861 Fuel System Leakage

The ECM must register a fault if a leak equivalent to a hole 1 mm in diameter in the fuel tank ventilation system is detected. Figure 8.16 shows the general principle of the leakage detection system.

In addition to the normal evaporative purge control (EVAP) valve (4) there is a valve (5) that the ECM operates to control the supply of fresh air to the carbon canister and a pressure sensor (9) at the petrol tank. When valves (4) and (5) are closed, the fuel evaporation system, from the tank up to these valves, is effectively sealed. The pressure sensor (9) will register a pressure reading that will be read by the ECM. If the EVAP valve is now opened, with the engine running, the manifold vacuum will create a vacuum in the entire fuel evaporation system and the new lower pressure will be recorded by the ECM, via the pressure sensor (9). Valves (4) and (5) are again closed for a period of time during which the ECM monitors the dC

1 Air filler

2 Intake manifold

3 Induction via engine

4 Active-carbon filter (ACF) regeneration valve

5 Active-carbon filter (ACF) shut-off valve

6 Active-carbon filter

7 Fuel tank

8 Tank lid with safety valve

9 Pressure sensor

1 Air filler

2 Intake manifold

3 Induction via engine

4 Active-carbon filter (ACF) regeneration valve

5 Active-carbon filter (ACF) shut-off valve

6 Active-carbon filter

7 Fuel tank

8 Tank lid with safety valve

9 Pressure sensor

Fig. 8.16 The elements of a leakage detection system reading from pressure sensor (9). Any significant change in pressure as recorded by the sensor (9) indicates that there is a leak in the evaporation system.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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