I searched but found nothing. . .

So my question is, is there such thing as preloading the wastegate too much that it runs lower boost than it should?

 

if you preload the wastegate to much, you are just making it harder for the gate to open up, so no, to much preload will not cause lower boost. there is the possiblity that you broke something, such as the flapper in the gate itself. also it could be possible you are actually unloading the spring instead of loading it. when preloading a wastegate actuator, you want to make the actuator link shorter. if it has a turnbbuckle, you want to thread the turnbuckle into the link. this will pull the gate closed harder by pulling on the spring more, i.e. preload.