Jump to content

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

high pitch humming sound at startup


Recommended Posts

I recently purchased a 1999 996 C2. When I start the car after it has not been driven for a few hours, there is a high pitch humming sound that lasts for about 30 seconds and then shuts off. After browsing the forums for a while, I am under the impression that it is the secondary air pump. Is this how the pump is supposed to sound? It seems rather loud and is kind of annoying. Any suggestions?

Thanks.

Link to comment
Share on other sites

  • 1 month later...
  • Admin

Here is more than you probably want to know:

"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. 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 4.7ms/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."

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.