DESCRIPTION
The center of the EEC-IV system is the Electronic Control Assembly (ECA). The ECA receives information from various sensors and switches. Based on information received and the operation program in the ECA's memory, the ECA generates output signals to control engine operation. The calibration module for EEC-IV system is mounted inside the ECA. The ECA is located in the passenger compartment, in one of the following locations: under the center console, under dash on left side of steering column, under passenger seat, or under dash behind right kick panel.
The 2.3L and 5.0L EFI models use the Bosch/Ford Electronic Fuel Injection system (EFI). The EFI system is classified as a multi point, pulse time, speed density, fuel injection system. The EEC-IV computer accepts inputs from various engine sensors to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range. The computer then outputs a command to the fuel injectors to meter the appropriate quantity of fuel.
The EEC-IV system controls 3 major areas of engine operation: Air/fuel mixture, ignition, and emission control. Additionally the system can control A/C compressor clutch operation and idle speed. The system provides self-diagnostic capabilities.
On all other models, the air/fuel mixture control is accomplished by use of a feedback carburetor (FBC). The ignition system is controlled by the ECA through a Thick Film Ignition (TFI-IV) module. Ignition timing (advance or retard) and dwell are controlled with this system to improve ignition system performance.
Emission control components controlled by this system include EGR and canister purge. These systems are normally off, but are turned on when the engine is ready to operate with the mixture change caused by EGR and canister purge operation.
The engine control system consists of the ECA, sensors and switches, and actuators. In order for the ECA to properly perform its function, it must be kept constantly informed of engine operating conditions.
It is the task of the engine sensors to supply the ECA, via electrical signal, with specific information required to determine engine operating conditions. The ECA can then send out electrical signals of its own to control air/fuel ratio, emission controls, idle speed, and ignition timing. Individual component operation is as follows
Airflow Meter Assembly (2.3L & 5.0L EFI Models)
The airflow meter consists of 2 sensors in a single housing, mounted between the air cleaner and throttle body assembly. An air flow sensor and an air temperature sensor are both exposed to intake airflow. The combined information from these sensors allows ECA to determine the mass and temperature of air entering engine.
Air By-Pass Solenoid
The Air By-pass Solenoid (ABS) is used to control engine idle speed and is operated by the EEC-IV module. The ABS allows air to pass around the throttle plates to control
- Cold engine fast idle.
- No touch start.
- Dashpot operation.
- Over temperature idle boost.
- Engine idle load correction.
Air Charge Temperature (ACT) Sensor (2.8L FBC Models Only)
The ACT is threaded into cylinder runner of intake manifold or attached to air cleaner. ACT provides ECA with air/fuel mixture temperature information. The ECA uses this information for correcting fuel flow and to control fuel flow during cold enrichment (cold starts).
A/C Compressor Clutch Signal (ACC) (5.0L & 5.8L FBC Models)
When battery voltage is applied to compressor clutch, a signal is sent to ECA. ECA uses signal to increase engine idle speed to compensate for added load created by A/C compressor.
EGR Valve Position Sensor (All Except 4.9L FBC Models)
This sensor is located on top of the EGR valve. It informs the ECA of EGR valve position.
Engine Coolant Temperature (ECT) Sensor
This sensor, threaded into heater supply tube, monitors engine coolant temperature. The ECA interprets this as either cold or normal operating temperature. This influences ECA control of fuel mixture enrichment, ignition timing, and EGR operation.
Fuel Injectors (2.3L & 5.0L EFI Models)
On EFI equipped engines, each cylinder has a solenoid operated injector which sprays fuel toward back of each inlet valve. Each injector is energized through ignition circuit and grounded through ECA to complete circuit. Injectors deliver 1/2 the amount of fuel required for an operating cycle each time they open (twice per cycle).
Idle Tracking Switch (ITS) (2.8L & 4.9L FBC Models Only)
The ITS is a mechanically operated electric switch held open by throttle linkage when throttle is closed. When throttle stop lever is against switch, ITS is open. The ITS is integral with the idle speed control motor.
Key Power
This is simply the test input for Quick Test using Key On Engine Off Self-Test. These tests are to detect hard faults only, not intermittent problems.
Knock Sensor (2.8L FBC Models Only)
This is a piezoelectric device designed to vibrate at about the same frequency as engine vibration. The sensor informs the ECA of engine knock and the ECA retards ignition timing until knock stops. The ECA will then go back to previous advance schedule, until knock is detected or engine operating conditions change.
Manifold Absolute Pressure (MAP) Sensor
Mounted on left or right inner fender, sensor measures absolute pressure of mixture in intake manifold and sends a signal to ECA that is proportional to absolute pressure in manifold.
