View Full Version : need help with overboost issue

05-27-2010, 12:46 PM
Does anyone have a diagram of the boost control system on these cars? I have the GIAC chip, and my car just started overboosting like crazy today. Gauge was reading 26-27 psi before I let off the throttle. No CEL and it didn't go into limp mode, just kept on boosting as far as I would let it. The only thing I've done to the car recently was a boost leak test, so I'm wondering if that stuck a valve closed or something... any ideas?

05-27-2010, 01:36 PM
Go race cars for money to help pay for the new turbo your gonna need.

05-27-2010, 01:37 PM
BTW thats sweet you have a 944 I want one soooo bad!!!!

05-27-2010, 02:26 PM
why would I need a new turbo? it's still boosting fine. also if you're looking for a 944 definitely get the turbo version, the N/A is slow as balls.

05-27-2010, 02:37 PM
Check the line between the N75 and wastegate actuator. Also check the operation of the wastegate actuator itself. And make sure the N75 is getting a boost source (should be from the compressor housing).

05-27-2010, 03:20 PM
I just checked and all the lines look good, and hose clamps are tight. How do I test the wastegate actuator?

05-27-2010, 03:47 PM
you can take the line off and put pressurized air to it. you should hear the wastegate actuator open/ close. it could be tuck closed so no pressure is releasing out. how does the rod on the w/g look? you may want to take a look to see if the w/g bracket is broke or not. or the actual flapper may be broke...

05-27-2010, 04:17 PM
tested the wastegate actuator and it's good... put air to the line and it clicks every time, actuator looks to be in good shape. is there anything I can look for in vag-com?

05-27-2010, 05:37 PM
So did you see the actuator's rod move when you applied pressure? Are you sure the clicking was from the wastegate itself (inside the turbo)?

In vag-com you can do an "output test". One of the features is that it will actuate the N75 solenoid. It will click it on and off about once per second. If it doesn't click, it could be stuck in the "on" position, where no pressure is sent to the actuator. You could probably even test this WHILE you apply pressure to the N75's boost pressure input. When the N75 actuates on and off, it should cause the wastegate to open and close.

The above "output test" will also test that the wiring between the ECU and N75 is good.

Hope that made sense.

05-28-2010, 05:03 PM
Definitely the wastegate clicking.. sounds more like a clunk actually. It appears to be an intermittent problem because today it was holding boost fine, only spiking to 22psi at most. I'm going to test the N75 when I have some time tomorrow... thanks for all the help.