jw461

So my K04 allroad (bought pre-modified) never really ran as fast as I expected and I lived with it that way for the past year that I've owned the car. I recently got a VAGCOM as recommended and checked the requested/actual values. I don't remember what the numbers were exactly but they translated to about 18-19psi requested and 13-14psi actual at peak.

Anyway, next up is a boost leak check which I have much experience doing on Mitsubishi Eclipses/3000GTs and Toyota Supras. At first, I followed mostly the instructions everyone else follows, but I didn't like the air rushing out of the oil cap--I wanted total silence except leaks and for the system to hold pressure without additional air.

See attachment.

With this setup, I'm still getting a gurgle noise from the crankcase and the car won't hold pressure...it eventually leaks out after several seconds. I know, I've read over and over "that's normal" but where is it coming from? It's not blowby...I'm not even connected to the throttlebody, PCV, or any of the many vacuum hoses. Leaking past turbo seals? If so, how can that be normal? I've never heard that on any other cars.

Any other ideas on why my car isn't achieving the boost requested?

thejulex

Now, your problem is probably due to N75 valve, which is fairly common item to fail on stage 3 cars if never replaced since the car was made.

Each turbo has pressure reference line going back to N75, they merge and come to a barb on N75. From there the air can go two routes. Default one when N75 is not engaged is to wastegates. When engaged, the air goes to ambient (crankcase) to depressurize wastegates and raise the boost.

Broken N75 usually leaks air to ambient. Some new N75 will also leak some air to ambient, apparently the factory making these just plain sucks. This is where gurgling come from...

N75 is the brown plug part just north-west of your pressure gauge on the pic, half way between gauge and egr valve (silver cap valve), with horizontal plug. It is mounted right on top of manifold, wrapped in rubber sleeve and mounted to a bracket protruding from the manifold. It has three air lines.

Forgot to add that inlets also have air hookups but I am not sure where the lines go to.

jw461

Got it...I'll install a boost controller, set it not to exceed the requested boost level and see if that works. Hope it works.

jw461

Problem solved. Left the N75 plugged in, but capped off the ports. Added a MBC, did a few test runs to tune it and it runs great now at 18-19psi. Thanks for the help.