Boost Valve

mchristyuk

Junior Member
Messages
668
Righty gentlemen..

You've probably ready numerous posts from me trying to capture my missing ponies that I'm convinced my 3200 had lost. To recap, it's running perfectly, just felt a bit lacking in "oompf". There has been a number of issues that I've resolved with the forums help (throttle pedal pot, knock sensors & leaking pressure pipes).

Things are much happier now, and certainly if I bury the throttle from standing starts she goes pretty much like I would expect. However when just cruising and putting the throttle in (unless I'm in Sport mode and really gun it so it drops down a cog and goes for the red line) she still feels a bit flat. I hear the turbos spooling up but I just don't seem to get the shove in the back of the seat I'd expect from 400 of Italians (almost) finest.

The symptoms got me thinking about whether a waste gate was stuck open, or not shutting fully. My reasoning being that at high revs and large boost the effect would be less noticeable than at medium boost.

Reading the tech documents suggests that the waste gates are sprung shut, and the boost solenoid opens them when over boost situations arrive.

So I thought if I removed the solenoid pipe to the waste gates that they won't get opened when needed.. obviously I won't want to run the car like this for long, but it would do as a quick test to see if there was any difference. If there was no difference at all, then surely a waste gate must be stuck open? If it starts to pull like a champion then the boost valve must be at fault...

So been out for a quick spin and it appears my limp mid range has indeed gone and the engine feels much stronger. So I believe my boost valve (pierburg valve) is at fault?

I've read the threads on here about them and I have cleaned and checked the connectors and they are clean and good. I've also applied volts to it and heard it click so as far as I can tell it's "working" as much as my basic tools can diagnose.

So to my questions..

1) Could the valve be reading incorrectly and therefore venting the waste gates early?
2) Could there be anything that makes the valve think the pressure is too high? (I can't see how as it's a pretty simple closed loop system..)
3) Is there an alternative part? I've read that they are no longer available.. but that most turbo pierburg valves are very similar and the chances are another one will fit? Certainly there are some VW ones that look very similar...

Cheers!

Mark
 

Contigo

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I assume yours is a wrong un? Ie auto.

If so then it sounds like it could be valve related.

I changed mine because it was throwing over boost faults. I have a spare one or should I say potentially faulty one I could send you to try out on yours.... Have you cleaned your map sensors? A gold dosing of contact cleaner on both sensors has eradicated limp mode on mine and resulted in smoother running.

Let me know if you want me to send you the Pierburg valve
 

mchristyuk

Junior Member
Messages
668
Hi Phil,

MAP Sensors? I was aware of only the one MAP sensor?..

Mine is an Auto yes.. I'm not getting any errors anywhere..

Cheers

Mark
 

hodroyd

Member
Messages
14,150
Are all your turbo related hoses in good nick, there is one in particular that goes around the back of the engine area that can get crushed, or split, common problem..!!
 

Contigo

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18,376
Yes Mark there are two. One on the bulk head and one on the off side wing in the fuse relay panel.
 

Contigo

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18,376
You mention that it feels flat in non sport mode. I was under the impression that it changed gear at around 4500 rpm but in SPORT mode changed much higher up the rev range. I will dig the actual data out of the workshop manual when I get back home.
 

mchristyuk

Junior Member
Messages
668
Hi Robert,

I've checked the hoses as best I can without taking everything completely out and examining on a workbench. They appear to all be ok and nothing is caught up anywhere. As I disconnected the boost sensor forcing 100% boost all the time and the car felt good, I'm presuming that shows the pipes from turbo to intake are good?

IF I had a leak on the sensor/MAP side would that not lead to an over boost situation as the sensors wouldn't be seeing the increase in manifold pressure as the throttle is opened, and therefore wouldn't trigger the waste gates?

Just thinking out loud!

Cheers

Mark
 

mchristyuk

Junior Member
Messages
668
Hi Phil,

I was only aware of the one on the bulk head. I'll take a look in the relay panel and check out the other one.

Just thinking about this.. if a MAP sensor was faulty I would expect a CEL, and from my reading on MAP sensors some form of rough running engine. It's not rough and idles fine, etc.. no missing or pinking..

As I mentioned to Robert, IF my pipework was leaking to the MAP sensor I would expect (in my logic) that it would lead to an over boost situation NOT an under boost?

You are right about the Sport mode. In normal it changes much earlier. However even in Sport mode I don't get the punch I would expect until about 4.5k rpm. This is why I thought my waste gates were stuck open as it would be noticeable more at low/mid RPM than at high RPM (again in the logic in my head anyway!!). That's why I tried disconnecting the boost sensor to force the waste gates shut.. and bingo, things felt much better.

Soo... I'm sure I have an under boost situation and my test shows there's probably not a leak between turbo and engine intake. If there was a leak on the boost control side I would expect over boost (Though I could be wrong on that!)?

