Engine Noise - Vacuum Leak and/or Water Pump?

[iamtheari]

My 2004 CTT definitely has a vacuum leak. I get codes 2187 (about once or twice a week) and 2189 (recently started, comes on only with 2187). I haven't found the leak yet. I am hoping it's something easy. And I am hoping someone can help me track it down without just replacing everything between the MAF and the intake valves. I don't have that kind of time.

I made some videos to show the sound that the engine makes. I feel like this is probably related to the vacuum leak. Especially note the sound when I shut off the engine. It's like it takes one last breath of air after the crankshaft stops rotating.

I also mention the water pump just because it's a common point of failure on these cars and I don't want to rule it out just because the coolant level and engine running temperatures have remained stable since I replaced the leaky expansion tank and flushed the coolant about a year ago.

Here are the videos:

Front grill - YouTube - Front grill. When I move the camera down from the badge to the grill, the offending sound fades in.

Engine - YouTube - Engine, aimed at MAF. The sound is steady from this angle.

Shutdown - YouTube - Shutdown. I turned off the ignition right after the video started recording, and you can hear how the suction sound continues shortly after the engine stops.

Any clues are appreciated. I'd like to fix the leaks soon so I will have a reliable car through the winter rather than having to work on it. (Winter project is rebuilding the 964's engine, not monkeying with the Pig. ) Thanks!

[Andrea Bichael]

I think engine noise mainly due to vacuum leak and valve problem. So, one should check the car parts to know if there is any kind or not. You should replace your damaged valve as soon as possible. You have to repair your vacuum tube for good result.

[dzlndan]

On the vacuum leak- I know it is real tight in the engine bay but did you try spraying some carb cleaner around where it sounds like the leak is coming from. The idle will change dramatically if the carb cleaner gets near vacuum leak, this would help you to pin point that problem. Usually when a vacuum leak is that loud it is something that can be found from the exterior of the engine. Just my 2 cents

[iamtheari]

I tried spraying around with carb cleaner but it was dark and chilly out so I probably could have done a more thorough job. I did not find any changes in the idle while spraying around the throttle body area. I'll try again when time allows. I should note that the idle does increase dramatically when I open the oil fill cover, in case that helps diagnose where the leak(s) is/are. I agree that this should be easy to find given how loud it is. Thanks for the responses so far.

[island911]

Air pump? ...Is the frequency of the leak synchronized to the engine revs? --if not then air pump suspect

Listening to your engine video I would agree that you have a vacuum leak for one of the cylinders. But that last, shutdown video...

[iamtheari]

I did recently replace the vacuum lines for the brake booster. Both the long one behind the firewall and the three-ended one that connects directly to the vacuum pump. I honestly do not recall if this sound started before or after that. I do not think it is related as those vacuum lines seem to have nothing to do with the engine and the engine is complaining about running lean.

Earlier, I experienced very very occasional CELs when filling with gas. Online reading led to the conclusion that the most likely cause was the vacuum purge valve failing. I replaced that five months and about 7,500 miles ago. There was definitely a break in between then and when the engine started throwing the current CEL codes.

What I get is occasional 2187 and, less often and more recently, 2189 CEL codes. These are left and right bank too lean warnings. This tells me it is a vacuum leak allowing unmetered air into the combustion chambers and that it is not localized to one cylinder, which tells me it's before the intake manifold. But I could be entirely wrong about that.

Tell me about the two air pumps that block removal of the plastic ignition wire covers. Are they potential culprits here? Is there another air pump I am not aware of? I will check the revs vs. leak next chance I get and agree that it would be an important piece of information in diagnosing the problem.

The sound at shutdown seems to me like it is a relatively slow leak of remaining vacuum from the same place as when the engine is running, once the source of vacuum is removed. Is it telling you something different?

[iamtheari]

It definitely does change with RPM. Mostly it goes away and/or is drowned out at more open throttle settings. But in the narrow RPM band when you can hear it, the noise basically becomes a smoother suction sound as the pulses get closer together.

[iamtheari]

I started the car this morning to warm it up for my wife and, while I waited, popped the hood. It's really hard to isolate the source of the noise but it is strongest near the throttle body. Loosening the oil fill cap causes the air-oil separator to wheeze a bit and RPM to change. Removing the vacuum line from the front side of the air-oil separator causes the RPM to change drastically of course.

So, what's my next step? I don't want to blindly start replacing parts here if I can avoid it.

[iamtheari]

For posterity: I had a dealership look at this one. What happened was the vacuum line "nest" had found its way into contact with the water pump, which wore a hole into one of the lines. Replacing the "nest" of vacuum lines and ensuring they were secured in the proper positions fixed the problem. No noise, no CEL.

[Brainz]

Glad to hear you found the leak -- the vacuum lines on the Cayenne are very complex, and can cause weird running issues when there are leaks.

Interestingly, my purge lines under the throttle body also found their way into the water pump pulley and got chewed up. While mine didn't get damaged to the point of noticeably leaking or throwing codes, it was pretty close to failure.

I spent today chasing down a vacuum leak that appears to have been the brake booster connection at the back of the intake manifold. I must not have completely seated it when I replaced the coolant pipes last month. Appears to be cured now, but interesting that it didnt throw a code or affect braking -- maybe because of the aux vacuum pump for the brakes on the CTTs. But it sure made the car run unevenly and shift poorly.

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[iamtheari]

I didn't realize there was an engine vacuum line to the brakes at all. I thought they just ran off the auxiliary pump. Mine had a cracked fitting that I fixed last summer. The brakes got a code but never leaked badly enough to affect braking performance noticeably.

[Brainz]

The vacuum brake line on the turbo is interesting in that it has 3 ends: One is the snap on fitting under the plastic intake Y in front of the throttle near the rubber T vacuum fitting that got chewed up on your car and mine. One is a snap on fitting to the back passenger (RHS) side of the intake manifold that was loose on my car and caused driveability issues. The third leg goes merges with the electric booster line that goes to the brake booster.

What I think is interesting is that the 3-way line appears to have a Venturi pump in it which enables the line to supply vacuum to the booster under both vacuum/idle conditions as well as under boost. No idea how well it works but that appears to be the design intent.


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[iamtheari]

Yeah, the three-headed hydra vacuum brake line threw me for a loop since it is not depicted in the parts diagram, which just shows the non-turbo version. What had happened with mine was that the long vacuum line behind the firewall had split at the fitting to the three-ended line, so I replaced both the long one and the three-ended one. I didn't spend a lot of time figuring out where all three ends went, though. One went to the electric vacuum pump, one went to the brake booster at the master cylinder, and the other went somewhere else that I assumed was related to the turbocharging machinery. If memory serves, it pulls a vacuum through that line toward the vacuum pump. But maybe it was the other way around and pulled a vacuum toward the intake manifold so the electric vacuum pump only has to work when the throttle is open?

All I know is that replacing both lines fixed the brake booster warning...and cost me a watch since one half of a link decided to fall into the depths behind the firewall beyond where I could fish it out with any tool on hand. Typical Porsche--it demands sacrificial blood, tools, and even jewelry every so often.

[Brainz]

Yep. See my updated post above for the 3 line ends.


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[Brainz]

Also, the vacuum line diagram sticker on the top of the radiator bulkhead was helpful, albeit still difficult, in figuring this out.


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