voltage to fuel pump and 02 heater element.

Fuel Pressure Damper

The fuel pressure damper is used only on 3.3L and 3.8L V6 models. Damper is located downstream of fuel pressure regulator. (Scheme 3) 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 3

Fuel Pressure Regulator

The fuel pressure regulator is a mechanical device located on top of throttle body on Throttle Body Injection (TBI) models or on fuel rail on Port Fuel Injection (PFI) models. The regulator is controlled by manifold vacuum. Its purpose is to maintain correct fuel pressure at fuel injector. A spring-loaded, vacuum assisted diaphragm is located inside pressure regulator.

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

During acceleration, vacuum to diaphragm drops off. Without vacuum assist, spring pressure only acts upon diaphragm, resulting in a slight increase in fuel pressure before return port is opened.

Fuel Pump

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.

FUEL INJECTOR

Fuel injector is an electronic solenoid. The SBEC determines pulse width (on time) for injector. When injector is energized, a spring-loaded check ball is lifted from its seat. Fuel then flows in a cone-shaped spray pattern into air stream on TBI models.

On PFI models, 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 directly behind intake valve.

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, VSS, TPS and various switch input operations to adjust AIS to obtain optimum idle conditions. Deceleration stall is prevented by increasing airflow when throttle is suddenly closed.

DIRECT IGNITION SYSTEM (DIS)

The crankshaft angle sensor detects 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 camshaft angle sensor supplies fuel injection synchronization and cylinder identification information by sensing slots located on camshaft sprocket or camshaft (Monaco and Premier). For sensor location, see the CAMSHAFT ANGLE SENSOR table.

The SBEC fires one coil at a time. This one coil in turn fires 2 spark plugs simultaneously. 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 4)

CAMSHAFT ANGLE SENSOR

Scheme 4

2.2L, 2.5L & 2.5L Turbo

A Hall Effect switch is located in distributor assembly. The pick-up supplies RPM, fuel injection synchronization (2.5L Turbo) and ignition timing data to the SBEC. The SBEC determines ignition spark timing and injector pulse width to maintain optimum driveability.

3.0L Engine

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 4) 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 Top-Dead Center (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) and photo diodes are mounted in facing positions on opposite sides of the disk, in-line with the slots.

Masks over LED 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.

Single Board Engine Controller (SBEC)

SBEC controls the 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 sensors. 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 5) This system incorporates a valve that uses exhaust pressure pulsation to draw fresh air through air cleaner assembly 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 when exhaust pulsations are strongest. Aspirator valve is closed at higher engine speeds.

Scheme 5

EVAPORATIVE EMISSION (EVAP) SYSTEM

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

Charcoal canister purging is controlled by SBEC through a canister purge solenoid. During engine warm-up and for a short period after hot restarts, SBEC energizes canister purge solenoid preventing vacuum signal from reaching charcoal canister.

After engine reaches a predetermined operating temperature and a timer has run out, SBEC de-energizes canister purge solenoid allowing engine vacuum to purge charcoal canister. Canister purge solenoid is also de-energized during certain idle conditions so SBEC can update fuel delivery calibration.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

Note. 2.2L Turbo is not equipped with EGR system. The 2.5L, 3.3L and 3.8L models equipped with EGR systems are California vehicles only.

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 peak temperatures inside combustion chamber which reduces Oxides of Nitrogen (NOx), and helps prevent spark knock.

The EGR system uses an Electric Exhaust Gas Recirculation Transducer (EET). (Scheme 6) The EET is a backpressure transducer and electric vacuum solenoid combined into a single unit.

The vacuum solenoid portion of the EET is controlled by the SBEC and is used to regulate vacuum to the transducer portion of EET. The backpressure transducer measures the 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.

Scheme 6

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.

THERMOSTATIC AIR CLEANER (TAC)

Used only on Throttle Body Injection (TBI) engines, this system controls incoming air temperature to 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, airflow will be through outside outlet. When ambient temperature is less than control temperature, air flows 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.

Temperature of incoming air charge 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 which closes air door when vacuum signal is removed. 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.

The CHECK ENGINE light illuminates each time ignition switch is turned on. Light stays on for 3 seconds as a bulb test. CHECK ENGINE light is illuminated if SBEC receives an incorrect signal or no signal from any of the following: 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). 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 G - TESTS W/ CODES in the ENGINE PERFORMANCE Section.

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

A/C CLUTCH RELAY

A/C clutch relay is controlled by SBEC and A/C switch. A/C clutch 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 clutch relay preventing A/C operation.

All Models (Except Dynasty, Fifth Avenue, Imperial & New Yorker With V6 Engines)

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

1. When A/C clutch is engaged.
2. At vehicle speeds more than 40 MPH and if coolant temperature reaches 230°F (110°C). Fan relay will de-energize 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, a condition where moisture evaporating from radiator core rises, giving the appearance of engine overheating. Fan relay will energize for about 3 minutes when ambient temperature is less than 60°F (16°C), with coolant temperature between 100°F (38°C) to 195°F (91°C), and when engine is at idle.

Dynasty, Fifth Avenue, Imperial & New Yorker With V6 Engines

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). Fan relay will de-energize at 200°F (93°C) regardless of vehicle speed.
2. When A/C system is engaged.
3. 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 ).

This system is electrically actuated and vacuum operated. The controls located on steering wheel consist of: OFF/ON, RESUME/ACCEL and SET/DECEL buttons. Speed control servo is controlled by SBEC. This system will operate at speeds above 35 MPH.

TRANSMISSION CONTROL

The SBEC controls lock-up of the torque converter through the part-throttle unlock solenoid. Torque converter is locked-up only when in direct drive mode.

See also:
• CAMSHAFT ANGLE SENSOR