Intermittent Turbo Pressure? Audi urS6 Avant auto

[bigtalljim]

Just back from Le Mans and filled up with 98 ron french fuel. Car decided to give me restricted boost. Got back to GB and filled up with shell and got full boost back. Yesterday it did it again for half hour. Turned it off at mates and 2 hours later back to full boost.

Any idea what is happening and why?

[Yertis]

Dodgy by-pass valve, it's almost certainly something between turbocharger and inlet manifold, boost control type of thing.

[bigtalljim]

I think the boost control os electronic from the ecu. Something telling it to give only limited boost now and again. Did it again after short trip of 10 miles and refuel. Seems to be when it heats up, catalyists or some sensor?

Realy annoying, will plugging it in to machine tell me?

[istoo]

http://forums.quattroworld.com/s4s6/msgs/22625.pht...
The N75 controls the boost as well, it is electronically linked and in the right sort of place and can get sticky when they begin to fail. And can be intermittant, funnily i am about to replace mine as well as its a bit suspect...

how much off boost was it? totally off boost? if totally have a look atht emoisture trap right at the back of the bulkhead with the thin ie 1-2mm vac lines either side they are prone to "popping" off.

Edited by istoo on Wednesday 16th June 20:34

[Yertis]

istoo said:

http://forums.quattroworld.com/s4s6/msgs/22625.pht...
The N75 controls the boost as well, it is electronically linked and in the right sort of place and can get sticky when they begin to fail. And can be intermittant, funnily i am about to replace mine as well as its a bit suspect...

how much off boost was it? totally off boost? if totally have a look atht emoisture trap right at the back of the bulkhead with the thin ie 1-2mm vac lines either side they are prone to "popping" off.

Edited by istoo on Wednesday 16th June 20:34

But they tend to stay popped off. I think it's yer N75 thingy, most likely.

[istoo]

maybe the N75 doesnt speak french?

Edited by istoo on Thursday 17th June 10:52

[Dr G]

istoo said:

maybe the N75 doesnt speak french?

Edited by istoo on Thursday 17th June 10:52

Or perhaps it is French and has gone on strike?

[bigtalljim]

Found out that boost ok at lower outside temps, was fine last night on drive home. But in heat of the day it plays up.
Is this pointing to Air Flow meter as hot air goes in?
Can i clean it up, looks fragile that thin wire.

Or is this pointing to air intake temp switch on throttlel housing?

Edited by bigtalljim on Wednesday 23 June 09:51

[Robatr0n]

I had a similar problem and it turned out to be a dodgy boost hose running from the rear of the Inlet Manifold to the ECU.

Also, may be worth changing your Wastegate Frequency Valve.

[bigtalljim]

Its only doing it now when the outside air temp is warm.
If drive at night or early morning when air temp is cool then ok?
does this point to any particular sensor?

[Robatr0n]

That does make it sound like a sensor.

Have you run you car hot, turned it off and turned it straight back on to see what the boost does? May be worth unplugging the MAF once the car is warm to see what effect that has.

Edited to add:

If you do decide to clean the MAF, the best way would be to buy yourself some IPA cleaner (Maplins sell it) and pop IPA in a bowl along with your MAF. Make sure you don't get the plugs wet and try to submerge the hot wire in IPA to clean all the muck off. Don't pour anything through the MAF to clean the wire as it may break!

Edited by Robatr0n on Friday 2nd July 13:44