INTRODUCTION
This article covers 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.
TURBOCHARGER (CAPRI)
Capri turbo vehicles are equipped with a turbocharger mounted on the lower left front of the engine. Associated with it are an integral wastegate, and an intercooler mounted next to the radiator. A gauge on the instrument panel displays boost, and a buzzer warns of overboost.
Engine exhaust gas drives a turbine, which is on a common shaft with a compressor. Intake air from the air cleaner is compressed, then flows through an intercooler to the intake manifold. Compressor bearings are lubricated by engine oil, supplied through a tube from the engine.
COMPUTERIZED ENGINE CONTROLS
An Electronic Control Assembly (ECA) receives and processes signals from various sensors and switches. (Scheme 1) It then generates signals which control ignition timing, fuel injection functions, and various emission control devices. The ECA has system diagnostic capabilities, and will store trouble codes for use by service technicians.
Scheme 1
ELECTRONIC CONTROL ASSEMBLY (ECA)
The ECA is located under the instrument panel on the driver side. It receives and processes data from sensors, switches, and other components. The ECA generates output signals to control fuel injection, spark timing, other engine functions, and emission systems.
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category is OUTPUT SIGNALS, which are components controlled by the control unit.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input device usage for a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. The available input devices include the following
Barometric Pressure (BP) Sensor
This device senses changes in barometric pressure. The ECA uses this information in calculating fuel metering, ignition timing, and idle speed. On Festiva, the BP is incorporated into the ECA. On Capri, the BP is located on the passenger-side cowl.
Brake On-Off (BOO) Switch
This switch, located at the brake pedal, senses brake operation. The ECA uses this information in calculating fuel metering.
Clutch Engage Switch (CES)
This switch is located on the manual transaxle. It informs the ECA of transmission operating conditions. The ECA uses this signal for idle speed control and canister purge valve operation.
Crankshaft Position Sensor (CPS) (Festiva)
This sensor is located in the distributor. It sends engine RPM and crankshaft position data to the ECA. The ECA uses this signal in calculating fuel metering, ignition timing, idle speed control, and canister purge valve operation.
Cylinder Identification Sensor (CID) (Capri)
This sensor is located in the distributor. It provides crankshaft position data to the ECA for calculating fuel metering and ignition timing.
Electrical Load Switches
Blower control, cooling fan, rear window defroster, air conditioning, and headlight switches all send signals to the ECA. The ECA uses these signals for idle speed control.
Engine Coolant Temperature (ECT) Sensor
This sensor is located in the intake manifold. It sends coolant temperature data to the ECA. The ECA uses this signal in calculating fuel metering, idle speed control, and canister purge valve operation.
Exhaust Gas Oxygen (EGO) Sensor
This sensor is located in the exhaust manifold. It senses oxygen concentration in the exhaust gas. The ECA uses this signal in calculating fuel metering, idle speed control, and canister purge valve operation.
Neutral Safety Switch (A/T)
This switch is located on the automatic transaxle. It sends a signal to the ECA whenever the transaxle is in Neutral or Park ranges. The ECA uses this signal in calculating fuel metering, idle speed control, and canister purge valve operation.
Power Steering Pressure Switch (PSPS)
This switch is located on the power steering pump. It sends data about power steering operation to the ECA. The ECA uses this signal for idle speed control.
Throttle Position Sensor/Switch
The throttle position sensor/switch is located on the throttle body. On Capri, the ECA uses signals from Throttle Position Sensor (TPS). On Festiva, the ECA uses signals from Throttle Position (TP) switch for calculating fuel mixture, idle speed, A/C cut-off, and canister purge operation.
On Capri, the TPS sends a throttle plate angle signal to the ECA. A switch within the assembly sends a signal to the ECA when the throttle plate is in idle position.
On Festiva, the TP contains 2 switches. The Wide Open Throttle (WOT) Switch sends a signal to the ECA when the throttle valve is wide open. The Idle (IDL) Switch sends a signal to the ECA when throttle valve is at idle position.
Vane Airflow (VAF) Meter
This sensor is located in the air cleaner housing. It sends intake airflow data to the ECA. The ECA uses this signal in calculating fuel metering.
Vane Air Temperature (VAT) Sensor
This sensor is located inside the vane airflow sensor. It senses intake air temperature. The ECA uses this signal in calculating fuel metering, idle speed control, and canister purge valve operation.
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 of each output component, refer to indicated system.
Canister Purge Control Solenoid (EVAP-CPCS)
See EMISSION SYSTEMS.
CHECK ENGINE Light
See SELF-DIAGNOSTIC SYSTEM.
Fuel Injectors
See FUEL CONTROL.
Idle Speed Control By-Pass Air (ISC-BPA) Valve
See IDLE SPEED.
FUEL DELIVERY
Major components of the fuel delivery system are an electric fuel pump, fuel supply and return lines, a pressure regulator, fuel rail, and fuel injectors. (Scheme 2)or (Scheme 3).
Scheme 2
Scheme 3
Fuel Pump
The fuel pump, located inside the fuel tank, includes a check valve at the outlet and a filter element at the inlet. A pressure relief valve limits maximum fuel outlet pressure.
Fuel Pump Relay
This relay prevents fuel pump operation unless the engine is cranking or when a signal from the Vane Airflow (VAF) Meter confirms the engine is running. (Scheme 4) Internal circuitry holds the relay contacts closed during momentary loss of the VAF meter signal during rapid deceleration. The fuel pump relay is located under the center of the instrument panel, between the panel and the floor.
Scheme 4
Fuel Pressure Regulator
The fuel pressure regulator is located at the fuel return end of the fuel rail. It maintains fuel pressure within the fuel rail at a constant 36.3 psi (2.54 kg/cm 2 ) higher than intake manifold pressure.
