Loss of Full Boost Pressure

5.0 V10 50v biturbo - 571 bhp
c3nturi0n
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Mon Oct 08, 2018 12:20 pm

any tips or hints?

Cheers.
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

Toady1
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Mon Oct 08, 2018 1:40 pm

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
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Wed Oct 10, 2018 10:34 pm

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.

Image
Image
Last edited by Toady1 on Tue Oct 23, 2018 1:28 pm, edited 1 time in total.

c3nturi0n
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Thu Oct 11, 2018 3:09 pm

cheers... onto a DIY tonight if I get time ;)
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

Toady1
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Thu Oct 11, 2018 4:31 pm

I had no codes with mine on vcds.

ATinOf
3rd Gear
Posts: 267
Joined: Fri Jul 06, 2018 7:32 pm
Location: Cheshire

Re: Loss of Full Boost Pressure

Post by ATinOf » Fri Oct 12, 2018 1:52 pm

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
3rd Gear
Posts: 267
Joined: Fri Jul 06, 2018 7:32 pm
Location: Cheshire

Re: Loss of Full Boost Pressure

Post by ATinOf » Fri Oct 12, 2018 7:31 pm

Toady1 wrote:
Wed Oct 10, 2018 10:34 pm
Found my fault this evening! A split PCV pipe at the rear of the engine.
ATinOf wrote:
Fri Oct 12, 2018 1:52 pm
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
Image

And my double heat shrink repair
Image

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
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Sat Oct 13, 2018 12:11 pm

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
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Sat Apr 27, 2019 9:31 am

Any luck with fault finding and resolution?
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

Toady1
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Sat Apr 27, 2019 10:08 pm

c3nturi0n wrote:
Sat Apr 27, 2019 9:31 am
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
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Sun Apr 28, 2019 10:01 pm

Toady1 wrote:
Sat Apr 27, 2019 10:08 pm
c3nturi0n wrote:
Sat Apr 27, 2019 9:31 am
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!
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

Toady1
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Mon Apr 29, 2019 8:03 pm

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
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Mon Apr 29, 2019 9:07 pm

Thx.

No errors in vcds unless there is specific place to look for them?
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

Toady1
2nd Gear
Posts: 223
Joined: Mon Jul 10, 2017 2:13 pm

Re: Loss of Full Boost Pressure

Post by Toady1 » Tue Apr 30, 2019 8:13 pm

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
3rd Gear
Posts: 266
Joined: Tue May 29, 2018 10:50 am

Re: Loss of Full Boost Pressure

Post by c3nturi0n » Tue Apr 30, 2019 8:59 pm

Toady1 wrote:
Tue Apr 30, 2019 8:13 pm
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?
2008 RS6 Avant (Monza Silver)
- Stage II MRC tune with gearbox (720PS/850Nm)
- MIJ Powerflow exhaust (non-res)
- H&R ARBs

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