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The N75 compares the ambient air to the compressed air from Turbine side (cold side) and adjusts boost accordingly. If you have a leak in the line going to the cold side from the N75 the sensed pressure will be lower than actual and the Turbos will try to overboost for a few seconds then the ECU will detect it, through the MAP sensor I think and will cause limp mode or just plain reduced boost.

I had this happen on my Audi RS6 which also uses Motronic 7.1.1.  Had just did an engine pull & replace, then had a custom tune and I started asking the guy for a tune with less boost. He gave me a custom tune or two with lower boost but said most other RS6's were using more boost than I asked for and weren't having a problem.  I started thinking N75, used a spare to no avail, then used my Snapon video scope and started scoping the lines to the Turbos, they went from the N75 to a Tee then went to each Turbo, one was completely disconnected so the line was using ambient air or something in between due to one side being disconnected. Hooked up the line and all was well.  While it was happening it pulled like a beast for a few seconds before limp mode kicked in.

Edited by hahnmgh63
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@hahnmgh63 thank you very much Mark. 

Ok i will need to crawl down and disconnect and check all pressure lines again. MUST be somewhere there the fault. 

 

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7 hours ago, ekstroemtj said:

I am pretty sure the noise/ pressure relief is coming from the passenger side. Driving through a tunnel with open windows make me believe it's something on the right side.
Seal on lower tube is changed

Pressure hose to wastegate changed

Is it possible to get access to the wastegate linkage like on the picture (pics from member @danyol)

 

There is another pressure hose which is going from n75 to charger housing.

Measuring what?  Blowing through this pipe makes air escaping at the end of the air tube which ends in the air filter housing.

 

I have tried to get to the wastegates as well, with no luck. Can’t even figure out where to blindly spray WD40 to try and get them to work smoother. If you get any insights please let us know.

For your sound, I recorded video of my turbos kicking in and the wastegate opening for comparison. It will take a while to process them but I will post them soon.

 

 

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Here is the video; the exhaust gets loud so it is easier to hear under partial acceleration, and when going up hills and such. Just some samples of the whooshing sound of the turbos, and then the sound of the wastegates after. I marked where the wastegates make a weird sound, but it’s like a wheeze rather than a bark. If anyone knows what makes them sound like this I’d appreciate suggestions. I’m thinking it is the diverter valves not working quite right. Or any other comments on the sounds, thanks. I know it's slow (last one is actually WOT).

 

 

Thomas, listening to your sound again, it must be a pretty big leak to sound like that, if it is the turbo system.

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Mike you treat your beast very hard :-) if I am doing so my boost will hit the sky.

 

I need to figure out how to get access to WG. Difficult and nobody here knows looks like.

I am not Shure if the noise in your video is the WG or DV Valves

 

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I wish my boost would hit the sky! Well, I guess not really. I see why you have a bad problem then. So you think that is the diverter I am hearing. Someone else said that too. Off to buy one then!

 

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8 hours ago, Zakowsky said:

Here is the video; the exhaust gets loud so it is easier to hear under partial acceleration, and when going up hills and such. Just some samples of the whooshing sound of the turbos, and then the sound of the wastegates after. I marked where the wastegates make a weird sound, but it’s like a wheeze rather than a bark. If anyone knows what makes them sound like this I’d appreciate suggestions. I’m thinking it is the diverter valves not working quite right. Or any other comments on the sounds, thanks. I know it's slow (last one is actually WOT).

 

 

Thomas, listening to your sound again, it must be a pretty big leak to sound like that, if it is the turbo system.

Mike it sounds to me like your leaking boost around the DV itself. Now the only way this happens is the diaphragm is split or the changeover valve positive pressure isnt getting to the DV to hold it shut and stop it opening early and bleeding off your boost back around into the turbo intake. Either that or a boost leak which isn't consistant with your noises really. 

Have you got drop in air filters or intake ? Makes a lot more induction noise than mine did. I could barely hear my intake or turbos at all. It was a unified roar and go type affair. Yours also doesn't boost very high and its sporadic, sometimes boost is looking ok sometime weak. That either the DV's leaking or the wastegates opening before supposed to. 

If this is your original DV's then replace 710p and also the vac pipes from the changeover valve all the way past bank 2 and into the Tee and down each side to the DV's. 

 

Just in case there is some confusion about the what the changeover valve does here is my quick explanation. 

 

1. Off throttle ..  .vaccum in manifold change over valve is pulling the DV's open. This is bypassing any boost from the turbo outlet side to stop it from stalling or surging. This reduces turbo lag when you accelerate again. 

2. Part or full throttle the boost pressure inside the manifold is diverted through the changeover valve to each DV to push and help hold closed the DV assisting the spring which is also holding it closed but isn't strong enough to resist the boost alone. (And if you make the spring too strong the vaccum can't open the DV when you lift of the throttle..  Makes sense init). 

 

The fact you have weird boost, low sometimes tells me the diaphragm is split on one or more or the delivery of the changeover valve pressure is not getting to the DV (like a broken vac pipe or changeover valve fault. 