Fuel Pressure Regulator Control Solenoid (PRC) (Capri)
This device closes the vacuum supply to the fuel pressure regulator on hot starts, thus increasing fuel pressure within the fuel rail and preventing fuel percolation which could cause hard starts during hot conditions. The PRC is located on the cowl panel, next to the canister purge solenoid.
Fuel Pump Inertia Switch
The fuel pump inertia (shut-off) switch is connected in series with the fuel pump. It opens to prevent fuel pump operation in the event of major collision or vehicle rollover. A reset button is provided to reset switch after it has been triggered. (Scheme 5)
Scheme 5
Electronic Fuel Injection (EFI)
The ECA receives a signal from the crankshaft position sensor (CPS) on Festiva, or from the cylinder identification (CID) sensor on Capri, for basic fuel injector timing. Signals to the ECA from other sensors and switches affect injector-on time. The amount of fuel injected is determined by duration of the electronic pulse sent to the fuel injector from the ECA.
Between idle and 5000 RPM, fuel is supplied by providing one injection per crankshaft rotation (2 injections per cycle) to all cylinders. There is one injection per 2 crankshaft rotations when engine speed exceeds 5000 RPM. When engine speed exceeds 6400 RPM, fuel injectors are shut off to prevent engine damage.
IDLE SPEED
While the engine is cold, the Idle Speed Control By-Pass Air (ISC-BPA) valve increases idle speed to warm the engine quickly. At engine temperatures less than 140°F (60°C), the valve is open. As the engine warms, the valve begins to close. The valve is fully closed at engine temperatures greater than 140°F (60°C). Idle speed is also affected by various switches, sensors, and load on the engine.
Capri
A pick-up coil within the distributor sends a signal to a Distributor-Mounted Ignition Module With Vacuum Advance (DMIVA) within the distributor. The DMIVA then sends a signal which fires the coil. When the coil fires, the distributor directs high voltage current to the spark plugs. The DMIVA system operates independently of the ECA.
Festiva
A pick-up coil within the distributor sends a signal to a transistorized ignition module on the coil bracket. A timing signal also goes from the ECA to the ignition module. The ignition module then sends a signal which fires the coil. When the coil fires, the distributor directs current to the spark plugs.
Spark timing is controlled by vacuum and centrifugal advance mechanisms and by a signal from the ECA. The ECA does not affect ignition timing on turbo models. On turbo models, a knock sensor and control unit retard ignition timing when knock occurs.
The ECA generates a spark timing signal from data received from the barometric pressure sensor, crankshaft position sensor, and vane airflow meter. This signal goes to the ignition module. The ignition module then sends a signal to fire the coil.
High Altitude Spark Advance Correction
A barometric pressure sensor is incorporated into the ECA on Festiva, and is a separate component on Capri. At high altitudes, the ECA sends a signal to the ignition module to advance ignition timing. This feature is not used on turbo models.
Knock Sensor (Capri Turbo)
A Knock Sensor (KS) generates a signal when knock occurs. A control unit processes this signal and then sends it to the ignition module to retard spark timing. The KS is located in the engine block, near the oil pressure switch.
Knock Control Unit (Capri Turbo)
The knock control unit filters normal engine vibration signals from the KS, then sends a signal to the ignition module to retard spark timing. This unit is located on right side of engine compartment.
DECELERATION SYSTEM (DASHPOT)
The deceleration control system closes the throttle plate gradually during deceleration. The dashpot prevents engine stalling on deceleration, and provides a smooth transition from deceleration to sudden acceleration.
Carbon Canister
The carbon canister stores vapors from the fuel tank until they are purged and burned in the engine. On Festiva, the carbon canister is located under the brake booster. On Capri, the carbon canister is located on the right side of the engine compartment near the cowl panel.
Canister Purge Control Solenoid
This component is connected between the carbon canister and intake manifold. When the ECA sends a signal to the solenoid to open, fuel vapors in the carbon canister are drawn into the engine. This solenoid is part of the canister purge control valve.
Canister Purge Control Valve
This valve opens to purge vapors from the carbon canister into the engine intake system.
Rollover Vent Valve
This valve, located in front of the fuel tank, blocks the vapor line in the event of vehicle rollover.
CATALYTIC CONVERTER
The catalytic converter is in the exhaust system, between the exhaust manifold and the muffler. It converts certain exhaust gases and pollutants into harmless substances.
PCV VALVE
The Positive Crankcase Ventilation (PCV) valve, located in the valve cover, controls the flow of blow-by gas from the crankcase to the intake manifold.
SELF-DIAGNOSTIC SYSTEM
Note. For additional information and operating procedures for the self-diagnostic system, refer to TESTS W/CODES article in the ENGINE PERFORMANCE Section.
The ECA monitors its inputs and outputs. When it detects a malfunction, it sets a code in the ECA and sends a signal to the CHECK ENGINE warning light. The light remains on until the malfunction is repaired. Trouble codes may be accessed at the Self-Test Output (STO) and Self-Test Input (STI) connectors, located near the battery.
If a sensor fails, the ECA will use a substitute value in its calculations to permit continued engine operation. In this condition, the vehicle will run, but driveability may be poor. Intermittent failures may result in the CHECK ENGINE warning light flickering or going out after the fault goes away. The corresponding trouble code, however, will be stored in the ECA. If fault does not recur, the related code will be erased from ECA memory.
Hard failures cause the CHECK ENGINE warning light to come on and remain on until the malfunction is repaired. If the warning light comes on and stays on during vehicle operation, determine and correct the cause of the malfunction.