gimp2x

the mechanic who filled/topped the fluid put the car in drive but used the e-brake so the tires weren't spinning, do you think this is sufficient to get the trans to a full fluid level? He also filled until it hit 40deg C not 35

I am grasping at straws here i know

Brainz

Several of the vacuum lines (including the one you showed and also the purge valve) are all behind check valves (because boosted engine) and hence won't show a leak under positive pressure smoke test. You have to test the lines individually. It's trickier than it just smoke testing the pre-throttle intake.

gimp2x

we were chasing a code that said "leak between MAF and throttle body" so the thought was air would have to be getting into that under pressure, as a normal condition would be vacuum for that path, and anyways, it yielded nothing, we replaced ALL of the lines leading to the intake path, and now I have not seen the code come back, I'm going to drive around more with PSM on like you suggested and see how she behaves

Brainz

Do you know how many total liters of fluid are in the trans? Once you rule out vacuum leaks, then you might also have to drain/refill the trans to know exactly how much ATF is in there.

My sense is that you've topped it off, so that's not likely the issue if you've got known vacuum leaks. And particularly since you got another 1.5 liters in there -- that's actually quite a bit. A trans that's low by that much may exhibit the slipping under reverse gear upon start-up after sitting overnight. It may also have a slip-bang in drive if going up a steep hill as the transmission will briefly run out of fluid and cause the clutches to slip. What you're describing sounds more like vacuum to me.

Brainz

That's an interesting code given that you've got a vacuum leak in that breather hose. That breather hose connects to the "turbo check valve", which is a large orthogonal, y-shaped valve to the right of the throttle body when facing the engine from the front of the car. I don't know the history of your car, but you may want to check that such valve is working appropriately and/or is installed the right way (I believe you can actually fit it incorrectly). If it's not providing a correct check valve action in the right directions, that could also cause problems including potentially flagging as a "leak between MAF and throttle body" because the down leg of the turbo checkvalve is a breather line that goes into the intake tract on the right side (facing engine from front) just downstream of the MAF.

gimp2x

I recently replaced the following, which I believe you are talking about:

https://www.ecstuning.com/b-genuine-...e/94810721753/

https://www.ecstuning.com/ES1441878/

https://www.ecstuning.com/b-genuine-...e/94811014851/

Brainz

It looks like you've replaced many of the suspect lines already -- that's good.

The "turbo check valve" I was referring to is this one: https://www.ecstuning.com/b-genuine-...e/94810721950/

The turbo check valve connects to the first hose you linked to in your post #21 and also to the new hose that you're planning on replacing per post #11. While I don't think this valve is a frequent failure point, it should be checked for appropriate function and orientation. If you look at it, it's actually possible to remove the elbow fitting and reinstall it the wrong direction. My guess is that your leaking hose (post #11) is likely the problem rather than the check valve, but take a look while you're in there just to rule this one out as it may not otherwise be obvious.

One part I see missing from your list of likely problem areas is the tank "purge valve", which is a frequent source of problems on the Cayennes -- it's this part: https://www.ecstuning.com/b-genuine-...e/94811020203/

The purge valve connects to the fuel evap system. If/when the valve fails (and they seem to fail often), it will fail in the open condition, creating a vacuum leak through the fuel system. But you won't find it on an intake smoke test because it's operationally behind a check valve that's attached to the 94811014751 hose that you've already replaced. Most folks won't realize the purge valve has failed until they experience hard starting issues immediately after refueling, but it's also possible for the valve to leak and not cause hard starting issues.

One way of testing the part whilst on the car is to attach a hose to the intake side of the purge valve and see if you can suck/blow through the line while the engine is off -- you should not be able to. If you can blow/suck air, your valve is bad and should be replaced. As a temporary fix/test, you can also put a small rubber vacuum cap (don't use anything that would cause harm if sucked into the engine) over the intake side spigot on the purge valve and reinstall the hose over the top. This test may throw a EVAP check engine light if you keep it that way for several driving cycles, but it's as useful way of identifying any drivability issues related to the purge valve -- you're essentially just taking the purge valve out of the system temporarily.

Hope that helps. It sounds like you're on the right track.

gimp2x

Yes, I will check the orientation of that valve, but was one of the first I replaced, I also replaced the purge solenoid and the hose that goes with it which runs along the driver's side valve cover to the back of the engine- whole assembly was replaced, the air-oil separator diaphragm was replaced, oil cap o-ring, and throttle body o-ring as well

The only other piece that I believe I have not mentioned is the brake booster hose assembly (955 355 579 51)

as you can see, I'm running out of things to check- any tips on verifying the check-valve/elbow orientation? Just drove around on PSM mode, no check engine lights or codes, even ran the car hard a bit to try and stress the system, no codes...

