mark944turbo

Hello, I have not been on the forum for a while, but used to frequent the 951 section years ago.

Now having some problems with Check Engine Light on a 2012 Cayenne S. Here are the codes that come back pretty quickly after clearning:


I figured a vacuum leak (?) but didn't find anything obvious. Removing a cap from a vacuum line makes a hissing noise and an obvious vacuum leak noise:

Same with removing the oil cap. Engine speeds way up and sucks air in dramatically. Is this normal?

The "airflow when engine running" parameter looks pretty normal when idling and pressing the throttle a little (shown), and also when driving.
But the "correction factor" sounds maybe high at -23%? What does that mean?

Anything else I could check? Thanks!

Quadcammer

Unless I'm an idiot, I'm 99% sure the 958.1 cayenne S does not have a maf, but rather a map (running speed density basically). I'm guessing that code reader is giving you generic, not manufacturer specific codes.

A 23% correction means that its either adding or deducting 23% of the expected fuel. Generally with vacuum leaks it adds fuel to correct a lean a/f.

Sounds likely you have a vacuum leak. take a look at this thread:

https://rennlist.com/forums/cayenne-...ottle-pos.html

RAudi Driver

1234567890

mark944turbo

That's right- no MAF sensor but the ECU is still calculating a mass airflow value, and that's what's being displayed. I think it is Porsche specific as I have the Porsche package for this scanner.

Since I have had no luck finding a vacuum leak, I will try observing the MAF and "correction" values when I add even more vacuum leak. Hopefully that will confirm I have one, then at least I know I'm not looking for something that does not exist.

Thanks for the tip

mark944turbo

The problem was a VCT actuator solenoid, passenger side. It was easy to replace once valve cover was off. The aluminum bolts used all over this engine are ridiculously stupid, but I digress..
There was no code for the solenoid, just the P0068 and P1070. But I did recall from about a year ago seeing a code for slow response of the camshaft, which was the hint. I figured that if the camshaft was not adjusted correctly, it may influence the amount of air ingested at idle (and manifold air pressure) vs. what the computer predicts at a given throttle position. It looks like that was the case, since the code has not returned after a few days of driving, and I changed nothing else.

RAudi Driver

Is the car reading green ready light yet. If so, great work!

deilenberger

Great catch. If you check it for expected cam timing advance vs actual cam timing advance - how does it do?

BTW - the reason for the aluminum bolts is to avoid electrolysis and corrosion. Lots of the engine is made of magnesium - and magnesium combined with aluminum and steel don't play well together.

mark944turbo

I spoke too soon, codes are back (no VCT code, but the other two). My next step is to replace the MAP sensor, only because it's cheap, not because I think it will make a difference. A new throttle would be a bit more. After that, not sure what to try next. I still feel that it's a vacuum leak, but haven't had any luck finding it. Perhaps a professional smoke test..

That makes sense about the magnesium. I've replaced a few of the bolts with steel, as I think the risk is smaller than the pain caused by often-broken, dealer-only bolts on semi-frequently removed components.

mark944turbo

Some more progress: I pulled the intake manifold and found dirty intake valves. 170K miles, not sure when they were last cleaned. I did the best I could to clean without a walnut blaster and was hoping that would fix the Check Engine Light.


I could imagine a restricted intake causing low MAF value . No luck though, same codes returned.

Here is a MAF and correction factor summary since I started troubleshooting:

Does anyone know what's typical for these values on a car without Check Engine Light?
Interesting that adding an intentional leak by uncapping a vacuum line moves the correction factor back towards zero. The change was not much, but it was repeatable in back to back tests with cap on/off.

deilenberger

When you found the bad Variocam solenoid - did you clean it or replace it? And did you look down the hole it goes into on the head to see if there was a screen there? Those have been known to plug up with gunk (wouldn't be a surprise at 170k)..

You did a nice job cleaning the valves. Walnut blasting wouldn't have made it much better. What did you use?

BTW - on the turbo there are two MAP sensors, one on the front, one on the back on the starboard side IIRC. As far as I know they're identical (and if you shop using the Bosch PN on them - as cheap as about $5 each for the ones Bosch made for Chevy..) The throttle bodies are amazingly cheap (at least the turbo ones) I've seen them listed new for under $100 - usually a part like that on a Porsche is in the $500 price range. Must be used on some cheap car somewhere. Have to shop it by the Bosch number again I guess.

mark944turbo

Hi Don, I replaced the solenoid, it was about $350 from the dealer. The screens on the old one were intact and no debris. I did not look down the hole for an additional screen, but hopefully the lack of VCT related codes means the new solenoid is working ok.

These photos summarize the cleaning process I used


Basically: warm up engine, remove manifold, spray the valves which are fully closed so nothing can leak into cylinder, scrape with long picks/o ring tools, power scrub with brush on drill, vacuum out, repeat until satisfied.
Then rotate the engine until the remaining 2 cylinders have closed valves. Repeat for those two cylinders.
On startup, there was a bit of smoke or maybe 20 seconds, then it cleared right up. The directions on the can were different and involved spraying into a running engine, but I don't think that would have been as efficient due to the heavy buildup. The whole process took about 3 hours, but I've gotten pretty good at manifold R+R while troubleshooting this problem.

I will keep the throttle and MAP alternatives in mind, thanks. Next steps are likely a smoke test (I can rent one from a local DIY garage in LA) and maybe try to figure out the logging capabilities of the Foxwell scanner. The light seems to re-appear anywhere between 15 and 60 minutes of driving and after 0-3 re-starts, and I'm not sure if there are specific circumstances that cause it. The logging might help if I could capture the MAP, throttle, and calculated MAF values around the time when the light returns.

mark944turbo

The smoke test revealed a small leak from the PCV valve. I had popped the plastic top off the valve to look at the diaphragm inside, which was in fine condition, but maybe the old plastic housing has changed shape enough that it isn't sealing well anymore. New part is on the way, fingers crossed.

mark944turbo

I think it's solved this time- no CEL after a week of driving post PCV valve/AOS assembly replacement.

KBell

Excellent
Hopefully the CEL is solved.
Still give Rennlist another update after some miles are driven.

F SANE IL

Bringing this back from the dead....

Did these codes ever return? I've got the same exact codes I've been fighting forever now. Have made a parts cannon out of this CS.