Exhaust System: Testing and Inspection

Exhaust system, checking for leaks
^ Start engine and run at idling speed.
^ Plug the tailpipe (e. g. with rags or stoppers) and leave plugged until the check is complete.
^ Listen for noise at the connection points (cylinder head/exhaust manifold, exhaust manifold/turbocharger, turbocharger/front exhaust pipe etc.) to determine whether there are any leaks.
^ Repair any leaks that are found.

Secondary air system, components and function
The secondary air system results in quicker heating and therefore earlier operating readiness of the catalytic converter representing a cold start.

Principle
Due to over - enrichment of the mixture during the cold start phase, there is an increased amount of uncombusted carbon monoxide in the exhaust. Secondary Air Injection (AIR) improves secondary oxidation in the catalytic converter and therefore reduces emissions. The heat produced by secondary oxidation greatly reduces start - up time for the catalytic converter, therefore improving exhaust quality during the cold start phase significantly.

Function





^ After cold start, the ECM - 2 - starts the secondary air pump - 12 - via the relay for Secondary Air Injection (AIR) - 1 -. Air is blown to the mechanical secondary air valve- 10-.
^ Parallel to this, the Secondary Air Injection (AIR) solenoid valve - 3 - is activated, which permits negative pressure to reach the mechanical secondary air valve - 10 -and the pressure unit for boost pressure regulation - 7 -.
^ The mechanical secondary air valve thereby opens the path for secondary air to the exhaust channels of the cylinder head.
^ To prevent unnecessary heating, secondary air is led around the turbocharger. For this, the boost pressure regulation pressure unit opens the boost pressure valve. The pressure unit, designed as a double reservoir, has a vacuum connection for this on the intake side.

1 - Secondary air injection pump relay - J299
2 - Motronic engine control module - J220
3 - Secondary air injection solenoid valve - N112
4 - Intake manifold
5 - Check - valve
^ Installation position (light/dark side): Arrow points in direction of flow as shown in diagram
6 - Vacuum reservoir
^ Mounted at cylinder head cover
7 - Pressure can for boost pressure regulation
8 - Turbocharger
^ Checking turbocharger, Refer to Powertrain Management.
9 - Cylinder head
10 - Combination valve
^ For Secondary Air Injection (AIR)
11 - Air filter
12 - Secondary air injection pump motor - V101