No Boost.......Help :-(

[Varks]

Not been on in a few years, gone from B5 S4 ownership to C5 RS6, picked up a project from one of the members on here, have been working my way through a few issues, brakes, head lining, O2 sensors etc, so now have no engine fault codes and since changing out no 2 O2 sensor in bank 1 i am returning 20MPG instead of the 10 i was getting previously,
Although i still have no boost pressure, maybe getting 3PSI, I was hoping it was down to the faulty O2 sensor but it would seem not,
I have just done a PX test and it holds pressure with no problem, pressurising from one of the intakes, i have swapped out the DV's as i had some spare and also swapped out the N75,
I have a mitivac coming today so i can check the vac hoses to the wastegate actuators and also have new silicone hoses arriving as i will replace anything that looks a little suspect,
What is my next move? a friend has mentioned the non return valves in the vac system that sit under the intake manifold, apart from that i am a bit stumped,
I will get Vagcom fired up in the next couple of days and do some log runs, so i can see what the demanded boost is like against actual,
Anyone know of any common culprits that could cause the loss of boost? apart from that the car runs rally well, no misfire, no shaking at idle,
Any suggestions will be greatly appreciated,

[Shoppinit]

Hard to say without knowing what the ecu is asking for. Could be a multitude of things from mechanical blockage of the turbos to a bad EGT.

Might as well wait for the Vagcom to have an oriented approach.

[Varks]

Yeah will get that sorted in the next few days and see what the ECU is demanding, I did have an issue with the EGT's on my B5, although it put it into limp mode i did still have some boost, albeit minimal,

[Shoppinit]

Could be a vac leak at the waste gates, or maybe bad plumbing around the N75 is the engine has been messed around with before you got it. Could even be a botched map.

[Marcin]

I know it might sound basic but... did you try disconnecting the battery for 15min? My one had occasional issues with EGT readings resulting in a reduced boost to 0.3bar Only disconnecting the battery worked

[Varks]

Marcin, car came to me with a completely flat battery, so have fitted a brand new one, i'm going to try and get out and do some log runs and see what's going on, been a few years since i have done any so may take me a while to get back into it lol,
I have a mitivac now too, so hopefully i can eliminate leaks in the wastegate lines, also have new 4mm vac lines but think it may be too small for some of them, have new non return valves on the way for the various ones around the intake manifold as well as the Y one and a new check valve breather hose assy just in case,
on a different note the metal coolant pipe that runs across the back with the coolant temp sensor in it and runs to the top of the rad is very corroded, so will whip that off and fit the replacement i have for that too with new o'rings, try and make sure i don't need to strip it down for a while,
I did have EGT issues on my B5 and ended up getting SID motorsport replacement circuit boards for them, can't remember if they threw a code of not though, will see what they are saying on the log runs,
i've not driven it with any boost yet, so looking forward to getting to the bottom of it and seeing what she pulls like, supposed to be running 550bhp at 0.9bar