Jaguar V12 Vacuum Advance Delay - safe removal

How to safely remove the vacuum advance delay from your XJ12 / Daimler Double Six / XJ-S V12 HE engine. This improves engine efficiency during the first 15 minutes of car use (though slowing engine heat-up slightly). No noticeable effects to engine behaviour and removes clutter from engine bay.
(Note: this modification was performed on an HE engine that does not have the air injection system)
Living with a Classic: / @livingwithaclassic
Kirby Palm V12 technical guide: www.jag-lovers....

[@workshop_deluxe2493]

Thank you so much for this brilliant video. My H.E. had serious idling issues, making me mad . Shutting off this circuit made the XJ-S and me happy again. Greetings from Germany.

[@cosgraham534]

I'm delighted to hear that! Thanks for the feedback.

[@LivingWithAClassic]

Great video! That looks like a beautiful Daimler. Thanks again for the mention

[@simonray2302]

Just want to say a big thank you . I have been working on my 1985 XJSC renewing the injection rail hoses and tip filters , replacing the inlet manifold gaskets. When putting all the vacuum air system back it was a nightmare. I followed your instructions and did away with some of the relays, valves and rubber hoses ,and reconnect as per your Video ,she runs like a dream and so much simpler .I also live in Australia on the west coast so we don’t suffer the cold weather so she should be fine . Once again thanks .

[@cosgraham534]

Thank you for your message - that's great news about your Jag! Happy driving.

[@jsquared1013]

6:00 *Star Spangled Banner intensifies* 😂 (Yes, I know you're Down Under, but I feel like it's almost an obligatory tradition for some of us 😆) Anyhow, thanks for pointing out the "try it before you buy it" trick at 8:55. I'm doing some "catch-up maintenance" on the XJ-S that I recently acquired, and I'll add this to the checklist while I'm refreshing the fuel lines, vacuum system, and the like. It seems to me that the 15-min vac delay system is more emissions-focused than anything else (e.g. run warm to get the cats heated), but I do need to dig into "The Book" a bit deeper than my initial skim. Cheers 👍

[@cosgraham534]

Good luck with the work you do on your XJ-S. BTW, it was a .223 Remington case at the 6 min mark - you are the only person to notice!

[@ahmadalraies6948]

Thank you for the wonderful video. I actually do not like to fix things by canceling other things, but it seems that we must do that in the 12-cylinder Jaguar. I replaced everything that could be replaced and did not reach any results. The car barely started with difficulty, and now that I connected it according to your video, it ran. Things are going well, but my question is, does this affect the engine in the long run and fuel consumption? Thank you again

[@cosgraham534]

I’m very pleased to hear the good news - thank you for sharing it. The purpose of the vacuum delay advance is to make the engine run inefficiently from cold, so the engine heats more quickly. Have a read of the Kirby Palm book pages 133-137 for a detailed explanation of this. This modification will allow better fuel economy from cold, via a less fuel-rich mixture. This will decrease wear inside the 12 cylinders burning fuel. But… the engine will take a little longer to get to operating temperature. As these cars are now classics that are used occasionally and are treated with respect and are (hopefully) well maintained, any such effects are negligible. Just make sure you always run your car up to operating temperature whenever you start it (decreases spark plug wear and engine wear due to water condensation on engine components).

[@peteraves581]

Thanks for the video, Cos....and I might be your first subscriber! I have removed the complex vacuum advance system on my 86 V12 too -mostly because the vacuum modulator stopped working correctly and I couldn't find another. I'll put the dump valve back into the system now, though. One thing to add, I believe the Extra Air Valve (EAV) also provides extra air when when the car is in Drive/Reverse and AC is switched on,..... to prevent revs dipping too low. It also keeps revs a little higher during cold start. I found you can remove the switch that closes the vacuum to the advance but keep the EAV working - which is what I've done.