Oxygen Sensor
This sensor is threaded into exhaust manifold where it constantly monitors oxygen content of exhaust gases. A voltage signal is produced which varies according to difference in oxygen content between exhaust gases and surrounding atmosphere. This signal is sent to the ECA which translates exhaust gas oxygen content to air/fuel ratio. It then alters air/fuel ratio to hold the ideal ratio for current engine operating conditions.
Park/Neutral Switch
Automatic transmission 2.8L models use a park/neutral switch. Switch indicates whether engine is loaded or unloaded and ensures that vehicle cannot be started in gear. ECA uses signal generated by switch to maintain same idle speed regardless of engine load.
Profile Ignition Pick-Up (PIP)
The PIP informs the ECA of crankshaft position and speed. PIP assembly is integral with distributor. PIP has an armature with 4 windows and 4 metal tabs that rotate past a stator assembly (Hall Effect Switch). Ignition distributor does not have any mechanical or vacuum advance. Distributor is adjustable for resetting base timing, if necessary.
Self-Test Input
Self-test input is a wire (pigtail) in Self-Test connector used to start the Quick Test. Self-Test procedures are built into EEC IV control module so system can display continuous Self-Test codes for diagnosis of intermittent problems.
Throttle Air By-Pass Valve (TABV) (2.3L & 5.0L EFI Models)
The TABV is a solenoid-operated valve controlled by ECA. The TABV operates a variable-area metering valve. Responding to commands from ECA, valve controls both cold and warm idle air flow. Valve causes air to by-pass throttle plate, thereby adjusting idle speed.
Throttle Position Sensor (TPS)
The TPS is mounted on side of throttle body and connected directly to throttle shaft. The TPS senses throttle movement and position and transmits an electrical signal to the ECA. These signals keep the ECA informed of wide open throttle, closed throttle, or normal cruise conditions.
EEC Power Relay
This relay is activated by ignition switch. Relay supplies battery voltage to ECA when switch is on. Some power relays incorporate a time delay of 5-10 seconds. If time delay is used, a throttle control activator assembly is also used.
Canister Purge Solenoid
This solenoid switches manifold vacuum to operate canister purge valve when a signal is received from ECA. Vacuum opens purge valve when solenoid is energized.
EGR Control Solenoid
Solenoid switches manifold vacuum to operate EGR valve on command from ECA. Vacuum opens EGR valve when solenoid is energized.
EGR Shut-Off Solenoid
EGR shut-off solenoid is an electrically-operated vacuum valve located between manifold vacuum source and EGR valve. A controlled vacuum bleed is located between solenoid and EGR valve. This vacuum bleed is a Backpressure Variable Transducer. These 2 devices operate EGR for optimum performance. Vacuum switched by solenoid is also supplied to canister purge solenoid valve.
EGR Vent Solenoid
Solenoid vents EGR control solenoid vacuum line. When vent solenoid is energized, control solenoid can open EGR valve.
Feedback Control Solenoid (FCS)
Feedback control is accomplished by this solenoid which regulates idle, off idle and main system air/fuel ratios according to ECA signals. The solenoid is mounted on the carburetor.
Idle Speed Control (ISC) Motor
This DC motor is used to provide idle speed control according to signals from ECA.
Self-Test Output
Part of the Self-Test connector, service codes are transmitted through the output in the form of timed pulses. These pulses are read as diagnostic codes.
Shift Indicator Lamp (2.8L & 4.9L FBC Models Only)
This lamp indicates to driver when to shift gears for optimum fuel economy. ECA signals lamp to light according to information received on engine speed and manifold vacuum levels.
TFI Ignition Module
The TFI module triggers ignition coil and determines dwell. Module is mounted on side of distributor. ECA uses signal from Profile Ignition Pick-Up to determine crankshaft position. Ignition timing is determined within ECA. ECA then signals TFI module when to fire coil.
Thermactor Air By-Pass (TAB) Solenoid
Solenoid provides a vacuum signal to by-pass valve in response to ECA signals. The TAB valve then by-passes thermactor pump air to atmosphere.
Thermactor Air Diverter (TAD) Solenoid
Solenoid provides a vacuum signal to diverter valve in response to ECA signals. The TAD valve then diverts thermactor pump air to either exhaust manifold or catalytic converter.
Throttle Kicker Solenoid
This is a 2-port valve with an atmospheric vent. A vacuum diaphragm is used to maintain nominal idle speed on command from ECA.
Variable Voltage Choke (VVC) (2.8L Models Only)
The ECA controls the choke rate by controlling voltage "on time" supplied to the choke. The voltage supplied to the choke is switched by the choke relay.
Temperature Compensated Accelerator Pump (TCP) (2.8L Only)
The ECA controls the TCP solenoid, which provides a vacuum signal to the carburetor. This vacuum signal is used to increase the accelerator pump shot when the engine is cold.