Oh Oh, Cant be good!!

[BigDaz]

Well I discovered why I am getting so good MPG last night.
Vagcom threw up a fault code - something to do with boost pressure devation will post more details when i get the log file.
Rolling road showed that the turbos are boosting then immediatly shutting down, not holding the boost.
Max BHP was only 222.7
So basically I have a V6 engine with a couple of turbos for show atm LOL
At least they should be in good nick, they arn't doing anything
Anyone had anything similar?
btw new MAf & 710N's last week, so not that.

Daz

[ChipHazzard]

daz check the TBB and F hose as these are common culprits especially the TBB

[maxxximus]

Who replaced the 710ns - could be poor join, cracked hoses etc . Get it pressure tested.

[BigDaz]

LOL, 710N's were fitted by me, any suspect pipes were also replaced so thats not the problem.
Prevoius owner said it had been in twice in last year to get pipe onto offside turbo fitted back onto turbo as it had popped off, can you jubilee clip these on?
I will ahve to get the tools out & check the F pipe (prob will get rid of it altogether) and TBB (where is this located? )

Daz

[ChipHazzard]

the TBB is located to the right of the F hose and is the Y shaped hose in the middle of the front of the engine.

If your talking about the clips for the small vaccum hoses the just use cable ties on them this is what I've done after i replaced my DV's etc after suffering a similar problem.
I'd also suggest getting it along to MRC for a health check if your still having problems

[S4TAN]

BigDaz - your TBB (Throttle Body Boot) is the large-bore Y-shaped rubber hose that goes into your throttle body - right smack in the centre at the front of the engine in between your DVs - it has a sensor attached to the top. (all underneath the "Audi V6 biturbo" engine cover) - the OEM one is a well-known weak spot on these cars. The F-hose is a bit of a bastard to get to and is also a well-known weak spot - to delete it altogether I think you need a catch-can - maybe better to just get a Samco f-hose as i did (same for the TBB - get a Samco one - or if you've got the money get an APR bipipe)

[BigDaz]

If your talking about the clips for the small vaccum hoses the just use cable ties on them this is what I've done after i replaced my DV's etc after suffering a similar problem.
I'd also suggest getting it along to MRC for a health check if your still having problems

No, I think he meant the main boost hose which feeds the turbo with air.
Prob 2" diam or more I would have thought
MRC would be good, but I live in north scotland so a bit of a trek.

I have a catch can left over from Scooby days so I may use that, I have a copper type T piece which I might use to replace the F pipe, or as I said just delete it altogether

Daz

[ZeroK66]

Mate- I wouldnt be driving the car hard - if you do have a boost leak and you over spin one a them turbos it will go pop and it will be time to shell out stacks a cash!

Hope ya find the leak, easy enough if you know where to look

[BigDaz]

Mate- I wouldnt be driving the car hard - if you do have a boost leak and you over spin one a them turbos it will go pop and it will be time to shell out stacks a cash!

Hope ya find the leak, easy enough if you know where to look

Ok, just back in from garage, TBB has a split in the bottom underneath the jubilee clip, f hose looks OK.
Will it still leak from under the clip?

I presume if the turbos havent gone up till this point & I take it easy from now on I "should" be ok?
If I have no boost pressure how can the turbos overspin? surely they are not doing much at all?

[ChipHazzard]

yes is the answer to that question, another culprit could be the N75

[dummi]

Mate- I wouldnt be driving the car hard - if you do have a boost leak and you over spin one a them turbos it will go pop and it will be time to shell out stacks a cash!

Hope ya find the leak, easy enough if you know where to look

If I have no boost pressure how can the turbos overspin? surely they are not doing much at all?

Zerok66 would the wastegates not open beyond a point and save that happening?

[KayGee]

With a split you don't have closed loop wastegate control because the system is effectively open loop. Hence system shuts down (limp mode) to protect the turbos.

[ZeroK66]

Mate- I wouldnt be driving the car hard - if you do have a boost leak and you over spin one a them turbos it will go pop and it will be time to shell out stacks a cash!

Hope ya find the leak, easy enough if you know where to look

If I have no boost pressure how can the turbos overspin? surely they are not doing much at all?

Zerok66 would the wastegates not open beyond a point and save that happening?

My limited understanding is that the engine requests a level of boost but does not get it and so keeps the wastegates shut and the turbos keep spinning quicker and quicker trying to deliver the level of boost the ECU is asking for - turbos can be pushed too far and you run a bearing.

I think the main problem is that with a boost leak the turbos simply have to work MUCH harder to achieve the same level of boost - this stresses them and they can fail because of this.

Take it easy - if you are replacing the TBB, replace the F-Hose at the same time. They are so cheap. make sure the clamps are not over tightened and get the inlet pressure tested to make sure all is well once its all been fitted.

Good luck mate

[Dr-Al]

I think that, if the deviation between requested and actual boost is larger than a certain amount, the car will revert to limp mode. There are many DTCs that will cause the ECU to do this (including the fuel trim - Lean).

In limp mode, the car will not request more than 0.4Bar boost. Even so, to produce a 0.4Bar boost in a leaky system, the turbos will be working extra hard because much of the effort is going to waste (being vented through the leak rather than being pushed into the engine).

This means that (potentially - depending on the size of the leak) your turbos are working as hard to maintain the 0.4Bar during general 'pootling' driving as they would be if you were to take it onto the race track and drive it hard.

My advice would be to get it fixed ASAP, even if this means wrapping it up with electrical tape until you can get it to a garage.