I replaced my 1999 XK8 vacuum purge valve (original part number LJB1515AA) with LJB1515BB which supersedes the original LJB1515AA unit. I find that the superseded part has what appears to be a vent that is not part of the original unit. I’ve attached pics of each. My question is, does this vent to the atmosphere? I’ve seen these vents before on my XJS, and it vents to the atmosphere through what looks like a fuel filter.
I swapped mine with an LJG1515BB which has an extra capped off port but not the one yours has.
It may be a vent instead of the one coming out of the bottom so I’d be tempted to attach the tube from that to the top port on the cap. I can’t remember but i think the other unit is either a filter or one way valve
I’m going to attach a tube and a filter to see what happens.