So what is this vac component
 

The block on my 2000 1500 5.2 rusted out and, I blew a head gasket so I bought a wrecking yard motor that I put a new timing set in, rod bearings and oil pump. I just noticed this component on the wrecking yard motor that my original motor does not have on it. What is it, do I need it to pass CA smog?

thanks!
https://cimg6.ibsrv.net/gimg/dodgefo...d56515a2b5.jpg

Purge solenoid. On later engines it's mounted to the passenger fender.

Thanks for the info! What years would have had it mounted in this location on the rear drivers side of the head. I ask because the old harness that came on the wrecking yard engine would not work with my chassis. Instead, I used my harness and had to swap over all the injectors/sensors/senders from the old engine to the wrecking yard engine in order to get the harness to hook up correctly.

I'm not sure where it was mounted or if it was even used on older engines. It may have been stuck there from the crew that removed the engine because that location would be tight under the firewall if factory. But the engine also has the pre-98 vent on the valve cover.

I've only seen them on the fender under the intake tube. It probably doesn't matter where you mount it, but on the engine is weird.

And you'll need a rubber tube from the red cap to the airbox when fitted.