I had the the intake manifolds/rails etc. off over the winter, got it back together, and with some help was able to get it started. It wouldn’t shift, and after some google searching, I found that I’d neglected to hook up the vacuum hose from the manifold to the modulator on the tranny. Simple fix. It ran fine, took it on the highway and everything was good. The next day, same problem, this time with the hose still connected. I replaced the modulator to no avail. I’ve checked manifold vacuum at the manifold, and it’s at 15". According to what I googled, it should be at least 20". Fluid level’s good. Thinking the problem might be that I’d kinked the hose when I put the manifold and everything back on (vacuum from the hose at the modulator was only 8") I reran the hose making sure it wasn’t kinked. It’s now also at 15". If it’s true what they say, and google never lies, my problem is low manifold vacuum, or is it? Any ideas as to what the problem might be, and to how I might raise manifold vacuum if that’s what it is? (I disconnected all the vacuum advance stuff running the line directly from a connector under the throttle body to the valve off the distributor - the only other lines connected are the three on the back of the left manifold, one of them being the line to the modulator. Any help would be greatly appreciated!
For Paul: It’s a 1988 S3 V12.
And for further clarification, does it start and run better now?
David
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15" Hg is sign of a weakish engine, Ward - but it does not explain the lack of shifting…
Vacuum varies with pedal use, but the vacuum control unit is initially adjusted to ‘tune’ the gearbox to the engine state - as reflected by manifold vacuum…
Since box worked OK initially, and likely with the same engine vacuum - what has changed…?
The box upshifts with high vacuum, like with light throttle - and downshifts as pedal is pressed for acceleration. Lack of vacuum, hose disconnected, blocked or leaking - or a control unit fault; the box will not upshift until very high revs are reached…
You could check manifold vacuum directly at one of the other spigots - to see if vacuum differs. Adjusting vacuum model may be the next step…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Stripped governor gear?
Cheers
DD
It’s running a tad rougher even though the plugs are new.
I’m thinking that this might be the next phase of this adventure
This is the frustrating thing…after connecting the hose that I’d left off, it ran fine. I parked it and the next day the problem reoccurred with the hose connected. Nothing changed. Thanks for the clarification on the vacuum operation re. throttle position/shift points. The other spigots are the same (actually more around 12"…I was just out rechecking all of them). I’ll try to adjust the modulator before trying to tear into that governor.
A contributing factor, or maybe THE factor that I didn’t mention in my original post is that the tranny has leaked for some time. I added a litre of some Lucas anti leak potion and then eventually 2 more litres of ATF to fill it. Maybe that stuffed gummed things up?
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Oi, Ward - this is not the way to maintain an automatic gearbox! 
While any additive (specifically what additive!) is of dubious merit; did you actually measure fluid level. Gear box hot engine idling; passing lever through all positions - then with the engine idling; measure level. then adjust level as required…
Whatever the effect of additives; wrong fluid level will interfere with box operation - and may cause damage…
As an aside; the ‘leak’ may be caused by a defective/leaking vacuum control module - sucking fluid from the box to be burnt in the engine…
Like all vacuum devises; the control unit should be air tight - sucking on the connection (ugh) should show no leak…
Frank
xj6 85 Sov Europe (UK/NZ)
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The tranny leak has been ongoing for 2-3 years now. I kept a close eye on the level (as you described) for that time and topped up accordingly. I’ve never been able to find the exact spot of the leak and was planning on attempting a rebuild this fall/winter. Might be attempting this sooner than I thought!
Symptomatic of worn rings?
I had a look underneath to see what would be involved to get at that governor. It looks like it’s no fun at all. I went on the forums and found a suggestion to disconnect the kickdown switch when I searched under “governor removal”. It worked! I’d noticed that the switch itself (along with the fuel enrichment switch) were broken in pieces when I started disconnecting things last winter, so I installed new ones. Thanks to all who offered their suggestions.
its highly likely its the “transmission shifter seal”
you can tell by cleaning the area directly below the seal to spotless, and check almost straight away for a red trail
unsure what trans you have, but often means the trans needs removal, as the shifter mechanism needs to come out the side of the trans, valve body etc
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A dry and wet compression test is called for, Ward - it will reveal general state of engine wear, or whatever may cause low vacuum. Which may also be caused by other factors - like ignition timing…
However, with no visible external leaks; the automatic’s fluid may be consumed through a faulty vacuum control unit. Which in turn may cause the shifting malfunctions…
Frank
xj6 85 Sov Europe (UK/NZ)
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This is a way out idea, but better than frank’s "ugh’ test. Been there done that, ditto. Not on a trans?? Siphon fuel!!!
Ward. If you do not have one, get one. I have a simple one from HJF. Mitty Vac !!!
1.Put it on the engine end of the hose. Pump up a vacuum. see if it holds. Leak somewhere ???
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Wilder. Use the little pump to create about 20 #'s. on that hose in lieu of the engine. Drive the car release to simulate “pedal”. shift??? Try a few sequences. will it work? No idea, It just might.
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Does the brake booster work. Unless you have Teves, this might be an indication if engine vac is just too wimpy.
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there are after market pumps to assure vacuum on engines with “hot cam shafts” that produce low vacuum, unless revved up really good… Better than a rebuild of the V12??
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As mentioned. compression test. Low numbers there translate to weak vacuum…
Carl .