[@cosgraham534]

Thanks Peter - I have been enjoying your videos too - you have inspired me to attempt a radiator upgrade myself. I'm going for an aluminium rad with twin electric fans. The mod you suggest for the EAV sounds compelling - I'll see how my car goes over the next few months (Summer and Winter) and will implement it if I have any low-idle issues. Thanks for subscribing.

[@carlitox3113]

Nice mention to Kirby Palm´s "The Book" in the video. That shows true knowledge!

[@boyfromblackstuff7859]

Very interesting,my own XJS can be quite erratic on starting in cold weather,I wonder if this is part of the issue? Thanks for posting.

[@cosgraham534]

I would look at the coolant temp sensor on the left side of the engine (as viewed from driving position). It’s near the front of the engine - a poor connection and / or failing sensor, will have your engine hesitant when cold. The problem is worse the colder the engine and decreases as the car warms - the fault is telling the ecu the engine is hot, which leans the mixture (when a richer mixture is needed). You can test it by disconnecting the sensor and starting the car from cold and attempt a drive - if there isn’t much difference in performance, that is the problem. Let me know how you go.

[@boyfromblackstuff7859]

@@cosgraham534 thank you for your reply. Have replaced all coolant temperature sensors and thermostats with new original Jaguar items , wiring check is next on the fault finding list,time permitting. I have found your videos most informative. Many thanks.

[@cosgraham534]

@@boyfromblackstuff7859 Thank you for your comments and good luck with your car!

[@thomaspetersen2642]

Brilliant video, thank you so much. Don`t underestimate the value of sharing such experience and information with others.

[@cosgraham534]

Thank you for your kind words - I really appreciate the feedback!

[@stevejelly3161]

Hi Coz !!! .... It must be a beautiful car to own ??? .... I learned years ago that there were never any "plans" for that engine from it's launch in 1970 !! .... ( i'd guess the vacuum delay retards the engine until it's warmed up ?? ) .... Your car is like a "marque" of engineering with a very sedate street presence !!! .... Coz i'm afraid i cannot see ONE virtue in a new car whatsoever !!! .... The interiors are like "designer kitchens" , The tires cost about £150 each , Those interactive screens are "putrid" , The fuel economy only just exceeds your car, The seats look like they've been bought in a computer shop , The paint fades quick , They look outdated after a few years , And last but not least , continual "road noise" !!!

[@padge4691]

Excellent research Cos. I plan to do the same on my '83 XJ-S as soon as I've had the vacuum advance module repaired. One question: why did you find it necessary to fit the inline one-way vacuum valve into the feed to the dump valve? It was my understanding that the function of the dump valve was that of a one-way valve, but with the added function (to dump vacuum), controlled from it's connection to the inlet manifold. Thanks.

[@cosgraham534]

You may well be right on your suggestion - it sounds logical. It is a long time since I experimented with my car and got a successful outcome. My car is performing perfectly now, so I won't make any further changes. Relating to vacuum advance... make sure to lubricate the advance mechanism in your distributor, and seal the connections in the vacuum lines - all the way to the inlet manifold. Good luck!

[@jeffball6108]

@@cosgraham534 Its not a one-way valve, it's actually a restrictor which has the effect of delaying the vacuum. To be honest, I cannot fathom how this setup actually provides better fuel consumption. In theory it shouldn't.

[@nickhoare6616]

Great video, thanks for posting. Going through all this now on my ‘86 Cab. Unfortunately today found the vac advance diaphragm is stuffed so now to find a new one somewhere.

[@asdreww]

Hi, is this applicable to the 1988 onwards HE with the Marelli ignition system?

[@cosgraham534]

My understanding is the Marelli distributor does not feature a vacuum (or centrifugal) advance, so this modification does not apply. Good luck.

[@JAYPCARS]

Great, looking forward to giving this a go!

[@chasermalloy7406]

You limit revs to 4000 ? You're missing all the enjoyment. You can't kill these things if you try. As long as you don't ever let them cook they'll never break. BTW, as you'd realize, there are several different setups in this area in the various markets, but people should be able to identify the components and work their way through this process allowing for different vacuum hose setups etc.

