My CTT is 2008, with 65,000 miles on the clock.
Recent maintenance included new spark plugs and new coils after a 'misfire cylinder 8' error a couple of months back.

Now a new issue develops. The best I can explain it is this: when I 'engine brake' (lift my foot off the accelerator while in gear, such as when going down a hill) and at the bottom of the hill I get back on the gas, there is a brief hesitation followed by a huge bellow of blue smoke from the exhausts. Every single time. It's as if the 'under-pressure' during the engine braking forces/sucks oil into the combustion process (I'm no mechanic, so forgive me if this sounds ignorant).

This results is an oil consumption of 2 quarts per 500 miles when driving in hilly country.

There are no error codes.

Any idea what I am looking at? Is this something that could be caused by a defective/leaky air-oil separator? Something else?

​​​​​​​Any suggestions are welcome.
(also asked this question on Rennlist)

 

You may have a bad PCV check valve. The orange diaphragm inside gets "scalloped" edges, due to globs of hot oil sludge passing through. While you are at it - check inside the Air-Oil-Separator outlet tube for oil film. It should be dry. Engine braking causes excessive positive crankcase pressure and if the valve seals are too far gone - the blowby will force oil thru the piston rings, and burned via the intake.

Shoot Berrymans B12 Chemtool inside the AOS outlet hole and also soak the PCV thru all 3 openings. Visually inspect that any of the PCV diaphragm is not damaged. You can quickly "repair" the scalloped edges, by blowing thru the PCV check valve in the opposite direction of flow. At the very least... you will be needing a new PCV check valve.

 

Thank you sir,
Do you happen to know where I might find the part number for this 2-way PCV valve?

Thanks again for the input.

 

I'm sorry, in your model - it's built into the intake runners...

 

So I had the Air-Oil separator and some intake valve replaced. The guys over on the other Porsche forum mentioned checking the intercooler on the driver's side and the pipe connected to it and to clear any accumulated oil from there. My indy ignored it and sure enough, the same billowing blue smoke upon re-acceleration after braking on the engine.
Took it back, they checked the intercooler and the pipe (and admitted there was 'quite a bit of oil in there'). All good now. No more smoking and car drives well again...

 

I say 95% of the time - 955/957 oil consumption is due to lousy design of PCV and AOS system... not valve seals, not piston rings(if compression good), not turbos... but accumulated oil vapor blow-by!!!

 

I think you're correct since they finally sorted it out on the 958 CTT around mid 2013.. and the retrofit AOS on the earlier 958 turbos cured oil use for sure.

I have the service records for mine from the 1st owner. She took it into the dealership about once a month because the low-oil warning was on. It usually took 1-1.5 liters. This was like clockwork.

Finally, in 2013 they replaced the AOS with the new design one - and oil use simply stopped. It now uses about 700CC between 5,000 mile oil changes. That's acceptable to me. And it never blows smoke out the rear. When the engine was out for some work due to a dealerships screwup, I purposely took a look at both pipes running to the intercoolers. Nothing in either one - spotless. No sign of oil at all.

It's a shame they never made a retrofit for the earlier ones, but since most of it is cast into the valve cover my WAG is it isn't possible without redesigning the valve cover - and that's not going to happen on an engine out of production for 8 years.. On the 958 V8 engines, the AOS is a plastic goober (tech term) bolted to the drivers side valve cover. It's easily replaceable. On your earlier ones - a catch can sounds like the only reasonable answer. Maybe some aftermarket guy can come up with one that has an automatic scavenger pump that returns the collected oil to the sump..

 

Yep, Catch Can is my solution. Until I can review all the available options out there... I will continue pouring oil into the Pig.

 

+1


I have a Mishimoto Catch Can kit sitting in the garage - just need to find time to do the install - maybe a winter project.

 

Would you mind documenting your install with photos please? I'm having what I would consider excessive oil consumption. About a quart every 2,000 miles or so.. Running 0W-40 (oil was originally done at my local shop with Motul, but been adding Castrol with the Porsche spec on it as I can find it locally)

 

Sorry, I never got around to doing this and sold the catch can to a different Cayenne member on Rennlist. Figured I'd buy another one when I had time to do the project or maybe do a complete AOS that recycles back to the oil pan as a closed, zero-maintenance system like I did on my supercharged 928 using a compact Verus dual-chamber AOS that works great.

I can tell you though, that the absence of a catch can is not the cause for your excessive oil consumption. My 09 CTTS uses absolutely 0 oil between 5,000 mile change intervals without one and the stock crankcase vent back to the driver's side intake plumbing. On my next oil change I plan to pull the DS intercooler to see how much I've accumulated in there and that might move an AOS install up the priority scale. What the catch can does is allow any oil vapor that would normally condense in the driver's side intercooler to accumulate somewhere else (the catch can) where emptying it is easier and doesn't impact intercooler performance.

If you're using a quart of oil every 2,000 miles you likely have a ring seal issue and significant blowby past the piston rings. What do your spark plugs look like and do they all look the same or are some fuzzier and sootier than others - those would be the ones with the oil contamination on them.