What does VSV do that modulator doesn't?

[kerrye]

No, you have it backward. ON means the valve is closed to stop vacuum from escaping. OFF would be the options you are losing.

Something funky is going on, either in my mind, my system or that chart. I've checked my modulator and monitored the system with the line to the VSV open and with it plugged off. With the line unplugged and the VSV open, there's no vacuum at all in the system so the EGR cannot work. With the line plugged, I get vacuum in the system off idle which I think means the EGR must be working most of the time.

 

[kerrye]

Ok, I see where my confusion lies. With the VCV on, which means it's closed and no vacuum can escape, there is one set of conditions where the modulator itself opens to atmosphere and does not allow the EGR to open. I have not observed that condition when I have had my vacuum gauge T'd into the system. The modulator has always been opening the EGR above idle when I've monitored it.