Boost leak. What to check?

[danW]

Hi all, hoping someone can help with pin pointing a boost leak.

I’ve had my mk5 for a few months now. At first it went like a rocket right through the rev range but recently it’s lost some low down power and whistles a lot, lower down in the rev range. I bought it with the pcv and dv done recently and had the cam follower done. Since owning I’ve replaced the dv rev d for a rev g and today replace d the pcv. Still got boost issues. Any ideas what to check next?

Can anyone help with the process of elimination?? What’s next? Boost pipes? Any known failures? I’ve got no engine lights or codes throwing up from the reader.

Any advice would be great.

Thanks all
Dan

[JoshB]

Mine was the PCV pipes themselves, if they creak then they’re knackered. Should be silent and flexible.
Whilst it made an instant improvement, it wasn’t until I replaced the brake booster hose that I was back to 100%.
Also check the pipe at the back of the engine (under the turbo inlet hose inline with oil filler cap), can’t remember it’s name but they’re prone to cracking.
There’s the obvious stuff like intercooler pipes, if oils dripping from the joins then the seals are leaking.

[LC5F]

The basics have already been covered-
PCV hoses do like to get crunchy with age - if you have replaced the PCV itself I would be checking the state of the disturbed pipework.
The clips in the boost pipe alloy bayonet connections tend to loosen due to constant expansion, making the joint move.

The more random locations to check are:
Rocker cover gasket - the rubber hardens with age and shrinks/splits, tell tale is oil on you plugs
Breather pipe at back of rocker cover to turbo intake - some have perished, or as the can be tricky to re-install have been bodged back into position.
On a K03 turbo, there is an o-ring in the outlet silencer that can fail - it is PITA to locate both its PN and to install.

[pudding]

I would start with the Boost pipe O rings and go from there. There's 3 of them, one at the turbo end, one at the connection under the crank pulley and one at the intercooler end.

They are a strange double lip seal and tend to wear out, especially the middle one from all the engine movement.

[danW]

Thank you guys, really appreciate the support. Hopefully it’s the cheapest first! Starting with the o-rings I think. I noticed oil on the metal pipe leading to the drivers side of the intercooler. Hopefully a new seal from the o-ring will sort it.

Cheers
Dan

[ROH ECHT]

As already mentioned, check the boost plumbing seals. But other ways it can lose boost is if any check valves have failed for the systems which are attached to the intake manifold. Being: EVAP/N80, PCV (not likely since you've done it), Brake Booster. You simply disconnect each tube/hose and try blowing into them. Sealed means no boost lost. As they utilize the vacuum to operate on. But they all have check valves for when in boost. So, if a check valve is shot and and you are able to blow through them...you may want to run some smoke through them to locate any leaks in their tubing.

If you reach the point of confidently determining it has no leaks, you will need to diagnose the waste-gate and actuator function, as well as the N75.

Once this is done and appears OK, it may be the turbo itself. Hopefully not.

There are four seals....three are the same and one other small one up at the turbo outlet.

[mjmallia]

I noticed at the weekend a vacuum leak at idle on the boost gauge, on checking the usual I decided to check the oil cap and the complete neck extension came off the cam cover with cap attached  heat cycles must have taken its toll on the joint. The cap is now directly on the cover, so looks a bit odd with the engine cover on  but I can live with it at the moment...........worth a check

[LC5F]

There are four seals....three are the same and one other small one up at the turbo outlet.

Excellent image - the green one at the turbo outlet is the one I was wittering about! - apparently K04's don't have this one

[pudding]

There are four seals....three are the same and one other small one up at the turbo outlet.

Excellent image - the green one at the turbo outlet is the one I was wittering about! - apparently K04's don't have this one

They most certainly do.  S3/6R intercooler upgrade does away with number 6 at both ends of the intercooler.

As I myself have been wittering on about, it's number 6 on the discharge pipe (part 9) that wears the most (because of all the engine rock), which also wears out the bore of said pipe as well, which no amount of new O rings will fix.  A new pipe is the only way to fix that particular problem.