percentage of the available time for which the device is energized, as shown in Fig. 1.17.

The performance characteristics of the engine and the driveability of the vehicle are determined by the 'quality' of the input that is put into the design, and part of this design is the computer program that is held in the read only memory (ROM) of the ECM. A fuelling map is similar to the ignition map shown in Fig. 1.4. The differences being that engine load is represented by throttle position and spark advance is replaced by air/fuel ratio. Each point of the surface on this map can be represented by a binary code and a range of points from a map is stored in the ROM of the ECM. The values stored in the ROM are compared with input signals from sensors in order that the computer can determine the duration of the fuel injection pulse.

Some computerized systems are designed so that the franchised dealership can alter the computer program to match customer requirements. A re-programmable ROM is necessary for this to be done and the work can only be done by qualified personnel acting under the control of the vehicle manufacturer.

Multi-point injection systems commonly use one of two techniques.

1. Injection of half the amount of fuel required to all inlet ports, each time the piston is near top dead center.

2. Sequential injection, whereby injection occurs only on the induction stroke.

In the multi-point injection system shown in Fig. 1.18 there is one petrol injector (number 12 in the diagram) for each cylinder of the engine. Each of the injectors is designed so that it sprays fuel on to the back of the inlet valve. The actual position and angle at which injection takes place varies for different types of engines.

In the system shown in Fig. 1.18 the air flow is measured by the hot-wire type of mass air flow meter. The control computer receives the signal from the air flow meter and uses this signal together with those from other sensors, such as engine speed, engine coolant temperature, throttle position etc., to determine the length of time of the injection pulse.

Sequential multi-point injection is a term that is used to describe the type of petrol injection system that provides one injection of fuel for each cylinder during each cycle of operation. To assist in providing the extra controlling input that

1. EEC IV module

2. In-tank fuel pump

3. Fuel pump relay

4. Fuel filter

5. Idle speed control (ISC) valve

6. Mass air flow (MAF) meter

7. Air cleaner

8. Fuel pressure regulator

9. Fuel rail

10. Throttle position sensor (TPS)

11. Air charge temperature (ACT) sensor

12. Fuel injector

13. Camshaft identification (CID) sensor

14. Carbon canister (EVAP)

15. Purge solenoid valve (EVAP)

16. DIS coil

17. Battery

18. EDIS-4 module

19. Engine coolant temperature (ECT) sensor

20. HEGO sensor

21. Crankshaft position/speed (CPS) sensor

22. Power relay

23. Power steering pressure switch (PSPS)

24. A/C compressor clutch

25. Service connector (octane adjust (OAI)) (plug-in bridge during production for operation with Premium RON 95 unleaded fuel

26. Self-test connector

27. Diagnosis connector for FDS 2000

28. Ignition switch

29. Inertia switch

30. Electronic vacuum regulator (EVR)

31. EGR valve

32. Differential pressure transducer (DPFE sensor)

33. Differential pressure sampling point

34. To inlet manifold (air chamber)

35. Pulse air filter/valve housing

36. Pulse air solenoid valve

37. A/C radiator fan switching

38. Electronic transmission control (CD4E)

Air intake - atmospheric pressure Air intake - inlet manifold pressure Hi Fuel supply - system pressure

Fuel supply - low pressure Exhaust gases ahead of catalytic converter ^ Exhaust gases after catalytic convertor

Fuel vapour

Fig. 1.18 A multi-point petrol injection system is required for sequential injection the engine is often fitted with an additional sensor which is driven by the engine camshaft. Hall type sensors and variable reluctance sensors driven by the camshaft are often used for this purpose to assist the computer to determine TDC on number 1 cylinder. Figure 1.19 shows one of these sensors which is fitted to an overhead camshaft engine.

Some of the sensors used for fuelling are the same as those used for ignition systems, e.g. crank speed and top dead center sensors, manifold pressure to indicate engine load etc. Because some of the sensor signals can be used for both ignition and fuelling it has become common practice to place them under the control of a single computer and the resulting system is known as an engine management system.

1.5 Engine management systems (EMS)

Engine management systems are designed to ensure that the vehicle complies with emissions regulations as well as to provide improved performance. This means that the number of sensors and actuators is considerably greater than for a simple fuelling or ignition system. The system shown in Fig. 1.18 is fairly typical of modern engine management systems and selected items of technology are now given closer attention. The aim here is to concentrate on the aspects of engine control that were not covered in the sections on fuel and ignition systems.

The first component to note is the oxygen sensor at number 20. This is a heated sensor (HEGO) and the purpose of the heating element is to bring the sensor to its working temperature as quickly as possible. The HEGO provides a feedback signal that enables the ECM to control the fuelling so that the air-fuel ratio is

Fig. 1.19 A cylinder identification sensor

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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