Emission Control Systems: Testing and Inspection
EXHAUST EMISSION TEST:
Access to the engine compartment means that it is possible to check the oxygen sensing circuit without having to open the engine compartment.
For this purpose, a 6-pole plug connector is installed on the relay mount 2 in the rear luggage compartment (direction of travel: left). If terminal 2 and terminal 1 are connected, ground is applied to the DME control unit output terminal 42 thus triggering the test.
During testing, the tank venting valve is first actuated. The precontrol factor for the injection map is adjusted by an appropriate amount towards "lean" and the oxygen is simultaneously frozen for a short period of time. If the exhaust gas is measured in the end pipes, it is possible to detect an increase in the oxygen factor in the exhaust gas. When the precontrol has been adjusted and the oxygen regulator has been frozen for a short period, the oxygen regulator then starts and again compensates the adjusted precontrol (the oxygen display in the emission tester returns to the tolerance field). If the plug bridge is now removed, the precontrol factor is again set to its initial value and the oxygen regulator is again frozen for a short period of time. Since the oxygen regulator has been adjusted towards "rich", the mixture is now too rich (can be measured using the exhaust emission tester). After a short time, the oxygen regulator returns to its average value and the test ends.
The engine speed signal is applied to terminal 6 of the 6-pin plug.
The test can be started when the following operating conditions apply:
- No faults in the engine temperature measuring circuit
- No functions activated with the Porsche System Tester 2
- Idle speed
- Oxygen regulators 1 and 2 active
- Engine temperature > 60°C
- Time after engine start > 30 seconds
The time factors programmed for testing the regulation circuit are selected such that the time intervals required by law for the exhaust emission tests (correction of incorrect values) are observed.