Water Ingress

[quattromark]

while driving this morning I could hear water sloshing around, more prominent when braking.

Pulled the NSF carpet up (as far as I could) and there has to be 15-20mm of water in the floor pan - because of the chunky foam backing, the carpet has'nt got wet yet.

Had a look in the scuttle panel - no standing water.

Had a look under the dash, there is no obvious evidence of water marks - and this has happened over the last 48 hours, I did not drive the car yesterday at all - the front has been parked under overhanging trees.

Are there any 'usual suspect' places where water gets in?

[Crasher]

It is usually the plenum chamber drains being blocked.

[quattromark]

So I syphoned around 6 litres of water from the floor pan today - didn't have time to remove the seats and pull the carpets back!

Had a look in the plenum chamber - think I've found the O/S drain, about 25mm in diameter - its under the brake fluid container? - it looks in bad shape, very cracked. Couldn't see another one like it - I'm just presuming there is one on each side?
However, just to the right of this drain is a hole around 40mm in diameter - looks like it should have some form of grommet in it, but it hasn't - should it have something in it??

I take it the drains are replaceable??

[Crasher]

The other is buried and only just accessible from below with the under trays off, crap design… they should be readily accessible. The service sheet glibly states to clean them but it takes too long under the fixed rate.

[quattromark]

so looking at this today - it can't be the drains that are blocked, because there is a 40mm hole next to the drain that I can see - so the water is going to go straight down this hole! - I'm not sure where this hole will dump the water....probably straight into the cabin!!!
I've looked on 7ZAP but cant see if this in fact a missing bung - I'm guessing it is.

It is possible that the problem is the drain by the wiper arms - If I get chance I will remove the trim at the bottom of the screen and see if there is an issue there. It could be that water is getting into the cabin underneath the box that contains the ECU.

[Crasher]

I don’t see as many 4F’s now, it is all later or much earlier Audi’s, I do a lot of classic Audi’s. I remember having a number of 4F’s where the electrics box on the left filled with water, it would cause the charging signal to the battery monitor in the boot to fail.

[dan2485]

Have you checked the evaporator drain for a blockage? as the water drain off for the AC could be going into the car and not out the bottom of the car.

[quattromark]

OK - so it took me most of Sunday, but I have finally figured this out!!!!!

After removing seats and carpet - sponging out ANOTHER 3 litres of water from the passenger side - glovebox out - could NOT see where there could be any ingress of water.

Removed the ECU box (disconnected ECU and associated plugs) cleaned out all of the crud behind it, but it was very obvious there were no leaking seals here.
Put everything back together and emptied 8 litres of water into the plenum chamber - almost immediately water drained out at the bottom of the wheel arch - this proved that the drain was not blocked.

However........

after about 2 minutes water appeared in the rear of the car - specifically rising up through a grommet in the floor pan.

There are 2 (30mm?) grommets which run down the centre of the rear passenger floor - I lifted the forward grommet out and it was almost like a fountain entering the car - I removed the rear grommet and it was just FULL of mud!!

Hoovered the mud out to reveal a drain plug!!! - There are 2 identical grommets on the drivers side - I removed these and they are clear.

So there is a drain channel from the front of the car, all the way down the middle of the passenger (and driver) compartment in a void which ends up in a drain valve by the rear seats!!

I'm wondering if this is to facilitate plenum draining when the car is facing up hill?

On further inspection in the plenum chamber, the tear drop shape drain plug is missing -

If anyone has the part number for the tear shaped drain plug that would be a big help!!