Secondary Air System & Cat Bypass Pipes

[ivass]

I am considering cat bypass pipes and wanted to know if anyone has looked at the secondary air pump when installing those. Based on the below info posted by Loren in the 986 forum, looks like the air pump runs from about 1 to 3 minutes after a normal start up. If I am not mistaken the duration is determined by the ECU based on data from the secondary O2 sensors (is this correct?). If this is the case, does that mean that the pump will run for the full 179 seconds with by-pass pipes? Also, does anyone know if the operation of the pump is affected by switching from OBD2 to ROW DME? Am I overlooking anything?

I would appreciate any input.

Ivo

The below was posted by Loren in the 986 forum!

Per Porsche's 199 Tech Book...

"Auxiliary Air Pump

To reduce pollutants contained in the exhaust gas during the warm-up phase and to achieve the emission limits of the roll test in the USA, USA vehicles have a secondary air system. For this reason, an electric air pump has been mounted on the left-hand side of the engine compartment (Carrera). This pump is activated by the DME control unit and blows the additional air through air ducts to the discharge valve. A pneumatic switching valve which is closed when the secondary air system is inactive thus preventing the flow of additional air is installed between the air pump and the discharge valve.

Functioning

If the engine is started in a temperature range between minus 10.5° C and plus 45° C, the secondary air system is activated for a period of time dependent on the start temperature (min. 50 seconds, max. 179 seconds).

The secondary air system is only activated if the following engine-related operating conditions apply:

- Engine load (TL) between 0.7 ms/rev, and 4.7 ms/rev.

- Air mass (ML) not greater than 300 kg/h

- Engine speed between 680 rpm and 2,800 rpm

- Altitude adaptation factor greater than 0.76 corresponding to less than 2,400 meters above sea level."

[RFM]

Engine temperature is the responsible data for second air pump as Loren said. ROW cars have the same pump, a switch from USA to ROW have no influence to the pump IMHO.

[tholyoak]

Switching the DME to the ROW (EU2) program will result in the DME ignoring the secondary air system. It is not present on the cars from the factory in EU2 countries.

-Todd