Sporadic Boost Limitation 5 PSI / .3 BAR

[State'd RS2 Coupe]

Trying to sort a boosting issue. Assuming no leaks or other major issues as ½ the time I can pull full boost (25 PSI/1.7BAR) and maintain (22 PSI/1.5BAR) with no problems all trip long.

Other times I’m exactly limited to 5 PSI. No black smoke cloud overfueling problems, or any other noticeable engine hiccups, just sits at 5 PSI.

Stuck open wastegate? MAF going out? Searching the archives, but looking for leads to help narrow the search.

Pulling codes tonight.

Thanks.

[UrS4boy]

Trying to sort a boosting issue. Assuming no leaks or other major issues as ½ the time I can pull full boost (25 PSI/1.7BAR) and maintain (22 PSI/1.5BAR) with no problems all trip long.Other times I’m exactly limited to 5 PSI. No black smoke cloud overfueling problems, or any other noticeable engine hiccups, just sits at 5 PSI. Stuck open wastegate? MAF going out? Searching the archives, but looking for leads to help narrow the search. Pulling codes tonight.
Thanks.

Sounds like:the N75 wastegate frequency valve (WGFV) is not being activated properly by the ECU because the ECU is not getting the proper feed-back pressure at the G71 Manifold Absolute Pressure (MAP) sensor OR the ECU and MAP sensor ARE getting the proper info and the ECU is sending the proper signal to the WGFV but the WGFV isn't working properly or there is a flakey electrical connection OR there is an issue with a hose attached to the WGFV.

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

G71 MAP sensor info: http://forums.quattroworld.com/s4s6/msgs/20417.phtml

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

[State'd RS2 Coupe]

Could you be a bit more specific??

Thanks, you rock

[4WheelDrifter]

Once boost is limited does it come back while continuing to drive? Or do you have to reset the ignition toget the boost back?

[State'd RS2 Coupe]

Not 100% sure, but seems like I've had to restart to get it back. Generally when I've noticed it's always stayed limited. i.e. short drive to work in the morning, no go. Drive home and it works.

Cleared the codes out recently after some other work and didn't have an issue for a while, so will dump the codes again and actually take a look this time.

[Tonks4x4]

May be worth checking out your knock sensors too, make sure they are not cracked or the sheathing on the leads bare. This was giving me intermittent boost issues.

[prj]

Start with the basics.

1. Dump valve sticking.
2. Breather check valve at the back of the head sticking.
3. Check the timing, it might be 1 tooth out.

Then go to electronics...

[UrS4boy]

...2. Breather check valve at the back of the head sticking...

Huh? What breather check valve are you talking about? Item 20?

http://forums.quattroworld.com/s4s6/msgs/22506.phtml

[prj]

Yes