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Discussion summary
YOUR RESEARCHPlease help me troubleshoot this... :(
Leading reported evidence
Replace aos about a year ago
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
Other owner said that he replaced the AOS about a year ago.
Leading evidence: 'Replace aos about a year ago' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'sticking variocam adjuster, probably' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check leaking fuel injectors' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
Supposedly the AOS was replaced about a year ago by some indie that was not necessarily a Porsche specialist.
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Performed · outcome unconfirmed · Original poster
Drove it hard at my autox venue for about 2 hours and used about 1/2 qt.
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Discussions that suspect a cause
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Suspected cause
The P0016 is likely a sticking variocam adjuster, probably from a little trash in the adjuster that may work its self out .
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Suggestion
You will not loose any sleep over aos failure (UAOS diaphram is 2x thicker than AOS and Motorsports AOS), nor overfilling your oil (can handle 1qt over full), nor intermix (no more cooling running thru aos), nor the high cost of having to replace the brittle oem AOS when it fails again (10 min diaphram replacement).
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Suggestion
The P0421 is a failing cat possibly from burning a little to much oil...Replacing the cats with high flow cats will solve it, or installing some mini cats possibly will solve it at a much lower cost...
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Suggestion
First thing first :: lets see just how good a shape the piston ring seal is....I suggest you run the "blow-by test" that I designed for us to evaluate the ring seal and engine health...
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36 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261027T201111Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
@TexSquirrel
@Porschetech3
Please help guys!
3.8 liter Flat-six Innovations Stage II engine with about 22K miles since the rebuild by Raby in 2014. Car was shipped to them and Raby broke the engine in.
When I start it I get blue smoke for about 2-3 seconds.
Drove it hard at my autox venue for about 2 hours and used about 1/2 qt. of oil. No visible signs of oil leakage.
Put this cardboard behind the car on a cold start - notice the big specs of black. After warm up it doesn't do this.
Almost every time I cold start the car I get these three codes, clearing them right away and they don't return the rest of the day, no matter how hard I drive the car.
Stored - P0421 Catalyst 1 Efficiency below Threshold Bank 1
Pending - P0421 Catalyst 1 Efficiency below Threshold Bank 1
Pending - P0016 Crankshaft Position - Camshaft Position Correlation Bank 1 Sensor A
Here's pics of the exhaust residue and the codes:
It's installed in a 06 Cayman S with a Carnewal Modified Exhaust. The guys at Carnewal say the cats are most likely toast causing the cat errors, and a set of their high flow cats will fix that.
See the black specs? Zoom in...
P0421 Stored
Assume you bought it with the Raby engine previously installed? When my 996 was spitting black stuff out the drivers side exhaust it was one of the death signals for bore scoring. Jake fixed that for me. I never got cat warnings. I got misfire codes on 5&6 cylinders because they were bridging with soot & oil. However, oil will kill a catalytic converter.
First thing first :: lets see just how good a shape the piston ring seal is....I suggest you run the "blow-by test" that I designed for us to evaluate the ring seal and engine health...
The thread that shows how to do this simple but extremely valuable procedure is here..
https://rennlist.com/forums/996-foru...+engine+health
Do you have the UAOS on this car? I also suggest you test AOS function while you are testing the blow-by..
After we know the results of these test, I can give a much more precise evaluation/diagnosis of exactly what is going on...
The P0421 is a failing cat possibly from burning a little to much oil...Replacing the cats with high flow cats will solve it, or installing some mini cats possibly will solve it at a much lower cost...
The P0016 is likely a sticking variocam adjuster, probably from a little trash in the adjuster that may work its self out . I would change the oil a couple of times and monitor this before going in to replace the adjuster...
BTW :: the wet spot on the cardboard is just water...13% of all combustion by-products is water/water vapor( h2o)...for every gallon of gasoline burned, there is one gallon of water produced, and the little black dots are carbon from the oil being burned...
My guess is AOS is causing smoke.
Cats likely need replacing.
I would also check for leaking fuel injectors.
That can cause cats to fail and bore scoring to accelerate.
OP - If FSI broke in the motor, highly doubt ring seal. AOS possible. AOS can fail if you look at it wrong. Injectors possible. Oil sample would show high fuel dilution. Sensor may be bad. Broken wire will cause it. Something may have caused one cat to go bad, but �what� is the $25,000 question. You can pull the cat and put an eyeball on the core.
Yeah, I would test your oem AOS with a manometer. May be something else, but it's worth it to test your AOS nevertheless. They are as brittle as thin ice.
I have been thru 2 oem AOSs and 1 motorsports AOS. Imho the UAOS track version, even if you don't track your car is the way to go. You will not loose any sleep over aos failure (UAOS diaphram is 2x thicker than AOS and Motorsports AOS), nor overfilling your oil (can handle 1qt over full), nor intermix (no more cooling running thru aos), nor the high cost of having to replace the brittle oem AOS when it fails again (10 min diaphram replacement).