 

When I bought my ctt it had 0.6bar, replaced both DV's and got 0.8bar +. Infact one was split one was fine. 

 

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Glad to see you are going to still stop by Lewis! I actually just stepped in from the garage, retesting the diverters. Lines are all good but the passenger side one does seem a bit different than the driver’s side. The driver’s side snaps back firmly; the passenger side feels a bit mushy and makes extra noises. Not as clean a snap. The line running from the Tee to the back is one way and seems to hold fine when reversed. I guess that goes to the manifold eventually, I sucked up some nasty tasting crap!

 

I am skipping work and heading to Porsche - they have one in stock and a week to order the other. Just in time before we leave.

 

Edit - Btw I do have a cold air induction with Evo filters, you hear much more with them.

 

Edited by Zakowsky

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43 minutes ago, Zakowsky said:

Glad to see you are going to still stop by Lewis! I actually just stepped in from the garage, retesting the diverters. Lines are all good but the passenger side one does seem a bit different than the driver’s side. The driver’s side snaps back firmly; the passenger side feels a bit mushy and makes extra noises. Not as clean a snap. The line running from the Tee to the back is one way and seems to hold fine when reversed. I guess that goes to the manifold eventually, I sucked up some nasty tasting crap!

 

I am skipping work and heading to Porsche - they have one in stock and a week to order the other. Just in time before we leave.

 

Edit - Btw I do have a cold air induction with Evo filters, you hear much more with them.

 

Passenger side is a piece of cake to replace, lucky you. Driver side is a bit of a chore. 

Passenger side just unscrew a few torx screw on the wheel arc front part and pull back to see the DV. Only need water pump pliers to change it out. 10 mins and you'll be out for a test drive lol

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Checking the lines going away from n75 valve again. I can bet the pressure lines to wastegates are very tied. The line which is going to the cold side of the charger how Mark call it, i am not shure. I squeezed the line with the zip tie. Almost closed. Wanted to see what happens if the air stream to the valve / from the valve is different.   Went for a test drive just to see if something changed.  It did interestingly.  I hope i am not paranoid but the way how the car is acting is different during acceleration. I will change this pressure line these days and report back what happens.

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Edited by ekstroemtj

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Thomas, this is a great diagram to explain how this system works (originally from Paul N. of S2Central.net). It’s based on a VW system so pretty much the same as ours. The “hot” side of the turbo is the one with the turbine, named obviously as it is spinning from the hot exhaust gases. The “cold” side of the turbo is the one with the compressor, which compresses the air coming in from the intake air filters. The diagram shows how this works; when boost is turned on, pressure from the output side of the cold side of the turbo (so the dark blue compressed air region) goes into the N75 valve and is dumped back into the cold side before the compressor (light blue). So if you blow into the one that goes to “atmosphere” (the light blue side of the cold side), it will blow out the air box. If you blow into the line to the N75 that goes to the compressed air side of the cold side (dark blue) it will have a bit more resistance when the engine is off, but pressurized air will blow out of it if the engine is running (which you wouldn’t want to do!).

 

When the boost pressure gets too high the N75 valve opens and sends the pressurized air from the compressed air side of the cold side of the turbo to the wastegates to open them. In practice it doesn’t actual just open, it pulses very fast to maintain a certain level of pressure to the wastegate actuators.

 

So if I am reading correctly Thomas, you have restricted the line that goes to the dark blue, compressed air side of the cold side of the turbo. This is the line that provides the pressure to open the wastegates, so in fact it should actually increase the chance of an overboost condition. Let us know how your tests go!

 

BoostPressureControlShowingBPVandWGFV_LargeRev1.jpg.236abc11af12390fc1ffb23f0dea1ca8.jpg

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First of all thank you very much Mike for your detailed post.  

There are 2 lines in direction to the passenger turbo. One to the wastegate, one to the turbo housing . I am talking about line 10 which is measuring the ambient air. This one i squeezed, hope to reduce the air flow to n75 and see some changes.  Weekend i will check this entire line down where its connected. Hope to find a leak

image001.png

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9 hours ago, ekstroemtj said:

First of all thank you very much Mike for your detailed post.  

There are 2 lines in direction to the passenger turbo. One to the wastegate, one to the turbo housing . I am talking about line 10 which is measuring the ambient air. This one i squeezed, hope to reduce the air flow to n75 and see some changes.  Weekend i will check this entire line down where its connected. Hope to find a leak

image001.png

Thomas if line 10 is broken or leaking you will have overboost! I found mine was very brittle hard and cracked where it connects to the turbo at hose clamp 8. 

You said it was ambient air, this is not correct, it is the compressor outlet "boost pressure reference" for the n75 to use to control the boost curve and maximum boost allowed.

This is the only way the boost is controlled to stop peaking over the "requested boost" and thus if it boost too high it will pop the overboost code. 

 

Bit hard to access it, I repair mine whilst doing the alternator twice. 

I think removing the air box and inner Wheel arc cover plastic will give you some access to get access, then maybe the turbo intake pipe will also need to be removed. 

