Evaporative Emissions System: Description and Operation

The evaporative loss control system, prevents unprocessed vapour emitted from the fuel tank from entering the atmosphere.

The tank pressure control (Rochester) valve is installed between the fuel tank and the carbon canister. It is normally closed, but open during engine operation, venting the vapours from the fuel tank to the carbon canister.

The purge valve is controlled by the engine control module (ECM) and is linked to the carbon canister.

Excess vapor formed in the fuel tank is absorbed into the evaporative emission purge control canister (9). While the engine is running, the fuel absorbed in the canister is gradually purged back into the engine by manifold depression. The rate of purging is under the control of the evaporative emission purge control solenoid valves (7 and 8) which are controlled by the ECM. This helps control excess hydrocarbon emissions from the vehicle.

Fig. 1 EMS System Schematic:

1. Intake Air Temperature Sensor
2. A-Bank Air Cleaner
3. B-Bank Air Cleaner
4. Throttle Position Sensor
5. A-Bank Idle Air Control Valve
6. B-Bank Idle Air Control Valve
7. A-Bank Evap. Emission Purge Control Solenoid Valve
8. B-Bank Evap. Emission Purge Control Solenoid Valve
9. Evap. Emission Purge Control Canister
10. A-Bank Manifold Absolute Pressure Sensor
11. A-Bank Fuel Filter
12. B-Bank Manifold Absolute Pressure Sensor
13. B-Bank Fuel Filter
14. Camshaft Position Sensor
15. Engine Position Sensor
16. Engine Speed Sensor
17. A-Bank Fuel Injectors
18. B-Bank Fuel Injectors
19. Fuel Pressure Regulator
20. Fuel Tank
21. Main Fuel Pump
22. Secondary Fuel Pump
23. Fuel Level Sensor
24. Engine Coolant Temperature Sensor
25. A-Bank Ignition Amplifier
26. B-Bank Ignition Amplifier
27. A-Bank Ignition Coil
28. B-Bank Ignition Coil
29. A-Bank Upstream Heated Oxygen Sensor
30. B-Bank Upstream Heated Oxygen Sensor
31. A-Bank Downstream Heated Oxygen Sensor
32. B-Bank Downstream Heated Oxygen Sensor
33. Secondary Air Injection Pump
34. Secondary Air Injection Switching Valve
35. Vacuum Solenoid Valve
36. A-Bank Secondary Air Injection Check Valve
37. B-Bank Secondary Air Injection Check Valve
38. Ignition Supply
39. Engine Control Module
40. Malfunction Indicator Lamp / Instrument Pack
41. Battery
42. Cranking Signal
43. Security and Locking Control Module
44. PDU / Generic Scan Tool
45. Transmission Control Module (5 lines)
46. Air Conditioning Control Module (4 lines)
47. Park Neutral Switch
48. Power Steering Pressure Switch