XJ12, year 1992 vacuum diagram

XJ
1

Guys,

my mechanic is finishing restoration of my XJ12, series III, year 1992 engine. Now it seems he has some problems with engine vacuum adjustment (hope I got it right…).

So - is there any “vacuum diagram” for that V12 engine available. In my green Service Manual book I cannot find anything that would help…

Thank you in advance for any help or suggestion,

Cene

2

Vacuum set-up depends on witch market the car was ment for.

This is for the North American market (1986)

Vacuum Routeing Diagram 01

vacuum_01
vacuum_01703×619 76.8 KB

Also if your XJ12 is a very late SIII you are at the right place.
If it’s a XJ40 you should ask on the XJ40 forum.

There is no such thing as Vacuum adjustment… maybe he meant the vacuum advance set-up?

3

Hi, Aristides! Helpful, as allways… :smiley:

yes - I know, now about “adjustment” - he put an engine out last year… and of course he did not take a photos or made a memo how the tubes are positioned…

I hope your set-up will help - as I have read somewhere, in the last years of production there was no unified approach that one can rely to…

Will send him your diagrams, and see what he will say.

Thanks again for your kindness,

Cene

4

You are welcome Cene.

Here is some more helpful info about the rather complicated vacuum advance setup.
A thing that I and many others have done to somewhat simplify the system, was to delete the solenoid that kills the advance for 45sec once you start the engine.
Others have gone more extreme and just connected the vacuum advance directly at a ported vacuum, others at full vacuum.

Much more info at Kirberts Book.

Vacuum Ignition Advance.pdf (186.9 KB)

5

Great, thank you, Aristides! Will check it and forward it to the mechanic.

Best, Cene

6

best way I found to to get your vacuum sorted out and routed correctly was to have another XJ or XJS that’s not been played with for comparison.

7

Mike, true - but I guess in the last years of production not all cars were exactly the same… mine is 1992 - there is another V12 at my mechanic, year 1988 currently - and mechanic said it does not help much… Also - in my country there are probably one or two of such cars beside those two, anyway… :slight_smile:

Cheers, Cene

8

To be expected, Cene - the vacuum diagrams for ign advance varied with market according to emission control regulations, which also varied over the years. Other vacuum lines varied with equipment level, with variations in routing - which is rather immaterial; the point is to get vacuum to where it is needed any which way…

Frank
xj6 85 Sov Europe (UK/NZ)

9

Yeah, Frank, exactly… I guess mechanic will have to do a lot of trying and testing…hope he will learn to make few photos when dismantling things in the future… :slight_smile: Hope he will finish it soon… waiting for my Jag to be back for half a year now… damn. :slight_smile:

Cene

10

Tell us what he doesn’t know how to connect and we might be able to help.

11

Thanks, Aristides… it might well be that he will do it right when he starts… he is just complaining for now… :slight_smile: but in order to speed up the process I tried to get as much info and help before that.

I will for sure again ask for help from you, guys, when and if he will have concrete questions.

Best,

Cene

12

**
Generally the V12 will run with ‘conventional’ vacuum advance set-up, Cene, but it may misbehave at some rpms and load ranges if the sophisticated set-up is misconnected or with faulty parts…

Trial and error may not be an easy task…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

13

yeah, I see that…I think I will just let the mechanic try to put all back and see the result…and then I will be back with you, guys - if there are some problems…:slight_smile:

Thanks, Cene