“I need a new wastegate actuator, my cars not getting positive boost pressure!”
Thats a statement when we hear, we know is 100% wrong. Way too often we hear that statement, and people think their wastegate is not working correctly and so they need a new one.
To explain why, lets go into detail on the way the wastegate actuator works.
Ok, so here is a Neon SRT4 turbofold with the top heat shield missing. We have a yellow arrow pointing to the wastegate actuator, and a red rod pointing to the wastegate flap.
So lets do a run down of the operation of the wastegate with an example of you driving in second gear as boost builds up when you stomp the gas.
– 15 psi of vacuum the wastegate is closed, and pulling on the wastegate flap to keep it closed.
Yyour now at 0 psi, the wastegate is still closed, and pulling on the wastegate flap to keep it closed. Boost is building fast.
5 psi. The wastegate is starting to open the wastegate flap, allowing some exhaust to bypass the turbocharger.
10 psi, boost is still building and the wastegate actuator is pushing the wastegate flap open more.
12-13 psi has been reached, and the wastegate flap will be opening and closing now to regulate boost pressure to the desired 12-13 psi.
So, because the wastegate regulates boost pressure, and its always pulling on the flap, if for some reason it failed, the boost pressure would be very high as it will not be regulating the peak pressure. You would never have zero psi or less with a failed wastegate actuator, you’d have 5-10, 20 psi OVER what it should be.