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Electronic control system - description and precautions
Emissions control systems / Electronic control system - description and precautions


Description
The EEC-IV (FordТs fourth-generation Electronic Engine Control system) engine management system controls fuel injection by means of a microcomputer known as the ECU (Electronic Control Unit) (see illustrations).

2.1A Engine management system, showing fuel injection, ignition and emissions
2.1A Engine management system, showing fuel injection, ignition and emissions control sub-systems

1 ECU (Electronic Control Unit) 2 Fuel pump/fuel gauge sender unit 3 Fuel pump relay
4 Fuel filter
5 Idle speed control valve 6 Air mass meter
7 Air cleaner assembly
8 Fuel pressure regulator 9 Fuel rail
10 Throttle potentiometer 11 Intake air temperature sensor 12 Fuel injector
13 Camshaft position sensor 14 Charcoal canister
15 Charcoal canister-purge solenoid valve 16 Ignition coil
17 Battery
18 Ignition module - only separate (from ECU) on vehicles with automatic transmission
19 Coolant temperature sensor 20 Oxygen sensor
21 Crankshaft speed/position sensor 22 Power supply relay
23 Power steering pressure switch 24 Air conditioning compressor clutch solenoid 25 Service connector - for octane adjustment 26 Self-test connector - for Ford STAR tester diagnostic equipment 27 Diagnosis connector - for Ford diagnostic equipment FDS 2000 28 Ignition switch
29 Fuel cut-off switch
30 Exhaust Gas Recirculation (EGR) solenoid valve 31 Exhaust Gas Recirculation (EGR) valve 32 Exhaust Gas Recirculation (EGR) exhaust gas pressure differential sensor 33 Exhaust Gas Recirculation (EGR) pressure differential measuring point 34 To inlet manifold
35 Pulse-air filter housing 36 Pulse-air solenoid valve 37 Air conditioning/radiator electric cooling fan control 38 Automatic transmission control system - where applicable

2.1B Location of principal fuel injection, ignition and emissions control
2.1B Location of principal fuel injection, ignition and emissions control system components

1 ECU (Electronic Control Unit) 2 Self-test, diagnosis and service connectors (left to right) 3 Bulkhead component mounting bracket - manual transmission - showing from left to right, (EGR) solenoid valve, pulse-air solenoid valve and (EGR) exhaust gas pressure differential sensor 4 Bulkhead component mounting bracket - automatic transmission - showing from left to right, (EGR) solenoid valve, pulse-air solenoid valve and (EGR) exhaust gas pressure differential sensor, with separate ignition module above 5 Throttle housing, including potentiometer 6 Idle speed control valve 7 Intake air temperature sensor 8 Air mass meter
9 Exhaust Gas Recirculation (EGR) valve 10 Coolant temperature sensor 11 Crankshaft speed/position sensor 12 Pulse-air filter housing 13 Oxygen sensor
14 Ignition coil and spark plug (HT) leads 15 Camshaft position sensor 16 Fuel injector(s)
17 Power steering pressure switch 18 Air cleaner assembly
19 Air intake tube and resonators - under left-hand front wing 20 Resonator

The ECU receives signals from various sensors, which monitor changing engine operating conditions such as intake air mass (ie, intake air volume and temperature), coolant temperature, engine speed, acceleration/deceleration, exhaust oxygen content, etc. These signals are used by the ECU to determine the correct injection duration.

The system is analogous to the central nervous system in the human body - the sensors (nerve endings) constantly relay signals to the ECU (brain), which processes the data and, if necessary, sends out a command to change the operating parameters of the engine (body) by means of the actuators (muscles).

HereТs a specific example of how one portion of this system operates. An oxygen sensor, located in the exhaust downpipe, constantly monitors the oxygen content of the exhaust gas. If the percentage of oxygen in the exhaust gas is incorrect, an electrical signal is sent to the ECU. The ECU processes this information, and then sends a command to the fuel injection system, telling it to change the air/fuel mixture; the end result is an air/fuel mixture ratio which is constantly maintained at a predetermined ratio, regardless of driving conditions. This happens in a fraction of a second, and goes on almost all the time while the engine is running - the exceptions are that the ECU cuts out the system and runs the engine on values pre-programmed (УmappedФ) into its memory both while the oxygen sensor is reaching its normal operating temperature after the engine has been started from cold, and when the throttle is fully open for full acceleration.

In the event of a sensor malfunction, a back-up circuit will take over, to provide driveability until the problem is identified and fixed.

Precautions
(a) Always disconnect the power by uncoupling the battery terminals - see Section 1 of Chapter 5 - before removing any of the electronic control systemТs electrical connectors.

(b) When installing a battery, be particularly careful to avoid reversing the positive and negative battery leads.

(c) Do not subject any components of the system (especially the ECU) to severe impact during removal or installation.

(d) Do not be careless during fault diagnosis.

Even slight terminal contact can invalidate a testing procedure, and damage one of the numerous transistor circuits.

(e) Never attempt to work on the ECU, to test it (with any kind of test equipment), or to open its cover.

(f) If you are inspecting electronic control system components during rainy weather, make sure that water does not enter any part. When washing the engine compartment, do not spray these parts or their electrical connectors with water.


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