Hello, all! As with many XJ owners my car ('88 Canadian-market V12 VDP) is likely suffering one or more vacuum leaks due to aged rubber lines falling apart, and I have a few that seat very loosely on their respective connections at the intake manifolds/other devices. I would like to re-plumb all these lines, but unfortunately much to my dismay my car doesn't seem to have any vacuum diagrams under the hood. I've searched high and low on the forum and other Jaguar enthusiast sites, and have found plenty of diagrams for the six-cylinder cars and a few for the older V12s, and I have a Series III Service Manual (ca. 1985, unfortunately...) and the Haynes manual for XJ12s and XJ-Ses, but none of the diagrams I've found match what's in my car as it sits. I would rather not begin replacing the lines by tracing what's connected now, as I don't think it's correct anyway; I have a pair of delay valves (one red/black, one grey/black, plumbed one after the other) that the previous owner included loose with some other spare parts which he freely admitted he wasn't sure what they were for and where they were supposed to go. As such I'm not confident he knew how to put it all back together...

I found a bevy of XJ-S diagrams on Sean Straw's website (http://jaguar.professional.org/vacuum/), but none of those match either. And the fact that these were all from photographs or scans of decals under-hood makes me wonder: surely the XJ12s came with similar stickers somewhere in the engine bay, no? Do any other late (post-'87 ) Series III V12 owners have vacuum diagrams under the bonnet?

 

I hope someone can help. I can't, sorry.

Information on the later Series III V12s is very scarce. XJS info is often helpful....to a point. As you note, there are differences.

Sometimes the parts catalog illustrations are helpful in sorting out vacuum hoses. The illustrations are often detailed enough to be useful, but not always. Might be worth some perusing:

https://parts.jaguarlandroverclassic.../brand/jaguar/

The matter is complicated by different year and market configurations...which confounds XJS owners as well, I might add.

Since the later Series III V12s were low production models I suspect a lot of tech info was published by Jaguar in the form of "Supplemental Manuals" and Technical Service Bulletins. That info is probably out there "somewhere". Over the years I've done some searching....on-and-off as my mood and inspiration dictate....but always come up empty-handed.

Sorry I can't provide something useful for you.

Cheers
DD

 

Appreciate the reply anyway Doug, even if you don't have more detailed info. Given how many times your name popped up in related searches I suspected you'd be one of the better resources on the forum, and I contemplated sending you a private message directly.

It's tough trying to piece these various diagrams together, and such a shame that something comprehensive was seemingly never published at the time. Crazy to me that it wasn't. I've poked my head under the hoods of '80s Hondas with an even greater myriad of vacuum lines than the V12, and despite the complexity of it all Honda sought fit to put a VERY complete decal under the hood. It seemed daunting at first but it showed everything. Made it much easier to follow along.

Instead, even the information in the Jaguar-published service manual is piecemeal, requiring the reader to flip between the fuel system and emissions control system sections, and even then it's not quite right. Hell, none of the diagrams in the service manual even include the damned vacuum regulator!

 

Same as Doug.

All the V12's I have had have been different to each other, and the diagrams have always been vague at best.

The HE cars were bits of Euro/USA/UK/ROW, and that really was frustrating.

Remember, we got almost zero emissions stuff until about 1989, and even then it was state dependent.

I 1st replaced the vac hoses ONE at a time, almost the first week of ownership.

I worked fo Jaguar at the time, and even inside information was less than I had in the flesh.

Eventually de-smogged them all, as no testing ever, and that sorted so many running issues in one foul swoop.

 

Hi - again not what you want but maybe some help in general. Would be nice if V12 was just this x2... but I know that is not true

But I recently replaced all of my ‘86 SIII US vac lines and put together this pix from all the stickers and parts manuals etc

Good luck!!

Randy

 

try contacting the Jaguar Daimler Heritage Trust ( www.jdht.com ) since they have a library of documents all the way back to 1933.

 

Thanks Randy, I saw your post in Sarc's old thread "Vacuum line replacement pics :: In glorious technicolour". I think I'll end up putting together a similar sketch for my sanity's sake.