Daza

Hi recently bought a Cayenne S '08 so I a new to the forum and new to Porsche.
It just hit 100k miles and it started to give white smoke upon start up. I also had a CEL come on every 200 miles or so with the fault "P0431 Warm up catalyst efficiency below threshold bank 2" which I could reset using a foxwell. The white smoke has being getting worse and a shuddering/stuttering can be felt if i try to slowly accelerate in and around the 30 - 40 mph range, mainly if i come off a highway and coast, slow down and then try to drive at a steady speed. Car stutters almost like a slight misfire and a cloud of white smoke bellows briefly.
I am guessing the AOS is defective? I don't have a manometer handy, but i did check the oil filler cap and there is a 'good' vacuum when car is running.
I have ordered a new AOS ($140) and will attempt to replace it, is there any advice or videos on doing this replacement. I have seen the write up on Pelican parts but looking for some more.

Thanks in advance.

http://www.pelicanparts.com/techarticles/Porsche-Cayenne/67-ENGINE-Repairing_the_Air-Oil_Separator/67-ENGINE-Repairing_the_Air-Oil_Separator.htm

Mani Man

Shawn Stanford

Stuttering at low speeds sound like coils. How many miles on your current coils? Have you smelled the exhaust cloud to see if it is oil or unburned fuel?

Mani Man

Shawn Stanford

I don't recall the AOS being a common problem on Cayennes. That shouldn't cause grinding, in any case.

I see you have an 'S'. Any chance the smoke is blow-by due to cylinder scoring? How does the oil look?

NelaK

How recently did you buy the car? Was it from a dealership? Because if its from a dealership and you have any chance at all of returning it - do so ASAP. Even if it costs you a bit of money.

Replacing the AOS is pretty straight forward. While you have it and the associated plumbing apart, its worth while to give the PCV valve an inspection to make sure its also good. If you look at the parts diagram, its right on the front of the engine. Super easy to access.

As for the code - if the car is burning excessive amounts of oil, its entirely possible for that to cause issues with the catalytic converter and for that to trigger a code like that.

You should also pull out your ignition coils and spark plugs and inspect them. If the coils are bad, the casing is often cracked (not a guarantee that bad coils will be cracked though).

If I had to guess, whatever is wrong has been wrong for a while. The previous owner likely noticed the issue when it first started but wasn't severe enough to be easily noticeable. They probably didn't address it because of cost and instead chose to sell the car before things got too bad. As a result, the engine has been having issues for long enough that the catalytic converters are possibly damaged. Cylinder scoring is a sad but very likely possibility.

Mani Man

Hi,
I’ve just bought the car from
a car dealer. I showed him the smoke as per him it’s just some “junk” from exhaust which should clear up after some drive. I driven it about 200kms still it’s the same and now he says it could be breather hose issue and he will replace it. Shouldnt the smoke be white-ish if it was AOS issue? Mine is more blueish and smells a bit like oil. How do I check for cylinder scoring cos. I do sometimes feel some short vibrations even while idling. Oil level was a bit low I’ve topped it up will continue to monitor if it’s eating it up. Pls advice what should I do?

-~TIA

MANI

Wisconsin Joe

Is the motor knocking at all?
There's typically a bit of ticking from the injectors, but if there's a deeper knocking sound, then the motor is likely junk.

As suggested above, return the car and get your money back.

Mani Man

Hi,

Thanks for your reply.

ok here’s how the engines sounds like. In first video there’s a bit of “hissing” sound and after a while I started hearing a clicking and a whistle kinda sound.
The car dealer won’t take it back that easily unless I have solid proof engine is junk.

Video -1

Video-2
TIA.

~Mani

Vivid7

that doesn’t sound like scoring. It is too high pitched. the scoring sound is a cha chunk sound. down stroke and up stroke noise. Thats just a single tick sound.

AOS his hissing like crazy. I’d bet it has a rip in the diaphragm or you have a intake vacuum leak somewhere.

Mani Man

Hi,
Thanks for your quick reply, you guys are just great. Is there a way to find where the vacuum leak is ?

~Mani

NelaK

Spray bottle with soapy water could work. It'll bubble where there's a leak or you might notice an immediate change in how the engine is performing.

Start with the AOS since that's the most likely.

Mani Man

Hi,

Did you get a chance to listen to this “huffing” sound just as I give it a little throttle?


Is this also a leak somewhere ?

~Mani

NelaK

I think the AOS is more of a constant hissing sound. It sounds like what you're hearing in the first video.

I'm not sure what's causing the huffing maybe someone else can identify it. It could also just be the AOS too as the vacuum changes.

Just thinking through it though - it appears to happen just before the RPMs increase so I might take a look at the intake piping. It could be something as simple as the air filter boxes not properly being sealed.

You should definitely remove the beauty covers and just stick your head in the engine compartment to see if you can isolate a general area. One thing I like to do when trying to locate odd sounds is to try wearing noise cancelling headphones or ear plugs. They can often block different frequencies of sound, making it easier to isolate the particular sound you're looking for. I don't know if it'll work for these particular sounds but I find my bose headphones are great for blocking out the normal engine rumble so you can focus in on the higher frequency ticks and rattles.

DHC8FO

We are starting to make a repair kit for these. I'd be happy to give out one or two to someone who has this failure to test and give us some feedback.