RS2 with a boost leak . . .

[Golfboy666GTI]

Firstly, I havent been able to get the car scanned, but I thought Id ask if some of you experts may be able to help me.

My RS2 has just started boosting to only 10/11psi.
It idles smooth, has 4 year old Roose Motorsport boost pipes and a new turbo 2 years ago. When on boost/WOT the car performs like it used to till it hits 10/11psi (and stays there), normal driving you dont notice that anything it wrong.
Any ideas what the issue could be?

[bertman]

WGFV fooked?

[Golfboy666GTI]

Yeah, thats what I was wondering. If the N75 WGFV isnt working it should be running mechanical boost from the WG spring, around 0.6 Bar so that would be my 10psi Im getting at the moment.

If I unplug the N75 then the car should continue runing 0.6 Bar?

[tscheel]

Yeah, thats what I was wondering. If the N75 WGFV isnt working it should be running mechanical boost from the WG spring, around 0.6 Bar so that would be my 10psi Im getting at the moment.

If I unplug the N75 then the car should continue runing 0.6 Bar?

Yup - or WG spring pressure anyway. It's about .5 on my S2.

[Rusty]

That's not a boost leak causing the drop in pressure. Unplug your MFTS (big brown plug under the inlet manifold) and try it then.

[mike74]

...or ambient pressure sensor needs 're-calibrating'. When mine boosted low last year that's what was wrong...

[UrS4boy]

When on boost/WOT the car performs like it used to till it hits 10/11psi (and stays there), normal driving you dont notice that anything it wrong.
Any ideas what the issue could be?

Nik: I would start with checking the N75 WGFV, i.e. unplug it and see if there is any change. Normally, there would be a change, if not, either the WGFV is not working or the ECU isn't getting the boost signal that it needs to control the WGFV. This relates to the moisture trap.

N75 info: http://forums.quattroworld.com/s4s6/msgs/20987.phtml

Moisture trap info: http://forums.quattroworld.com/s4s6/msgs/20401.phtml

Electrically checking the N75 WGFV:

http://www.sjmautotechnik.com/trouble_shooting/ecuf20v.html#outs4

[Golfboy666GTI]

Nik: I would start with checking the N75 WGFV, i.e. unplug it and see if there is any change. Normally, there would be a change, if not, either the WGFV is not working or the ECU isn't getting the boost signal that it needs to control the WGFV. This relates to the moisture trap.

N75 info: http://forums.quattroworld.com/s4s6/msgs/20987.phtml

Moisture trap info: http://forums.quattroworld.com/s4s6/msgs/20401.phtml

Electrically checking the N75 WGFV:

http://www.sjmautotechnik.com/trouble_shooting/ecuf20v.html#outs4

Thank for that Dave.
Ill try unplugging the N75 after work.
I read your moisture trap article, if this is the issue I just drain it and refit it?

[UrS4boy]

G71 Manifold Absolute Pressure (MAP) sensor information

Thank for that Dave. Ill try unplugging the N75 after work. I read your moisture trap article, if this is the issue I just drain it and refit it?

The moisture trap issue is usually the hose from the intake manifold to the moisture trap become disconnected at the moisture trap (or *AFTER* the moisture trap) and the MAP sensor inside the ECU doesn't get any boost signal = even if the WGFV is working, the ECU will not control it and all you will get is WG spring pressure.

G71 Manifold Absolute Pressure (MAP) sensor information:

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

[Golfboy666GTI]

I unpluged the N75. No change at all. Boost is still 10-11psi.

[Rusty]

Have you tried the MFTS yet?

[Golfboy666GTI]

Have you tried the MFTS yet?

I'll give it a go tomorrow. What should I expect from doing this?

[Rusty]

The boost to come back!

[UrS4boy]

I unpluged the N75. No change at all. Boost is still 10-11psi.

To me, that implies that the N75 is not functioning. This could because:

1. N75 is Fubar'd: http://forums.quattroworld.com/s4s6/msgs/20987.phtml

2. Wiring to N75 from ECU is Fubar'd: Checking the ECU connection to the N75:

Output tests:
a) http://www.sjmautotechnik.com/troubl...f20v.html#out3 *OR*
b) http://www.sjmautotechnik.com/troubl...20v.html#outs4

One video: https://www.youtube.com/watch?v=SNwqbyQZzfY

3. Boost hose signal from intake manifold to the MAP sensor in the ECU is Fubar'd

4. As Rusty says, the MFTS might be failed and telling the ECU to limit the boost. On the ABY/ADU, the MFTS is connected to the ECU via pin 46 of the T55 ECU connector. Using this pin as a high temp alarm (> 119 C) - the ECU cuts off active boost control as a safety measure.

http://forums.quattroworld.com/s4s6/msgs/22584.phtml

[Error404]

10-11psi is a little higher than spring pressure should be, but not much maybe your gauge is not accurate, or you might have a non-OEM WG spring.
MFTS fault will cut boost to spring pressure, as will a knock sensor fault.
Other than that, you probably have an issue with the N75 or its wiring or maybe the MAP sensor isn't able to read correctly due to a blocked line or similar.
I wouldn't bother guessing, pull the codes and go from there.