S3 massive under boost

[Lee Gerrard]

Hi all, new to the group and after some much needed help, my car is barely boosting, at 1st it was intermittent now it's full time, at around 2.5k revs you can hear air hissing out and there's practically no boost, there's no leaks as its all been checked, actuator is fine waste gate is fine and turbo is good! When you take the hose off the before the dump valve the car goes nuts! It's a ridiculous amount of boost but put the pipe back on an nothing again,no faults come up on the reader, it's had throttle pedal change, n75 valve, new dump valve, a bit stuck now? Anybody else had this issue before?? Please help!

 

[<tuffty/>]

Firstly I would scan for fault codes using VCDS... you can get VCDS cheaply for scanning fault codes and basic logging... info can be found in the FAQs thats in the stickies but here is the main thread..
http://www.audi-sport.net/xf/thread...lp-please-read-before-posting-updated.168407/

You can also see if there is someone local to you willing to do a scan by using the VCDS map thats in the VCDS section of ASN... VCDS will play a major part in fault finding on these cars

You then should consider having a smoke test done... this will find things such as split pipes etc as its not always easy to spot doing a visual check..

Some pics of the engine bay may help as it sounds like the hoses are connected incorrectly...

<tuffty/>

 

[badger5]

you hear air hissing out but no leaks?

hmmmm

smoke test it

 

[Lee Gerrard]

Thanks guys will try smoke test

 

[Essexman]

Sorry i know it sounds so simple, but check the tb- intercooler hose has'nt come off slightly at the intercooler end, i had same symptoms couple nights ago & thats what it was,

 

[badger5]

dump valve stuck open?

seen that... (Grrrrr)

 

[Lee Gerrard]

dump valve stuck open?

seen that... (Grrrrr)

Tried that 1st but thanks

 

[Lee Gerrard]

Intercooler seems to be a popular suggestion, will look into it. Thanks guys

 

[Lee Gerrard]

New update!! Had the car plugged in to vag com and it's saying car is 1.1 bar of boost when it's idle, and under heavy acceleration it goes upto 1.8/9, what's everyone's thoughts? Possibly boost pressure switch?

 

[<tuffty/>]

New update!! Had the car plugged in to vag com and it's saying car is 1.1 bar of boost when it's idle, and under heavy acceleration it goes upto 1.8/9, what's everyone's thoughts? Possibly boost pressure switch?

thats absolute pressure mind... need to extract atmospheric pressure from that value...

Is that requested or actual boost?

0.8/0.9bar of boost (12-13psi) is std boost pressure..

Need to log boost request as well as actual... this will be block 115 in VCDS

<tuffty/>

 

[Lee Gerrard]

My mistake, it's not as I said, it's 1 bar idle, on a mighty vac it only registers at 1.5 on full pressure when it should be around 3 bar, that's how the garage have just explained it to me, the lad yesterday got it wrong