What now for the AEB?

Lee Goodall

Lee Goodall

Registered User
Joined
Oct 22, 2007
Messages
2,273
Reaction score
4
Points
38
Location
UK - Midlands
After trying to iron out issues with boost control a big problem has come to light!!!

Pressure testing my boost system has indicated that I have an issue with the cylinder head/valves/valve seals.

I am getting a large amount of boost leaking back through the cylinder head and exiting through/around the oil filler cap!!

I presume this is down to one or more faulty valve seals unless anyone can tell me differently?

What should I do?
 
i think its possible for this to happen thru the breather system?

Might indicate a faulty 1 way valve or something. The inlet is connected to the breather system and there is a 1 way valve thats supposed to close under boost pressure. Have you plugged/disconnected the PCV line before pressurising the inlet?

Valve sealing issues wouldnt allow boost pressure into the rocker cover, and would show up in a compression test as low compression on that cylinder.
 
aragorn said:
Valve sealing issues wouldnt allow boost pressure into the rocker cover, and would show up in a compression test as low compression on that cylinder.
Click to expand...

think he means "valve seal" as in the noun
rather than "valve sealing" the verb.

knackered valve seals and guides would allow boost into the rocker cover....but it would also show up in your exhaust as huge plumes of smoke
 
Yeah thankfully no smoke so will hopefully turn out to be an easier fix than I first thought. There's no obvious poor running (other than the boost issue) so I'm guessing there's no compression issue.
 
aye it sounds like your feeding pressure thru the PCV valve on the turbo intake pipe into the breather system. The 1 way on the breathers T-Piece stops the boost normally getting thru into the crankcase under boost from the inlet, but you've kinda bypassed that by creating boost pressure in the TIP. :p
 
Yeah.. needs blocking off at the TIP for boost testing!!. Doh!!

So no pressure should come through the valve (from breather to TIP) under boost then obviously?
 
I thought the PCV vented the cylinder block?.. How does the pressure from the boost test get into the head? I'm confused now.
 
you need to block the connection on the y pipe for the pcv , i air is coming through the pcv then 1 or more of the 1 way valves in the spider assy will be bad , you can get the whole spider with the valves and may aswell do the fhose delete while installing
 
The boost tester connects to the TIP which is non pressureised anyway, it is however connected to the PCV system via the pancake valve, so as such when you send pressure through it it feeds direct into the sump, seeps past the rings sometimes. But as Lee has already found the air in the PCV system makes the oil bubble and can be heard through the oil cap .

The pancake needs to be blocked off so when pressuring through theTIP the air goes through the turbo and then into the pipework inc DV though the FMIC and into the the throttle body. There will be a small seepage past the throttle butterfly but nothing to write home about.
 
andyb: its a 1.8T not an S4, but the principle is the same.

Lee: the pressure gets fed to the sump, sump is connected to the head by a number of oil drains which the air simply flows thru and into the rocker cover.

The Idea is that the crankcase should be under vacuum at all times when the motor is running. In an NA engine you simply connect the inlet manifold to the breather and that does the job, and this connection is still there on an AEB for when its not making any boost. However when it does make boost the inlet is no longer in vacuum, so on an AEB there is a small 1 way valve (sits on the end of the T piece thats connected between the Z pipe and the metal hardline that runs to the pancake valve) which blocks the inlet vacuum supply once it becomes pressurised, and instead uses the pancake valve so the gasses are vented to the turbo inlet pipe, as thats the only place in the system there is still negative pressure.
 
Ok that explains it then.. the pressure finds a route to the head from the sump via the oil pipes etc if the PCV isn't blocked off.

When the system is pressurised 'properly' with the PCV blocked how long should it hold the pressure for at 17 - 18 PSI?
 
quite a while? i'd expect it to start dropping pretty quickly if there was a leak, accomanied by some hissing...

Otherwise its just whatever leaks past the rings?
 
It held for about 40 - 50 seconds but decreased throughout.. this sound ok? No hissing or obvious leaks anywhere.
 
i'd have thaught it would have held a little longer? Try it with the throttle body open? as perhaps its just slowly leaking past there into the cylinders? Once the cylinders are full it should hold for much longer i'd think?
 
Hmmm yeah to be honest I thought it'd hold for longer but def worth I try with the TB open. As you said maybe the throttle plate is holding some pressure.. Hopefully get another chance to test it soon.
 
A pic from last night.. Trying to get the TIP back on the turbo in the dark after I blew it off while testing!! Had to take the headlight out to get to the jubilee clip properly.

Nearly popped my eardrum when it blew off!

SP_A0154.jpg
 
To be honest mate I have had a manic weekend and not had time to test it with the TB open yet. I was hoping somebody would have some previous results though just as a guide.
 
You must log in or register to reply here.

Similar threads

L
now what ?
Replies
7
Views
963
aragorn
A
ALPINE
NOW WHAT!!??
Replies
39
Views
2K
ALPINE
ALPINE
Lee Goodall
What now?..
Replies
11
Views
1K
Lee Goodall
Lee Goodall
H
Facelift Grill Done!, now for the lights :)
Replies
8
Views
1K
H2o-uk
H
Oranoco
What boost pressure on chipped AEB?
Replies
5
Views
1K
AUDI TURBO
AUDI TURBO
Top
Back