I took pictures of the this and posted it I'm sure! 

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@ Lewis . Thank you for taking care. 

Yes I remember the hose is a little bit hidden and difficult to get to. I will inspect and try from up or underneath. I will take pictures.  Boost pressure reference hose ! Thankx for technical lesson.

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58 minutes ago, ekstroemtj said:

@ Lewis . Thank you for taking care. 

Yes I remember the hose is a little bit hidden and difficult to get to. I will inspect and try from up or underneath. I will take pictures.  Boost pressure reference hose ! Thankx for technical lesson.

Found the picture. 

See the pipe where it is clipped to the alternator and then connects the the turbo, that is part number 10, boost reference. 

You most probably have to remove the turbo inlet plastic pipe part number 3 in the second picture attached and the hose to be able to get access to the clip and replace that boost reference pipe. 

Screenshot_20170811-111459.png

Screenshot_20170811-112142.png

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Very good picture. Thank you.

I see you take away the connection piece - part no. 3 - which has a gasket.

I don't have this gasket and can't get it until tomorrow. I will see if I can manage to change the pipe without removing the plastic part no. 3

 

Edited by ekstroemtj

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Great discussions here, yes, a plugged or disconnected line should and will cause an quick overboost before the ECU shuts it down with a fault/limp mode. Keep in mind that lines (picture above) 10 and 5 (from each Turbo) go to a Tee before connecting to the N75 valve. So line 10 may be Ok but line 5 may be the problem. This is where my portable Snapon Bk6000 video scope saved me on my Audi.

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1 hour ago, hahnmgh63 said:

Great discussions here, yes, a plugged or disconnected line should and will cause an quick overboost before the ECU shuts it down with a fault/limp mode. Keep in mind that lines (picture above) 10 and 5 (from each Turbo) go to a Tee before connecting to the N75 valve. So line 10 may be Ok but line 5 may be the problem. This is where my portable Snapon Bk6000 video scope saved me on my Audi.

Not strictly true. Line 10 goes direct to the n75 valve without a T.

Indeed line 5 goes to a T before it goes to each wastegate actuator. The bleed off turbo reference air return pipe (part of part 14 the top vac pipe) from the other n75 port goes back down to the right side and re-enters  the "closed measure air" system. Even if this pipe is broken it won't cause overboost maybe some idle or lean adaption at worse, it's effectively a vacuum leak. 

So to clarify pipe 10 needs to be not blocked and not leaking so the n75 and Ecu can do its job to use the wastegates to control boost smoothly and not overboost. 

You can get overboost code if the map sensor is disconnected also. So don't rule this out as possible component failure or wiring/ plug issue. 

Screenshot_20170812-073909.png

Edited by lewisweller

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On 29.7.2017 at 11:24 PM, ekstroemtj said:

If someone need a membrane for this crankcase ventilation..

 

They have it on sale now. I bought some just to have it if needed.

 

Porsche sells just the entire unit which is expensive.

 

https://vanos-bmw.com/product-category/porsche

 

 

 

Came today. Just bought it in case i need.

 

post from russia. One week. 

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To get access to the small pressure tube i disconnected all this stuff around. Airbox. Tube with the MAF. Tubes which are going to turbo charger cold side outlet. But, this small tube is hidden and i can hardly get my hands to the end where its connected to the Charger housing. No way to change this. Try from up and down and from wheel well. Nothing. 

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1 hour ago, ekstroemtj said:

To get access to the small pressure tube i disconnected all this stuff around. Airbox. Tube with the MAF. Tubes which are going to turbo charger cold side outlet. But, this small tube is hidden and i can hardly get my hands to the end where its connected to the Charger housing. No way to change this. Try from up and down and from wheel well. Nothing. 

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Thomas remove the air box completely. Then you can have straight through access. It the same place I took the picture from. 

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Thank you for this info. Hope not to difficult to take out the filter housing. After you go through wheel housing?

tomorrow if there is time will check the driver side down at the wastegate. 

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38 minutes ago, ekstroemtj said:

Thank you for this info. Hope not to difficult to take out the filter housing. After you go through wheel housing?

tomorrow if there is time will check the driver side down at the wastegate. 

Easy yes. One 10mm bolt at the top and the. Pull up and out towards the engine and out towards you. 

Access via the wheel arc. 

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I may have been mistaken quoting the diagram number Lewis. Are you saying that Porsche has chosen to only to only sense off of one Turbo?  On my Audi with ME7.1.1 both wastegate hoses go to a tee then onto the N75 and both Turbos have a sense line that tee's then goes onto the N75.

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3 hours ago, hahnmgh63 said:

I may have been mistaken quoting the diagram number Lewis. Are you saying that Porsche has chosen to only to only sense off of one Turbo?  On my Audi with ME7.1.1 both wastegate hoses go to a tee then onto the N75 and both Turbos have a sense line that tee's then goes onto the N75.

Yes, it senses from the passenger bank 1 turbo only. There is no pipe to the drivers side turbo. 

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