'Howling' noise at startup? AIR/Emissions?

[SNaray8442]

After the car's been sitting for some time, it "howls" for a few minutes at startup. Seems like it's coming from the device to the rear driver's side of the engine bay. Is that the AIR/EGR system? Is this noise a problem?

[PTEC]

Yep thats the secondary air pump. Perfectly normal.

[SNaray8442]

It's so loud, though.

I've never had a vehicle's AIR make so much racket.

[jamesgood72]

What does this secondary air pump do? I've wondered what that sound was coming from too. Takes a minute or two to go off on my 99 C2.

Thanks,

-James.

[Loren]

What does this secondary air pump do? I've wondered what that sound was coming from too. Takes a minute or two to go off on my 99 C2.

Thanks,

-James.

More than you likely 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 4.7 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]

Blows fresh air in to the exhaust for pollution reasons, oxygen dilute the exhaust gasses.

[SNaray8442]

Loren, I come from the "muscle car" world originally where AIR/EGR was removed quite regularly to unleash horsepower. Do you think these cars will yield a noticeable difference with emissions disabled?

[Loren]

Not really - like the quote says that pump runs for a max of 179 seconds (just under 3 minutes).

These engines are already putting outs lots of HP/liter as it is. (IMHO) With late model Porsche's there is not much to be gained with mods. If you want a lot more power you move up to a GT3 or TT.

The TT responds pretty well to specific mods - but then you have to ask yourself if you really need 750-800 HP (and can handle it).

[jamesgood72]

Thank you for the detailed information Loren. That's great info. I like to know what my car is up to... :)

-James.

[PTEC]

Loren, I come from the "muscle car" world originally where AIR/EGR was removed quite regularly to unleash horsepower. Do you think these cars will yield a noticeable difference with emissions disabled?

Im not really a muscle car guy but I believe the old smog pumps were driven by the fan/accessory/serpentine belt and thats why they were removed to 'gain' power. The boxsters system is basically an electric fan, so removing it would do nothing for you other than make a nice check engine light pop up.

[flyingpenguin]

I have a similar howling / squealing problem at cold start-up (and cold-start-up only). My Durametric indicates that there may be a vacuum leak on bank 2 (RKAT adaptation values are off: 0.19 for bank1 and -0.28 for bank2).

The folks at Durametric have been very helpful pointing out possible sources of the vacuum leak:

1. Spark plug tubes

2. Oil/air separator

3. Oil air separator tub that runs to the opposite side of the block.

4. Intake manifold above alternator

I have the following questions:

(1) Is this list of causes exhaustive?

(2) Where can I find any procedures/steps to verify/exclude any of these causes?

Your insights are much appreciated.

Rgds, Joost

2000 996 C2 (USA)

[flyingpenguin]

I should add that my engine is almost new: it was replaced in August 2006 and has approx. 20K miles on it since replacement.

[violaGT3]

Loren, I come from the "muscle car" world originally where AIR/EGR was removed quite regularly to unleash horsepower. Do you think these cars will yield a noticeable difference with emissions disabled?

Im not really a muscle car guy but I believe the old smog pumps were driven by the fan/accessory/serpentine belt and thats why they were removed to 'gain' power. The boxsters system is basically an electric fan, so removing it would do nothing for you other than make a nice check engine light pop up.

Hey I'm an old muscle car guy and the point of pulling all that mess out was to stop the vacuum loss in the system. All the crazy little hoses and valves and bypasses really did a number on tuned carbs.

Anyways has anyone ever replaced it to see if it is just a worn out thing? My 99C2 does it but my 03GT3 does not.

[flyingpenguin]

Update:

Turns out that the squeal at start-up was caused by the starter. I took it out and took it apart. The bushing that's holding the axle at the back end was not lubricated anymore.

A little high-temp grease fixed the problem.

JP