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This fix is for 5.3L HE V12s that predates check engine lights. What year / version car do you have?

@ 1992 5.3l

This, actually, should go into "The Book" as a best practice

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.

@@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.

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

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!

Lots of different ways to approach it - whatever gets the results you want, eh?

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Thanks Jeff. I have just taken my DD6 out on the first ‘proper’ run in warm weather. The new fan setup is very effective - a big relief. Good luck with your change to a V12.

Hello - I did not install the windscreen, it was done by a professional. I know the series 2 are glued in - there is a video on the topic in youtube channel ‘living with a classic’. I do not know if series 3 (like mine) are bonded - I imagine they must be!

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).

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

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

@@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?!

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

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

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

Hello Mustafa - in which part of the world are you based?

@@cosgraham534 Hi Cos, I'm located in Hoppers Crossing , Vic 3029

Ok, thanks. A couple of points - the guy who sorted my screens did not want me to name his business, because he works on his own and gets sufficient work from referrals via Spiteri’s and Mike Roddy. He really is the only person in Melbourne who knows XJs for bodywork. If the rust around the screens needs welding, you will need to get the dash and headlining out at the front, and the petrol tanks out at the rear (I guess you could fill them with water instead). That is all very labour intensive. I can probably get the contact details of the bloke who knows how to remove and replace the screens - he did mine and provided the rubbers.

@@cosgraham534 Thanks Cos, i will find someone to see have a really good look to see if it will need welding. thank you so much. Will be in contact.

@@mustafabala1001 I will do what I can to help.

Hello Peter - can you please advise where you are based? Regards, Caspar

@@cosgraham534 Thanks for your reply; I’m just outside Newcastle in England.

@@petermyers5793 My location in Melbourne, Australia, is probably not going to be of much use to you then!

@@cosgraham534 Maybe not, or maybe. My problem is figuring out how the seals are “sandwiched” into position. It seems that the thicker seal goes to the underside of the screen, then the thinner type seal (which has a groove on one side of it) goes to the top side. Figuring out where to position the sides with the grooves in them has me unsure. Maybe I’ll consult with the JEC over here. Maybe they know a professional who regularly does these. All series 3’s rot like hell over here so it has to be an issue that’s been addressed my many owners.

@@petermyers5793 I’m sorry I cannot help - this advice is for a S2, but may be of use? th-cam.com/video/6WNmFrpM4Rw/w-d-xo.html

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

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.

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!

@@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.

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.

@@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.

So nitriding the crankshaft really works...

@@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.

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!

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

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

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

Hi Trevor - My car is a UK import, so has that configuration. You are correct to point out that the Australian config is different (as are US and Japan...)

Points for effort - just poorly executed

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.

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

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

@@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.

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!

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

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!

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

@@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

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

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.