Brainz

That hose seems to crack and leak too -- but usually you'll get a brake failure warning and/or you'll hear the brake booster pump buzz every time you press the brake pedal.

If this line has a definite leak you need to fix it first: https://www.ecstuning.com/b-genuine-porsche-parts/engine-ventilation-line/94810721552/ That line is famous for the tee cracking/disintegrating at the back of the engine. Many people replace the plastic tee on that line with a brass one as heat at the back of engine seems to do a number on that connection. Also, I incorrectly said above that this line attached to the turbo check valve -- it does not -- sorry for any confusion, but was working from memory.

Regarding the turbo check valve orientation, it should work like this:

Intake vacuum port (on manifold behind throttle body)
^
^
^
X
"Turbo Check Valve" X < < < < PCV Cap port on drivers side (North America) valve cover
X
v
v
v
Drivers side (N.A.) intake pipe post MAF

If you look at the above flow diagram, the "v"s show the permitted direction of flow which is designed to pull a vacuum on the PCV at all times (including boost in the intake manifold). Under engine vacuum, the PCV is sucked directly into the intake; but under boost, the PCV is sucked through the intake pipe. BTW, this is why oil accumulates in the driver's side charge pipe on the Cayenne turbos -- because oil blowby is routed there from the PCV by this valve under boost. Test the valve by blowing into each of the [three] ports. If you can blow opposite the direction of the "v"s in the diagram above the check valve is oriented wrong or the valve has failed. As a practical matter, that means you should only be able to blow through the valve from the PCV leg of the valve as the other legs are designed for suction only.

Hope that helps.

gimp2x

got excited, went to verify the valve, its installed correctly, can only blow on the PCV side

PTEC

Kris Murphy

My 2004 CS was having a odd driveline issue. Under light throttle, the car would start to shudder a bit. I could let off on the gas, and it would go away, or if I gave it more gas it would go away. Seemed to happen more in turns (as I was just applying light gas after hitting the apex). Had it to three mechanics over 2 years trying to figure out what it was. Replaced motor mounts, tires, changed the trans fluid, and it kept happening.

It's not until I read this thread that I realized the problem is gone. The only thing I have done to the car since the last time I had the problem and now, is replacing both valve cover gaskets (they were leaking to the point that I could smell it). Now I have no clue if that is what was causing the problem, and if a mechanic told me that I needed to replace my valve cover gaskets to fix a drive line issue, I would laugh at them, but anything is possible.

BTW, the Pelican writeup on replacing the valve cover gaskets is great, but also optimistic. I think it say 4-5 hours. It took me 12, and I do a ton of wrenching.

Brainz

I battled that shudder for a year. It's in the 2000-2500 rpm range if I recall and is vacuum leak related. I feels like a transmission shudder/vibration issue and is really annoying. You can drive around the problem RPM range with the PSM button, but you still know it's there. Mine was caused by a leaking purge valve. But I didn't find it until I couldn't start the Pig after a refuel and finally had to replace the purge valve.

Another fun one: Years ago, literally one day after I bought my CTT, I noticed it was leaking oil near the front left tire. Well, it turned out it was just too much oil accumulated in the the driver's side boost pipe leaking out the intercooler junction seal and making a mess. Drain the oil; clean it up; crisis averted. Next day I go for a drive and after a good application of boost the Pig goes into some weird transmission limp mode with PRND lit up and generally running like crap -- stumbles at low speed, horrible shift timing on acceleration, OK at steady state, but down on power. Seems like maybe the transmission has crapped out? Nope - I didn't get the boost hose fully reseated into the intercooler the prior day and it just popped off. But rather than a "Low Boost" or similar warning, I got a transmission error. Easy fix, but confusing/scary for the uninitiated. Quirky beasts, but still pretty magic when they run right.

phatz

Mileage of car?
Did you purge the entire system?
Some reading
https://www.sonnax.com/tech_resource...-09d-solutions
https://www.sonnax.com/tech_resource...don-ts-part-ii
https://rennlist.com/forums/cayenne-...l#post14165943

gimp2x

i'll read those threads, we only did the passenger side valve cover gasket, i'm going to do the drivers side gasket and also install the new valve cover breather hose that we mentioned previously, with a metal tee- i'm slowly eliminating what it may be, i drove around in PSM mode and it doesn't do it, so this has me back to vacuum leak and now fluid or valve body issues

The boost gauge can peg out, but I'm not convinced it's as "quick" as it used to be, hard to be scientific about this though without any historical data