Loss of Full Boost Pressure

[c3nturi0n]

any tips or hints?

Cheers.

[Toady1]

Mines also losing full boost. I can hear a hissing noise coming from the rear of my engine around the RS6 oil filter cover area. I'm going to look into this area at the weekend as I'm convinced I've a vacuum pipe that has split or come off causing my issues as I've got no fault codes on VCDS. I assumed it'd be an N75 valve but they are working fine according to VCDS. The car is new to me so I dont know if the hissing noise is normal or not in that area, I can't see why it would be. I checked all my boost pipes and tightened them up at the weekend, but they were all fine.

[Toady1]

Found my fault this evening! A split PCV pipe at the rear of the engine. Went to remove the pipe from the rocker cover and the whole thing snapped off in my hand. Tried to use insulation and duck tape to see if it fixes it and it did 99%. Still leaks as it is under a fair bit of pressure, so need to source a new pipe, but hissing sound is pretty much gone and full boost is restored.

[c3nturi0n]

cheers... onto a DIY tonight if I get time

[Toady1]

I had no codes with mine on VCDS.

[ATinOf]

This gets brittle and snaps easy. You sure its your problem and not another one youve created?

If this is the PCV return to the oil tank breather Ive got one of these that has been DIY repaired if you are interested for a fee. I will find an image of it for you.

[ATinOf]

Found my fault this evening! A split PCV pipe at the rear of the engine.

If this is the PCV return to the oil tank breather Ive got one of these that has been DIY repaired if you are interested for a fee. I will find an image of it for you.

Here you go - my damaged pipe, clean break


And my double heat shrink repair


This was subsequently replaced with a new one but worked fine while it was on temporarily;the new one obviously comes with the other 2 pipes heatshrunk to it as an assembly which is why its steep - GBP102.00 plus VAT
Part ref; 07L 103 542A

Make me a reasonable offer to make it worthwhile me parting with this emergency spare and its yours, bear in mind mine also comes as the whole 3 pipe assembly

[Toady1]

Hi, I bought a full assembly from Audi yesterday for as you say.....£128! Also a new A/C pressure sensor as that's also gone. I'm hoping that this is my fault. As you say these pipes become very brittle due to age and heat, and they get disturbed when oil changes are done to access the oil filter. So there is most likely further breaks somewhere which is why I just bought the whole assy. I also did a very similar repair to my pipe as you did with some reinforced marine pipe and heat shrink. But I can still hear (albeit quieter) a hissing noise, hence thinking I have another leak. I'm pretty sure this is my fault.

Edited to add - I've not fitted this yet but not 100% convince it is my loss of full boost fault. I'm kind of swaying toward a DV fault now. Will report back when I've done more investigating!

[c3nturi0n]

Any luck with fault finding and resolution?

[Toady1]

Any luck with fault finding and resolution?

Wow thats an old post I'd forgotten about. I think I had a dodgy N249 valve. I disconnected the electrical connector and refitted it and it seems to have cured it. I did replace the BOV for Forge items. I also replaced a load of vacuum lines during the process. I do still get a symptom of loss of full boost every now and again, so it could be that I need to renew my N249, but they are on back order so god knows when I'd get a new one.

I've also since then replaced all spark plugs, originals were perfect. I've also bought two noew N75 valves to replace when Iget the chance as I think they are a bit old now and may not be working as well as they should. So...to answer your question, I'm not really sure I've got to the bottom of it, but I don't think I'm losing full boost. If anything....I'm just used to the power.

Sometimes it does seem to fail to boost hard, but I may just be imagining it. I can be driving along in auto mode put my foot down a bit, nothing really happens, put my foot down a bit more, and nothing again, until I put my foot down lots more, and then the revs will pick up and it'll boost. Almost like the throttle body fails to open, to the turbos can't spin up and create boost. Or, my other hunch was N75 valves mechanically sticking, hence buying some to fit. They look a real PITA to replace btw! But oddly if I drive it in manual mode it never acts like this. This could also be linked to the N249 of course. VCDS shows no faults at all.

[c3nturi0n]

Any luck with fault finding and resolution?

Wow thats an old post I'd forgotten about. I think I had a dodgy N249 valve. I disconnected the electrical connector and refitted it and it seems to have cured it. I did replace the BOV for Forge items. I also replaced a load of vacuum lines during the process. I do still get a symptom of loss of full boost every now and again, so it could be that I need to renew my N249, but they are on back order so god knows when I'd get a new one.

I've also since then replaced all spark plugs, originals were perfect. I've also bought two noew N75 valves to replace when Iget the chance as I think they are a bit old now and may not be working as well as they should. So...to answer your question, I'm not really sure I've got to the bottom of it, but I don't think I'm losing full boost. If anything....I'm just used to the power.

Sometimes it does seem to fail to boost hard, but I may just be imagining it. I can be driving along in auto mode put my foot down a bit, nothing really happens, put my foot down a bit more, and nothing again, until I put my foot down lots more, and then the revs will pick up and it'll boost. Almost like the throttle body fails to open, to the turbos can't spin up and create boost. Or, my other hunch was N75 valves mechanically sticking, hence buying some to fit. They look a real PITA to replace btw! But oddly if I drive it in manual mode it never acts like this. This could also be linked to the N249 of course. VCDS shows no faults at all.

Thx. Mind me asking what n249 is for and where is it placed?

Ps. Mine runs superbly but every now and then i get this intermittent error that bugs me and would like to get to the bottom of it.

Other point i noticed recently is that the car would at times get kind of rough for a split second or two (almost misfire like) and then would boost like a rocket at full throttle . As you said, no errors per se hence i’m puzzled really where to start!

[Toady1]

The N249 solenoid controls the bovs, it is located at the front of the engine under the v10 cover which if you pull towards the front of the car inline with the engine will come off its mounts.


Have you connected up VCDS to see what the misfire count is like?

[c3nturi0n]

Thx.

No errors in VCDS unless there is specific place to look for them?

[Toady1]

No I didn't mean look for errors. You can run the diagnostics to monitor misfire value. I cant remember off the top of my head what the look up value is, possibly 170, 171, 172 on the output tests.

[c3nturi0n]

No I didn't mean look for errors. You can run the diagnostics to monitor misfire value. I cant remember off the top of my head what the look up value is, possibly 170, 171, 172 on the output tests.

Cheers... under Engine or Engine II i suppose?