[@cosgraham534]

Hi Chaser - I have revised my approach to revs on my V12 since I posted that video. Having worked on the ignition system and vacuum system, and installed K&N air filters, the engine response and power have improved noticeably. I am now a lot more inclined to exercise the revs… What an engine! If you spend long at high revs, bear in mind the standard water pump is geared quite highly - race-tuned V12s gear down the pump by about 30% to stop the water cavitating at high revs. You make a good point about the different vacuum setups for varying regions - the Haynes manual gives the schematics for Japan, US, UK and Australia. I thiiink my solution is ‘agnostic’ to the various regional setups, since I am removing the factory components and creating a generic one. I cannot guarantee that and probably should have been clear about it in the description.

[@chasermalloy7406]

@@cosgraham534 Yes, but I think your video adequately describes and identifies the components well enough that anyone liable to be doing it will have no trouble. And yes, the engines are still without parallel in strength. With forged chrome molly cranks and rods and such large dimension of bearings and lower crankcase. Add that to the much lower load per member of a V12 engine and you understand why a V8 would struggle to compete in ultimate terms. Keep the cooling system and hoses as well as the injection hoses etc in good shape and the things will go forever. I remember the first one I pulled down in 1983. It was a 1974 carbureted XJ12 with over 100,000 miles and the crankshaft was still on standard dimension - mains and big ends - no ovality, no scoring - no nothing.

[@cosgraham534]

So nitriding the crankshaft really works...

[@chasermalloy7406]

@@cosgraham534 Yes, I'm sure it has the stated benefits. The V12 cranks are actually tuftrided and that's why Jaguar stated that the cranks need to be returned to them to be ground. I assume that's because tuftriding does not produce as deep a hardened casing as nitriding. A 20 thou under grind would effectively remove the tuftriding. I'm sure that the process could be managed by the right company anywhere these days if needed.

[@andrewk8656]

Great video very well produced and easy to follow. Has helped me out considerably in my effort to tidy up the engine bay in my series 3 sovereign v12, I am also in Aust so engine warm up is not too much of an issue. It would be great to see any other modifications you have implemented on the car.

[@cosgraham534]

Andrew K Thanks Andrew, I’m very glad it helped. I plan to upgrade the cooling system at some point, and I’ll post a video of that, when it happens. Cheers, Caspar

[@schaebse]

Great Video. Did I understand right: If I try to remove one cable from the water heat sensor I have the same result ? How do I recognize an airinjection system. I drive a 92 DD6 here in Germany. Thanks !

[@cosgraham534]

That is correct - you can disconnect one wire from the coolant temperature sensor and the vacuum advance delay system will be disabled. I am sorry but I cannot help with the air injection system. It was not fitted to my UK car. I would remove the system entirely!

[@schaebse]

@@cosgraham534 Cheers mate ! The air system is in the american cars to blow fresh air in the exhaust to fulfill enviorment messures

[@thomaspetersen2642]

Just tried this but is experiencing higher idle rev. Have others had the same result?

[@cosgraham534]

Have you blocked the spare vacuum ports that are no longer used - specially the extra air valve port?

[@thomaspetersen2642]

Hi Caspar. Yes I have. All unnecessary ports are blocked by means of a short piece of hose with a metal stud in it. Just as you've blanked off yours. If you haven't noticed any change in idle speed then it's obviously something to do with my car. Only thing I can think of is the dump valve, as I tested the one-way valve to ensure correct vacuum flow through it. All good, I'll do a bit more investigation. @@cosgraham534

[@cosgraham534]

@@thomaspetersen2642 Ok, good luck with it. Can you please let us know the source of the idle speed issue when you have resolved it, I’m intrigued?!

[@marksbikeexports5123]

#7 is NOT a check valve, its a vacuum delay valve, 'Standard motor products vacuum delay valve DSV9' to be precise

[@cosgraham534]

Can you please tell me its purpose and mode of operation?

