Engine bay noise - identified
 

A little while ago I posted about a strange "farting" noise from the engine bay. Oddly I can't find that post/thread now. :Confused:
I recall various suggestions to investigate, related to vacuum piping.

Anyway, while sorting out the F125 P/N starting inhibitor issue I have, I've been starting the car a a lot while cold and noticed it was getting a lot louder.
Today, with help and the bonnet up, we quickly identified the source.

It's the PCV valve! Makes a wonderful trumping sound, though just a little hand pressure stops it.

A problem identified, is a problem managed and to be solved later. +++

Might be a damaged or poorly-seated diaphragm, who knows. I have a spare one anyway so will look at it another time. :cool:

I've replaced mine a few times. I would've described it as more like a honking goose noise. But maybe that's what your farts sound like? :ROFL:

I've fitted a couple of genuine PCVs in the past, which didn't seem to last long. Currently I have a Meyle PCV fitted which has probably lasted the longest.

I remember the thread in question, and thought it sounded much like the PCV fault we had on our C5 A6 3.0 petrol back in the day....

I just replaced ours with a new one - wasn't horrifically expensive

That's what it sounds like now. :D
They are very simple devices, so I'll just take it apart and see what I find.

I have a spare from when I swapped it ages ago, might even have been on the old S8. (Edit: it wasn't. Just soon after getting the FL one)
After swapping I took the original apart and found that all it needed was a good clean and the diaphragm reseating. So that can be swapped back in if necessary.

The only "tricks" to getting them off (after removing the central engine cover) that I recall are:
1. Get a pair of Click-R pliers if the original clamps (Click-R) are still in use.
2. Rotate the clamps (one of mine is a Jubilee IIRC) so that they are easily accessible next time.

Interesting. Took the PCV off today, checked and cleaned it (all looked OK) and put it back.
The lower pipe connection was pretty loose so I presumed that was leaking and making the noise. I made sure it was really secure.
Wrong! Still honking. :mad:

Took it off and fitted my old one. No honking. +++
It actually has a small slit right at the edge of the diaphragm, but when I tested it (sucking and blowing!) it seemed airtight, so I think the case is holding it adequately.

Further investigating the "honker" I took it totally apart and found a 5th component! I had thought there were just 4 (upper and lower case, spring and diaphragm).
Behind (above when fitted) the main diaphragm is a small (15mm or so) diaphragm/valve made of orange silicone rubber.
If you peer in through the small vent at the top of the unit you should see a tiny lump, 2mm or so, of that rubber. It's a little retaining plug moulded into it that pushes through a small hole in the case.
Except on my "honker" you can't see it, because it's missing. Must have broken off, disappeared into the engine and been cremated!
So that little valve can move around, not as designed, presumably allowing the noise to be generated. What problems if any that causes I've no idea.
See attached photo. You can see a little lump inside the vent, but that ISN'T the normal lump of orange silicone rubber, it's a tiny bit of the stalk and a lump of Evo-Stik glue! :tuttut:

So I currently have one PCV with a dodgy main diaphragm (fitted) and another with a faulty secondary diaphragm (being glued into place for testing).
I could easily make one working unit from them, but I'll wait until the one I've ordered arrives and see what the components are like.
Hopefully I'll then mix and match to make one excellent unit and one serviceable spare and bin the rest. :cool:

Final comment (for now) is that having learned more about real/fake parts I can see that the "honker" isn't a genuine Audi part. I thought it was when I bought it. :o

IIRC, when mine first started honking, just changing the position of it (pushing against it or holding with a cable tie) would sometimes make it stop. After replacing it, I performed an autopsy on the old one and discovered a tear in the diaphragm. When the second one failed (which was supposed to be a genuine one ... though perhaps it wasn't) I just binned it and replaced it with a Meyle part. I only really took the first one apart for my own curiosity, just to see what was inside.

Have you figured out an easy way to get them open (without damaging the clips)? I remember it took a bit of patience and 3 or 4 screwdrivers, trying to get all the damn clips released at the same time.

I just work around the clips popping them open with a screwdriver, it's very easy, especially if you make sure it's nice and warm first. :Confused:

There are 6 clips in total and 4 of them have slots in the lower casing to push a flat screwdriver through and release. The two opposite each other at the "sides" (big pipe being one "end") are free to access from below anyway.
I usually start next to the pipe, free one each side, then the middle 2 and finally the back 2. Never had an issue or caused any damage.

I must've been doing something wrong when I took mine apart. I just remember how, while I was releasing one clip, another would snap shut. I'll have a closer look the next time I change one. Perhaps I was just being a little impatient with it.

Not a happy bunny. :mad:
The PCV I ordered just arrived and it has two faults:
1. The case top is split around one of the clips, probably broken by careless assembly.
2. The smaller diaphragm is totally missing!

That's annoying. Is that a genuine part?

Presumably the seller will replace it?