Boost loss after 4000 rpm’s

[Jackson88]

Hey, I’m somewhat new to the VW world. I have a 2008 GTI that I just had a turbo replaced on. I just replaced it with a stock turbo. Now as soon as I hit 4000 rpm’s, I lose boost. But if I turn the car off and then start it again, I get boost back until I go over 4000 rpm’s. I could use some advice on where to start looking for what’s causing it to do this.

 

[BurgerGuy]

If your car has an engine cover does it say FSI or TSI? Model year '08.5 and up for the MKV is equipped with the EA888 gen 1 TSI. Some other questions...

• Does the car throw a CEL? Does it flash or stay on?
• Has the car been scanned for codes with VCDS, by the shop who did the repair, or a dealership?
• When you lose boost at 4000 RPM does the car fall into limp mode where it drives slow until ignition is cycled?

 

[Jackson88]

It’s the FSI engine, CEL was not cleared cuz I had someone I know swap it out cuz I couldn’t afford the garage price. Idk if I would call it limp mode cuz it drives like it should just no boost until I turn it off and start it again. I plan to get the CEL cleared to see what they are. The light doesn’t flash tho when the boost gives out. It just feels like I lose all boost.

 

[ROH ECHT]

You should confirm the WG and N75 all work.

But more importantly; Scan for stored engine Fault codes...only emission and safety faults cause a CEL. Post all engine codes you see stored. Would be good to have the mileage stamp for each code so people here can see old codes to new codes.

This may have nothing to do with the turbo function...and may be fuel related. I.e., it can go into 'safe' mode for a failed cam follower or the low fuel pressure (thrust) sensor.

 

[JerichoSamurai]

Ik this is kinda out there but it's possible your diverter valve is shot and can't withstand air pressure beyond 4000 RPMs and just flies wide open and lets all the boost leak out. Is there any sort of audible sounds when you start to climb above 2000 RPM?