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 dash behind right kick panel, under right side of dash, or under instrument panel.
The EEC-IV system controls three 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 air/fuel mixture control is accomplished by an airflow controlled, multi-point fuel injection system on all engines. The system provides self-diagnostic capabilities.
The EEC-IV ignition system is controlled by the ECA through a Thick Film Integrated (TFI-IV) ignition module. Ignition timing (advance or retard) and dwell are controlled with this system to improve ignition system performance. The ignition coil is an "E-Core" version and replaces the earlier oil filled coil.
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, switches, and actuators. In order for the ECA to perform properly, it must be kept constantly informed of engine operating conditions.
It is the task of the engine sensors to supply the ECA, via electrical signals, with specific information required to determine engine operating conditions. The ECA will then send out electrical signals to control air/fuel ratio, emission controls, idle speed and ignition timing. Individual component operation is as follows
A/C Compressor Clutch (ACC) Signal
Whenever battery voltage is applied to A/C 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. Idle speed is increased by using a throttle air by-pass valve.
Air Charge Temperature (ACT) Sensor
The ACT sensor is threaded into cylinder runner of intake manifold or attached to air cleaner. It 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).
Brake On/Off (BOO) Switch (All Except 4.9L & 5.0L)
The brake on/off switch signals the ECA whenever brakes are applied and/or released.
Detonation (Knock) Sensor (All Except 3.0L)
The knock sensor is a piezoelectric device designed to resonate at approximately the same frequency as engine knock. This unit senses and amplifies engine detonation (knock) and signals ECA to retard timing.
EEC Power Relay
This relay is activated by ignition switch. The relay supplies battery voltage to ECA when ignition switch is on.
EGR Valve Position Sensor (EVP) (All Except 3.0L)
This sensor is located on top of the EGR valve. It tells the ECA the position of the EGR valve.
Engine Coolant Temperature (ECT) Sensor
This sensor, threaded into heater outlet fitting or engine cooling passage, monitors engine coolant temperature. The ECA is sent a signal throughout the entire range of operating temperatures. In turn, the ECA modifies air/fuel mixture, ignition timing, and EGR operation.
Inferred Mileage Sensor (IMS) (5.0L Engine)
The IMS circuit uses an E-cell which deflates with each application of current. When E-cell is completely deflated, the calibration parameters in the ECA will change, thus compensating for vehicle aging.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor measures pressure in intake manifold and sends a signal to ECA that is proportional to absolute pressure. It is mounted in the right inner fender area. On F-Series pickups with air conditioning, it is mounted on evaporator case. On E-Series pickups, it is mounted on right section of cowl.
Neutral Drive Switch (NDS), Neutral Gear Switch (NGS) &
Clutch Engage Switch
The NDS switch is used in automatic transmission equipped vehicles to adjust idle speed due to the increased loading of an engaged transmission. Vehicles with manual transmissions use an NGS switch to notify the ECA when transmission is in or out of gear. A clutch engage switch is also used.
Heated Exhaust Gas Oxygen (HEGO) Sensor (All Except 5.0L Econoline)
This sensor 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.
Profile Ignition Pick-Up (PIP)
The PIP informs the ECA of crankshaft position and speed. PIP assembly is integral with distributor on all models. PIP has an armature with 4 windows and 4 metal tabs that rotate past a stator assembly (Hall effect switch). The ignition distributor does not have any mechanical or vacuum advance.
Power Steering Pressure Switch (PSPS) (All Except 2.9L)
The power steering pressure switch signals the ECA when power steering pressure exceeds 400-600 psi (28-42 kg/cm 2 ).
Pressure Feedback Electronic (PFE) EGR Valve & Transducer (2.9L)
The PFE exhaust gas recirculation valve is a conventional ported EGR valve with a backpressure sensing element attached to it. The valve is used in conjunction with the backpressure transducer to inform ECA of EGR valve position.
The PFE transducer converts varying exhaust pressure signals into a proportional analog voltage which is digitized by the ECA. The ECA uses the signals received from the transducer to complete optimum EGR flow.
Self-Test Input (STI)
Self-Test Input (STI) trigger is a wire (pigtail) near SELF-TEST connector. It is used to activate SELF-TEST. SELF-TEST procedures are built into EEC-IV control module so system can display service codes for diagnosis of intermittent problems.
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. The TPS creates an electrical signal and transmits it to ECA. These signals keep ECA informed of wide open throttle, closed throttle, or normal cruise conditions.
Canister Purge Solenoid (CANP) (3.0L)
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 by Eca.
Converter Clutch Override (CCO) Solenoid (2.3L & 3.0L)
Used on automatic transmission equipped models only, the CCO solenoid allows the ECA to control torque converter operation.
EGR Control (EGRC) Solenoid (2.3L)
Solenoid switches manifold vacuum to operate EGR valve on command from ECA. Vacuum opens the EGR valve when the solenoid is energized.
EGR Vent (EGRV) Solenoid (2.3L)
Solenoid vents EGR control solenoid vacuum line. When vent solenoid is energized, control solenoid can open EGR valve.
Fuel Injectors
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). The ECA controls length of time each injector is open. The "open" time of injector governs amount of fuel delivered.
Fuel Pump Relay
Fuel pump relay is activated by ECA with ignition in on or crank positions. When ignition switch is turned on, relay is activated to supply initial line pressure to system.
Self-Test Output (STO)
The STO is a circuit in the ECA which transmits service codes, in the form of timed pulses, to either a VOM or diagnostic tester hooked-up at SELF-TEST connector. These pulses are read as diagnostic codes.
Shift Indicator Light (SIL) (2.3L)
Shift indicator light indicates to driver when to shift gears for optimum fuel economy. ECA activates light according to information received on engine speed and manifold vacuum levels.
Thermactor Air By-Pass (TAB) Solenoid (4.9L & 5.0L)
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 (4.9L & 5.0L)
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.
Thick Film Integrated (TFI) Ignition Module
The TFI ignition module is located on side of distributor. The ECA receives engine timing information from the distributor through the TFI ignition module. The ECA uses this information to control ignition timing and advance. The ECA triggers TFI by using a Spark Output (SPOUT) signal.
Throttle Air By-Pass Valve
The throttle air by-pass valve is a solenoid-operated valve controlled by ECA. The valve allows air to by-pass around throttle plates to control cold engine fast idle, no touch start, dashpot, overtemperature idle boost and engine load idle correction.
Wide Open Throttle A/C (WAC) Cut-Off (2.3L, 2.9L & 3.0L)
The WAC circuit is energized by ECA when wide open throttle condition is detected. During wide open throttle, power to the A/C compressor clutch is interrupted. The A/C remains off for about 3 seconds after returning to part throttle.
Vehicle Speed Sensor (VSS) (2.9L)
The vehicle speed sensor enhances idle speed control, controls transmission lockup, and provides and input for lean cruise operation.