You say a good dose of contact cleaner on the MAP sensors.. I'm guessing you just mean on the electrical connectors?? OR do you mean inside the sensor down the pressure nipple too??

Cheers

Mark

Something is telling the boost valve to open too early.. or it's just doing itself. So either i have a faulty MAP sensor(s) or a faulty Pierburg
 

Contigo

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All over them mate. And as you say a MAP sensor will usually throw a CEL and Lou running.
As I said feel free to try my old one if you like. Let me know your address and will pop it in the post for you.
 

mchristyuk

Junior Member
Messages
668
Hi Phil,

Ok.. I disconnected the Pierburg again and this time it didn't seem to bring the benefits I felt last night. Hmmmm..

Something very odd is going on and I'm struggling to put my finger on it.

I spent some time taking a number of pipes off the air intake system to look for splits, leaks, etc.. didn't find anything massively amiss. And on taking it out I'm still suffering the same symptoms. However I did notice something...

1) If I'm at low revs and virtually no throttle, banging the pedal down in Sport mode she really takes off and goes for it. I've tried timing the 0 to 60 and it seems pretty close to what you'd expect.

2) if I'm cruising along at say 30, get to a 60 limit and pin the throttle it just seems to "gather speed". Just doesn't feel like the rocket I'd expect.. almost feels as if it it takes as long to get from 30 to 60 as it does 0 to 60.

I'm wondering whether the throttle butterfly is sticking?!.. Could it be that going from closed to wide open managed to get it through the "sticky spot"... but going from 25% throttle doesn't give it the "run up" it needs??.. sounds mad.. and I would have thought it would throw a CEL if the butterfly was sticking?..

I will get to the bottom of this :)

Cheers

Mark
 

mchristyuk

Junior Member
Messages
668
Ok.. just popped off the inlet pipework and had a feel of the throttle butterfly and it was smooth and free.

However I did notice a dark oily film on the nearside side of the throttle body intake pipework. The sinking feeling in me suggests that the nearside turbo has gone "phut".. and hence the lack of oompf?... The offside set of pipework is bone dry..

Cheers

Mark
 

alfatwo

Member
Messages
5,517
But you're in a higher/different gear by then Mark It's bound to feel a little slower..

If your in third gear at 60 in a manual 3200 it does take a few seconds to get going like you say then all **** lets loose
you have to be focusing!

The old 3200's are fairly impressive for such a heavy car...

Dave
 

mchristyuk

Junior Member
Messages
668
Hi Dave,

Yes I understand that, but it never seems to get going.. all **** certainly does not let loose. I'm convinced my previous 3200 had much more beans to it than my current one. It's not slow.. it's just not 400hp..

Looking at the oily film maybe that is the smoking gun and I'm a "turbo down"..

Cheers

Mark
 

Almichie

Junior Member
Messages
799
I wonder if the pedal isn't set up, or hasn't been adjusted in years. Have you tried a reset?
 

Contigo

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Good shout Al. Get a multimeter on it Mark and measure the output at the yellow or white wires with the pedal fully depressed. Should be over 3V.
 

mchristyuk

Junior Member
Messages
668
Hi Phil/Al,

The pedal was wrong when I first got the car which meant it didn't always red line in sport mode. That's been rectified!

The Kayser valve has been mentioned to me regarding my lift off whistling (my old 3200 did not make this noise!). I'm wondering if it's loosing boost through that? Seeing as earlier cars didn't have one at all surely I could just bypass it for a test?

Edit.. Having thought about it I can't see how it would effect turbo power?! And those that fail whistle on boost not off boost.

I'm thinking my off boost whistling is related here but can't for the life of me think what it is.

It doesn't do it when revving the engine. Only when the dump valves operate under load and lasts for about 1 second longer than the dump valve 'pssst'.

Perhaps I have a leaky dump valve that's constantly open a little?!

Cheers

Mark
 

Almichie

Junior Member
Messages
799
It could indeed be a sticky valve; my mini dump valve stuck open and lost a lot if pressure. These recirculate back into the inlet but work in the same way. Be worth taking them out and testing them. I plan to swap mine out for faster shutting versions at some point
 

Contigo

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Yep there's a good mod for the Audi RS4 N75 Diverter Valves so maybe there is a better more robust part for our Recirc valves?
 

mchristyuk

Junior Member
Messages
668
Righty.. I removed the drivers side valve for a looksy and it all appeared fine and dandy. It's incredibly simple and I can't see what much could go wrong with it. I guess the spring could have weakened with age. Without a new one to compare to it's difficult to say. However if it was leaking I would expect it to "whistle" under boost.. and I can't hear any odd whistling under boost.

But I do have this weird whistle when coming off boost which I swear is connected as my old 3200 didn't do it, and it lasts too long for a dump valve.. plus I hear the valves "Pssst"ing as they should. I recorded a little video of it today.. What is this sound?!

http://youtu.be/TdyczZVWSWE

Cheers

Mark