A long while back there was a discussion of the vacuum advance for the cruise control. Some models used an engine vacuum source and others, including my 1992, has a pump that manufactures vacuum.
My car has the pump pictured and the switch, but the rest of the system disappeared when the v12 was replaced by an LS1.
I happened to have an aftermarket Audiovox cruise control system from another project. I would like to use the Jag vacuum pump [assuming it still works] for the Audiovox. The picture shows 2 hose barbs. Which one would go to cruise bellows?
Also for the Audiovox to set the speed correctly I would have to know the pulse rate of the Jag speedometer. Anyone know what that is?

 

That T-piece in the pic would have a hose that goes to the bellows.

See here for the the various parts at the vacuum / dump

Genuine Speed Control Dump Valve-4.0/5.3 Litre (4.0 Litre,5.3 Litre) For Jaguar Xjs Sports Coupe/convertible 1975 - 1996 Classic | Jaguar Land Rover Classic Parts

cheers

Paul

 

I just realized I never replied to you on the other form, my bad. Yes as Paul said, and as the illustration shows they go like that. My cruise still doesn't work properly, but I haven't really looked at it recently. Mine doesn't do anything when I try to set it, but then when I turn my switch back off, LOOK OUT! After a half a second or so the car starts accelerating on it's on and doesn't stop until I hit the brakes. First couple of times it kinda scared me I must admit!

 

Paul... Great link! The Forumi gods must have read my thoughts this morning since C/C in-op was on my mind. My 92/93 4.0 had been "hit and miss" for quite some time. Found a vac hose disconnected (who knows how) and re-connected expecting that to solve the issue. Of course, it didn't. Now I need to diag the rest of the system.1 problem tho is location of the DUMP VALVE. Research says "right front inner fender". Is that under the hood or under the fender well?

thanks, Dave in AZ

 

I'm still a little confused. The very useful illustration [thanks, Paul] shows 2 vacuum lines, both numbered 7. I assume that the vacuum hose from the T [#5] would go to the cruise bellows. If so, what is the other nipple on the speed actuator [#8]?
From the many posts it appears the Jag cruise system can be problematic with age. It also appears to be antiquated technology. Even my Audiovox aftermarket unit is outdated compared to the Rostra units. All I need is for the Jag unit to develop vacuum on demand. May be asking too much though.

 

wufibugs,

I'm pretty sure that nothing is connected to the other port. I thinks it's an outlet port for the vacuum being pulled?

Paul

 

Dave,

It's under the bonnet (hood) on the inner wing (fender), under the black plastic panel.

Paul