This not to stoke the usual "they suck to expensive conversation" However I thought the value prop with fsi was a bullet proof engine. So how would you get scoring on an engine with 22k miles? What am I missing?
Doubt you are missing anything. Likelihood is very small with nickies. But you always have a PO owner that doesn't do what they are supposed to do and mucks it up. Rennlist is a digital advertisement for it. WAG says it's the AOS if anyone is taking bets.
thats what I thought as well "Smoke is gone today drving to work" without fixing it or knowing why=bad idea. I would not even do that with a honda because i don't want to spend time standing on the side of the road, but not my car or time so 🤷♂️.
Is the track UAOS the one that Porsche tech produces?
Other owner said that he replaced the AOS about a year ago. I do realize they fail even brand new ones.
My plan is to order the track version uaos and replace it myself. That's going to be quite a job with the full roll bar on this car. But I know it's doable.
Thanks for all the inputs everybody! I really appreciate it! I will also use my manometer to verify that the aos is okay. I did that before I purchased the car and it seemed okay to me but I'll double check.
Yes it is.
With the 986/987,996,997.1, all we have to do is run a more durable AOS and IMSB, keep our water pump and fuel injectors fresh, and run top oil and keep it fresh and we mitigate alot of catastrophic issues in the cars. Yeah, I know, there is always an exception to the rule, but these cars are so easy to strengthen and elongate the life of an M96/M97.
Congrats on your FSI Cayman. I would love to find an FSI 996 Cab for my wife one of these days.
You should check with LN on what the manometer should read. Jake referenced that his engines would not have the same results vs a stock engine.
Good luck with the new car.
My suspicion is that whatever is causing this
P0016 Crankshaft Position - Camshaft Position Correlation Bank 1 Sensor A
caused your cat failures. I wouldn't change the cats until you solve that first.
FSI engines with stock AOS will have the same manometer readings as all other engines with stock AOS ( 4-6" H20)... UAOS will read 1" H20 "lower" on any engine...
He was referencing the "blow-by readings": ( using a manometer) on FSI engines would be different than stock engines due to different "ring package and cylinder finish"..
@Porschetech3
Okay, here's the video with the manometer reading. Car was fully warmed up, just drove it home from work. Note the sound of the starter...thanks to the wifey for starting the car!
Also, submitted a Flat-six ticket with this video.
You Tube
Raby's response:
Those readings are low at idle. This would generally indicate a crankcase vacuum leak, not a bad AOS. The AOS failing will cause high vacuum, over 6”.
I’d look for a vacuum leak, or maybe the fueling is over- enriched causing a loss of ring seal.
Jake is correct, "high" readings will always be a bad AOS..."low" readings can be a vacuum leak OR a weak ring seal...hence the need to test "blow-by" to see the exact actual value in Liters per minute..
Never say never (or dont). I have have seen several mezger engines in the past few years on this board with bore score. Its a very low percentage and its hard to do but it can happen. Just my $.02.
I'm going to try and do a smoke test this week before I autox on Saturday. Hard part is removing the roll bar to get at the engine cover...to be continued...
Raby's response:
"Crankcase vacuum leaks are the primary cause of over fueling. If the vacuum is low the engine will over fuel to protest the environment by making the cats work harder. I’d smoke test the entire engine and look for leaks.
Caymans are bad about the crossover EVAP hose cracking near the bank 2 cylinder head.
If the engine runs over rich long enough the cylinders glaze. If you have more than 1k miles on the oil and it is jet black when drained, then you have soot in the oil from poor cylinder seal. There’s not really any way to overcome this at that point.
If you do not find any leaks we could try a tube to lean it out."
Jake said, "
Caymans are bad about the crossover EVAP hose cracking near the bank 2 cylinder head."
Please show me (red arrow would be nice) what hose he's talking about in these pictures?
Thanks!
Don't know nuttin' about a Cayman engine, but shouldn't there be a hose on the bottom right of that device in photo #3. Sure looks like there "was" to me...
The breathe hose Jake is talking about is the one shown with white arrow and red arrow, it attaches to the bank 2 side near the intake #4 runner by the A/C ..
The top red arrow is pointing to the breather hose from AOS to plenum, looks to be wet with oil, and that looks like an after market plenum and non-OEM hose..
Sure looks like the AOS is failing OR the ring seal is not good...
But you can smoke test to rule out vacuum leaks at the crossover breather hose...
That top AOS breather hose doesn’t look anything like the OE version. There should be zero oil film there. On my 996 I had a slip connector not seated (where you have oil collecting on yours) and smoke test confirmed it. FCP has the correct breather hose for $72.
I’m curious why that line would be hacked up in the first place. Doesn’t seem like a Raby original production that.
Supposedly the AOS was replaced about a year ago by some indie that was not necessarily a Porsche specialist. I was in there playing around yesterday tightening everything up and the clamps for that hose you're talking about were loose, I tightened them up started the car, no smoke everything seems to be good now we'll go test it out later today.
