Boost issues.

[Jas11n]

Cheers Bo, maddening aren't they

Have I got this right in my head?
The lower port of the wastegate is presented with vacuum from the maf hose to keep the wastegate closed beyond spring pressure. When appropriate, the WGFV switches the feed to the pressurised air from the port on the coldside of the turbo to force open the wastegate??

[AndyP]

Replaced front knock sensor with a new one, still no boost above 0.4bar.
In fact, she'll not boost beyond 0.2bar most of the time.

I'm at a loss now. I've changed everything possible bar taking the engine out and giving it a good kicking

Is there any way I can "briefly" force it to boost to rule out maybe damaged hotside blades of the wheel . I don't fancy taking the turbo off just yet if there's an easier way first.

Unplug the WGFV and put a 1.9bar spring in the wastegate, that'll force it to boost I have one you can borrow if you want, at your own risk obviously!

[Jas11n]

Unplug the WGFV and put a 1.9bar spring in the wastegate, that'll force it to boost I have one you can borrow if you want, at your own risk obviously!

That'll mean butchering the wastegate cap wouldn't it Andy?
I'm not wanting to leave it like this obviously, just wanting to confirm the the turbo itself isn't dead.
I thought, unhook the hose from the WGFV that goes to the coldside and bung it. Hook a hose up direct from the maf hose to the lower port of the wastegate.
Assuming the turbo ain't tit's up, I should get more than 0.4bar of boost, although it'll be boosting full on before WOT

Sound right?

[AndyP]

The uprated spring drops straight in, no mods req'd. It's the same size as the std spring, just a lot stronger. I have a 1.2bar one too if your not feeling brave!

[S2central.net]

You can try a couple of bodges here...

1 - The big 1.9bar spring and disconnect WGFV - this will provide max boost of 0.9bar - safe to the redline on K24

2 - Keep factory spring and bodge the WGFV to be active all the time (apply 12V across it) - forces the turbo to keep boosting until EXHAUST manifold pressure cracks the WGFV open... Not at all elegant and you'd need to keep a close eye on boost levels to run like this - actually the ECU might throw toys out of the pram before you get into any dangerous territory. Never BTDT on this one.

[S2central.net]

Only other thing I am thinking about here is that your WG might actually be stuck open....

When the WG cap is on and you applied vacuum - sucking the valve upwards - did you hear a nice 'thunk' as the WG spring closed the valve when you removed vacuum ?

Does the valve move nice and freely when you have the WG cap off ?

[s2_bo]

Good call Paul, maybe that's it......

[Jas11n]

Only other thing I am thinking about here is that your WG might actually be stuck open....

When the WG cap is on and you applied vacuum - sucking the valve upwards - did you hear a nice 'thunk' as the WG spring closed the valve when you removed vacuum ?

Does the valve move nice and freely when you have the WG cap off ?

The car was down at my local specialists when the wastegate diaphram was tested. They had a handheld vacuum thing (mitivac?) and said it held it's vacuum.
They didn't however comment on the being able to tell if the valve was ok.
I'll whip the cap off tomorrow morning and see if it operates smoothly.

Thanks for the pointers, this is new territory for me having never had anything remotely like this in the 5.5 years I've had her.
I'll nail it eventually

Thanks to Andy for the loan of the 1.9bar spring too

[Jas11n]

One thing about the WGFV has puzzled me though.
The original valve was click-clicking away fine when running output test mode in vag-com.
If you held your hand on it and revved the engine, you could feel it clicking away like mad.

The new WGFV clicks away just the same when in output test mode, but does not click when revving the engine as above.

Why is that?

[Jas11n]

Bump.
Need to be able to cross this anomaly off the list.
Which is correct? If I rev the engine, should I be able to feel the valve clicking or not at all?

[FITZY]

When I give mine a quick sharp flick of the throttle pulley when stationary, mine clicks away like a good un'. Does have to be quite a 'hard' rev though if you get what I mean.
HTH

[Jas11n]

Thanks Fitzy

Hmmm there's a bit of a rabbit away here me thinks

[S2central.net]

Never actually felt one for clicking with a rev at idle - suppose it should right enough...

Rather than just hear it click - would be better to remove the hose from WGFV that goes to lower chamber of WG - then at idle when your testing the WGFV you should feel vacuum on the exposed end of hose when the WGFV is active... That proves its actually working.

[Jas11n]

Righto, thanks for that.
Will be out in a bit to go at it a bit more

[Jas11n]

A couple of lessons learnt on this one.

1/ NEVER buy cheap sh*t .
2/ NEVER use a garage you don't 100% trust .

is it worth having a look at the cats? i know you replaced them recently but wondered if they might have broken down?

Gav?? you my friend I owe copious amounts of beer to.

I'd ruled out "everything" electrical that the ECU uses to regulate boost. The car has been getting less and less boost, as mentioned above it was really struggling to get 0.2bar yesterday. Today it was barely registering any boost at all. Through the invaluable advice above (thanks again guys) I'd set it up to "force it" to boost beyond mechanical spring pressure and she still didn't want to play ball.
That said to me either it was a dead turbo or a wastegate problem.
Fug it, time to get it down to my trusted local specialists (Volksparts of Durham LTD) and bash heads with the lads.
The wastegate cap came off and the valve was moving freely, I again bunged the hoses up and retested to make 100% sure.
All that checked, I dropped the car down resigned to the fact the turbo was dead. Pulled the car out of their garage and then remembered I'd forgotten to put the undertray back on (DOH)
Back up on the ramps and one of the guys (Stuart) started bashing his fist against the exhaust. I banged both cats and they sounded like they were full of marbles.
Off came the cats and we were shocked at WTF came out of them .

I'd paid another so called VW/Audi specialist on Tuesday to take the cats off to check them. B**tards have charged me for something they haven't done

How the car ran at all is beyond me. I'd thought about this time and time again, but always came to the conclusion that the car would hardly run with a blocked exhaust. It did, and just goes to show how the lack of backpressure is SO important to a turbocharged motor. It's been nigh on the same as driving around with two bloody potatoes stuck up the tailpipes.

We proceeded to bash the rest of the crap out of them and both had this big ball of melted rubbish in the middle. Unbelievable.
Refitted the cats and jesus it's good to see she has her mojo back. Boosting like hell and fast as fug again WHOO HOO

The guys at Volksparts would not charge me a penny either Fantastic set of lads.

NEVER buy cheap crap and never take your prized S2 to a garage you don't 1000% trust.