I believe I understand the basis of a valet switch...cut off the boost (generated by fuel) to the injector pump, and hence...no boost, and no power. Ok, a little simplified.

Question I have...if I cut off the boost to the injector pump (valet switch), and therefore do not utilize the potential of fuel the injector pump is capable of delivering...won't this increase my fuel mileage? I am basically asking...will a valet switch improve fuel mileage?

 

The more I think about it...power in the CTD is like a snowball effect...fuel produces boost, which moves the lever arm, which injects more fuel, producing more boost, moving the lever arm further up the plate, and therefore producing more boost...until rpm max is reached and/or wastegate opens.

Therefore, the valet switch HAS to improve fuel mileage...right???

 

If anything I get a little worse milage with it on, but it really is a wash.

 

I smoke waaaaay less with it engaged. I would think that'd be better for mileage, but only taking into account pre-spool fueling. So if you're driving mostly in-town, should help.

I put it on as assurance for the smog test.