How does the MK7 control boost?

[mto386]

Can someone intelligently explain how the mk7 controls boost? After using cobb for awhile, I've been trying to diagnose a boost leak or whatever it is I'm having. What I thought was wastegate duty with cobb is actually just wastegate position. N75.. DV... huh?

 

[aaronc7]

If you're familiar with modern turbo systems.... it's very similar except it uses an electronic wastegate actuator vs an electronic solenoid connected to a vacuum/pressure actuated device. Normally 100% WG duty would mean the solenoid is bleeding or keeping positive pressure away from the wastegate actuator in an effort to keep it fully shut, or at least as closed as possible (there's exhaust pressure that could be cracking it open slightly etc).

An electronic wastegate is really just a much more straight forward way to control to wastegate position.

So yes looking at WG position is a good place to start to help ID a boost leak--you would expect to see it more closed or 'working harder' for a given operating point. It's something that is naturally going to vary quite a bit depending on air pressure/temp conditions, but if you datalog often and have a keen eye it can be very helpful to ID issues as they crop up.

Hope that maybe cleared it up some.

 

[Twist1]

Best way is to put a fitting into a PCV cap and put into your turbo inlet pipe. Pressure to 26-28psi with oil cap off and if you CAN its nice to cover pcv hose outlet as well but I used to just leave on without any issues. Then spray connections with water but usually youll hear the leak.

If you have OBD11 or another logger you can look at boost specified vs boost actual and overlay the graphs. If it is struggling to match requested psi up top than yea it's probably a boost leak. Sometimes they're hard to diagnose small leaks because it could be just enough leak that the ECU can compensate by adding more WG to hit targeted boost in manifold but still would never know until it got big enough to really start dumping boost out. WGDC data is worthless without a comparison to be made. (ie logs from when it was working correctly in very similar conditions). But still there's so many variances and calculations these ecus do with boost it's hard to compare and say definitively yeah thats a leak.

For instance when I installed my DBv2 I literally forgot to fully tighten one of my hose clamps and I drove around for 2 days not even realizing a thing. Drove completely fine until the first real pull went up to about 14psi and POP.