[@cosgraham534]

I don’t think I used the term ‘check valve’ in the video - I referred to it as a ‘one way valve’, which is how it works in my set-up. It allows vacuum to only work in one direction. This configuration is of my own (trial and error) design, and I have repurposed that ‘DSV9’ component to control the draw of vacuum.

[@joeking469]

I have a question about a hose. Do you know where all the vacuum hoses go from one to another? If yes, how can I contact you?

[@cosgraham534]

Hi - I can certainly answer questions on how I have routed the vacuum lines on my car. Why not post a question on the 'Real XJ' Forum, of which I am an administrator: facebook.com/groups/925138951319777

[@lebojay]

Thanks for this!!

[@9danny81]

Hi, thank you very much for this video! It is greatly appreciated as I've been scratching my head over the routing of these vacuum lines since I got my XJ12. In my car, the vacuum lines from the dump valve are in a loop not connected to anything else. Several other valves in the circuit are disconnected and it's just one big mess of confusion. Can't wait to try out this setup. Thank you again!

[@cosgraham534]

Daniel Great, I hope it all works out for you. Please let me know how it went!

[@9danny81]

@@cosgraham534 Came back to report and thank you again as the operation was a success! Threw out all that junk, started her up and for the first time since getting the car, it actually idles and holds rpm, so I'm very excited. Although the idle RPMs are stable now, it drops a bit every now and then, so I still have to sort that out. And a bunch of other stuff, but when are you ever really done with these cars.

[@cosgraham534]

Daniel That is excellent news! I’m glad it was a success - thanks for reporting back. For the other issues such as the misfire, I recommend you try searching the Jag-Lovers’ forum for answers: forums.jag-lovers.com You need to join the forum and then you can search for key words eg ‘misfire’, adding #xj, and you can search through lots of helpful info. It is an invaluable resource that has helped me diagnose and fix multiple issues with my car. Best of luck!

[@cosgraham534]

Daniel - you may be interested in the following XJ-specific Facebook group: facebook.com/groups/925138951319777/?ref=share

[@bixkauldhar1566]

BL have a lot to answer

[@cosgraham534]

Points for effort - just poorly executed

[@spartanreaper911]

is their anything like this on the US spec HE engines? ill be removing my air pump system in a few weeks here

[@cosgraham534]

If you are able to remove your air injection system, and you can get your engine running correctly without it, you should then be able to follow my method to remove the vacuum advance delay (VAD) system and get the same results as I have. If you disconnect the coolant temp sensor (as shown in my video) you will disable the VAD on a temporary basis, to see how your car responds without it e.g. how much slower the warm-up is, and what sort of improvement in fuel economy you get. If you are happy then to proceed, I cannot think of a reason why removal of the system would not be successful. You will have effectively converted your V12 to a 'standard' spec, by removing the North American spec components and configuration. If you want to be extra cautious, you could always keep the existing VAD system components in place, and then rig the system up like I have done, borrowing the existing pipework, re-plumbed into the new configuration (remembering to block off ports and pipes that have been opened to atmosphere). Let us know how you get on!

[@bobjason]

Hi Gavin, I have the same Jaguar as you a US spec 1990 XJS, did you remove your air pump and if you did, did you have any luck with Grahams vacuum delete process, I'm looking to do the same? thanks

[@spartanreaper911]

@@bobjason so regarding my first comment forever ago, since then I have removed all the vacuum lines and even the intake manifolds and injection system, I’m converting to carbs so their isn’t much info I have on the injection vacuum system lol

[@bobjason]

@@spartanreaper911 Thanks Gavin for your reply and good luck with your on going project.

[@mcashnv]

brilliant solution

[@cosgraham534]

Thanks - I have spent time recently, sealing the vacuum pipe joints and lubricated the vacuum advance mechanism in the distributor. That, with new HT leads / cap / rotor arm and plugs, has further improved the response and smooth running / acceleration of the engine.