Decisions about the future of the V-12 in my XJ12C

My 1975 XJ12C is still running pretty well with the original ignition (still points and condenser) and the original D-Jetronic fuel injection. It is running rich and tends to die until it is warmed up. I have yet to do a compression test and oil pressure test with an analog mechanical gauge to determine the overall heath of the powerplant before I spend a ton on getting it to run better. I have done some research on this forum about the option of upgrading the EFI to a MegaSquirt system and feel this may be a viable option given the lack of available electronic spare parts. Just how much of the install and tuning of this system requires a degree in mechanical and electronic engineering? Is the a single source that can walk me through the process step by step? I have some automotive knowledge but I am lost when it comes to fuel mapping and optimum advance curves. If I decide to move forward with this upgrade I would also convert to a Coil on Plug system of some sort as well. I really like to look of the late model V-12’s with the center valley cover. Makes the engine look like a modern car and cleans things up considerably.

Converting to MegaSquirt is something I’ve been thinking about, mostly in preparation for when something bad happens to the Zytek ECU in my XJR-S. I spent some time scanning the, and recently posted a tentative opening question. I get the feeling that MegaSquirt is a known quantity for 4-6-8 cylinder applications, and there seem to be companies that have off the shelf components, but there doesn’t seem to be very much experience of use with V12s.

I think a lot of the installation for a V12 will be very similar to the other configurations, just more injectors and more coil on plug units to wire up. One unknown will be getting a crank position sensor set up made for the V12 front pulley, and it may be necessary to use 2x 6 cylinder driver modules - I didn’t get much further than that in my investigations.


Thanks for your input. I am very much in the same position as you with the ECU in my XJ12C and have surmised much the same from reading numerous posts. I was hoping someone with first hand experience installing the system would offer some guidance.

There are ready to fit solutions as well. @Mobeck in Norway has developed one.

Have you tried searching the Jag-Lovers archives for “Megasquirt”? I have no interest in it myself but I have seen it mentioned from time to time by people who have installed it.


I have never seen a point setup on a Jaguar V12. Can you share a picture? Also, there is a overall mixture adjustment on the MAP canister. This might help your running rich condition unless the diaphram is broken which will cause it to run real rich, hot or cold.

1 Like


Yes I have searched “MegaSquirt” many times. I see the discussion wandering around the subject but I cannot find a complete how-to post by anyone who has actually installed the system. I am wondering how much fabrication and parts sourcing would need to be done to make the system work.


My mistake, there are no points, but it is the original distributor with the weird pickup and injector timing thingy.

I can’t help with info about MegaSquirt installation as I know nothing about it. Perhaps if you created a new post with MegaSquirt in the subject line with your questions and posted it on the Jag-Lovers list where you saw posts about it that might help. You could also try sending a Private Messages (PM) to those that have posted about MegaSquirt and see if they respond.



There’s a regular contributor on the V-12 engine thread called Marek who has what sounds to be a ‘top drawer’ MS set up on his E-Type.

I’ve pretty much never seen a ‘How to’ post on any of the JL forums as far as MegaSquirt or MegaJolt are concerned. I think it boils down to financials: for a long time V12 XJS & saloons have been worth very little money wise - certainly not worth investing £700 in the MS3 & that’s before building the kit, never mind having 36-1 trigger wheels machined to fit crankshaft dampers, creating brackets to mount VR sensors, modifying wiring harnesses etc etc & that’s before you start programming the MS - if you can find someone to share with you a relevant base fueling map for your particular V12 engine variant.

Unless a V12 owner’s background is in electronics, then MS is going to be quite a costly project in my opinion.



1 Like

I think there is poster phillip lochner who did his v12. I did a forum search, and saw phillip had several posts and even had a list of do and don’t. and as Paul Novak suggested you might try to pm the posters

I agree, and I see it reiterated in posts on the MegaSquirt forums for any installation that has not been thoroughly tested and debugged by others with a similar engine configuration. You are pretty much on your own, with a steep learning curve.

For myself, the cost of the physical bits and the labour for the basic install of a MegaSquirt system is probably about the same as ripping out my (what will then be broken) Zytec ECU and replacing it with a Lucus/Marelli set up. And it would be sub-optimal, as I have no easy way of setting up the ECU for the different characteristics of the TWR 6.0L engine, and the modified exhaust I have. I really wouldn’t mind the challenge of getting it all working, but I don’t have a compelling reason right now to invest the time when there are other things that are much closer to breaking, and need replacement.

Phillip Lochner did the dual EDIS distributorless ignition conversion on his XJS. I think Phillip’s MS conversion was on his E-Type.

I liked the idea of the Nippon Denso distributorless ignition from the end of line XJ12s & Double Sixes (X305 or X308?) being retrofitted to my XJS. That system has a cam position sensor (sequential injection?), different camshaft & different cam cover on one bank - Marek dissuaded me with 2 words: mission creep.


I’ve no affiliation to the seller but this has been recently re-listed on UK eBay & it doesn’t look overly expensive to me for the Zytec equipped XJR-S owner to have as a spare considering the rarity of those Zytec distributor pickups.


Oh great, another variation to consider for timing - crank pulley (I saw there was a Pontiac, or Ford Taurus, with a 36-1 tooth wheel that would fit a Marelli damper), distributor trigger from my modified Lucas distributor, and now a camshaft sensor option. I already have sequential injection, but would probably need to change the injectors to handle saturated coil mode (apparently).

Yes, it’s a lot of work, even when there are some Jaguar retrofit parts available.

If you have local support MS is OK but if there is no local support then it is a nightmare. The documentation is horrific and the MS Forum treats newbies with little knowledge as lepers.

By pass a MS and go a built and ready to go system such as Adaptronic M6000 ECU.

8 posts were split to a new topic: Mobeck V12 engine management conversion

5 posts were merged into an existing topic: Mobeck V12 engine management conversion