I'm wondering how I could test the VDI system on my motor to see if it is actually working. This is because this is a swapped S5 longblock in my S4 gxl. I can't really do a butt dyno test since I've never been sure the VDI is working for a reference point. What I can say is that the car seems to run out of breath up in the higher rpms. I'm pretty sure my aux ports are working since my airpump is hooked up. Any input would be appreciated.

 

actuate them manually,

 

connect a vacuum tee to the line running to the actuator diaphragm and check to see if it's getting pressure

 

Couldn't you have someone check the actuators during the dyno test? Anyway the S5 actuators actually push out of the maniflod so the good old grease trick wont work. Try tapping a hair to the actuator and manifold, if the hair is snapped after a short drive then the VDI should be working. I you don't like my idea then just use some imagination.