Distributor cap sparking

Hi all,

Any idea why my distributor cap would be sparking when i try to start the car?

The car was in bad shape when i got it and i replaced the distributor cap because it was missing.

Thanks for helping!

Hi Sean, I have moved your post to the XJS forum as your photo depicts a V12 and your profile says XJS
Please advise if this is a different car that you are discussing.


What year and model Jaguar are you asking about?


His info lists this: My Cars: 1986 xjs

And it looks like the V12 speed control bellows and other stuff in the photo.

He posted to the XJ list first and Robin moved it over to the XJ-S list.
Attached is a picture of my 1990 Series III V12 Vanden Plas saloon showing the same components in my XJ12.

Based on the information so far it is hard for me to tell whether he is asking about an XJ-S or XJ12 and what list he should be posting on.


I think he’s asking about his father’s Canadian 1986 XJ12 based on his previous topics.

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Agreed, I just clicked on his icon, which only showed the XJS as his cars

Hi Paul,

Thanks for the reply.

I have an 86 XJ-12. In Canada its the Vanden Plas.


Which may have even confused the moderator to move hus post?

From the photo, it looks like my XJS, however, such a close up view, is there any/much difference between the V12 in either/both of those cars.

If one has more than one Jaguar, yes, always should provide year, model, engine, and other pertinent information (such as if a convertible for XJS, OTS/FHC/DHC, 2+2, etc where applicable).

I doubt I’m the only one to click on the avartar/icon to see what is listed as their car for starters … but it is at times an incorrect presumption to make).

Edit: I was typing as he clarified which car.

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Thanks for the heads up on updating my profile!

I have an 86 XJ-12 Vanden Plas.

The fuel rail, distributor cap and a boat load of wire and vacuum hoses were missing when i got the car.

Ive veen slowly puting it back together and this is the first time i tried to start the car.

There were sigificant sparks in and around the distributor cap and i was hoping to get some insights from this kind and knowledgable board.

Thanks again,

I am one of the least knowledgeable ones here, but is the cap fitting on the distributor correctly? Starting at a basic level.

Sparks down in ‘The Valley of Death’ is just outright asking for trouble. Which is usually followed with the word “FIRE!!!” and then a race to get the fire extinguisher before it’s too late.

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Sean, as the car is a saloon feel free to move the post back to the XJ list by using the pen icon on the heading.

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are you positive about you got the right cap and ignition loom ?
with new parts, wires and cap insulation should be ok, and sparks only occur at the plug (even with wrong timing)

check the cap and all wires to the plugs are seated completely, as is the wiring to the coil (s?)

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Hi Sean,

First, with your permission I will move the thread to the V12 section, I think it’s the most relevant.
It will be a well travelled thread!!

Remove the distributor and make sure it’s sparkly clean inside. Any moisture or oil deposits can divert the spark.
Measure the resistance if the spark leads and make sure that they are properly seated.
And are your spark plugs good?


Sean, based on the description and appearance of the engine, I would replace the original looking ignition wires, and the spark plugs. High resistance in the wires, and questionable eroded large gaps in the plugs will encourage sparking around the cap as the current will look for the least resistance path to go to ground. Cleaning all the connecters on the coils would be a good idea, also.


Sean, Replacement of cap, wires, etc. would be the best course of action IMHO. Before doing that start the motor (hood up) in a dark place (i.e. garage without lights on), noting where sparks are coming from. If it ain’t broke, don’t fix it! Probably bad wires but the “dark” test will reveal a lot!

Happy Trails,


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The v12 list seems the appropriate forum in my mind

Welcome to Jag-Lovers!
We have two V12 Jaguars, a Canadian Market 1990 V12 Vanden Plas (Series III XJ12) similar to your Canadian market 1986 V12 Vanden Plas, and a 1990 XJ-S convertible. The engines are similar but there are also significant differences in them like the ignition systems (XJ-S has Marelli and XJ12 has Lucas). The Jag-Lovers XJ list members primarily own XJ6s, and many are unfamiliar with V12s so I will often go to the XJ-S or V12 lists as appropriate when looking for help on my XJ12. I recommend that your V12 engine specific questions are best addressed on the V12 list and that Series III saloon specific questions not directly related to the engine are best directed to the XJ list. In any event, I recommend that you always include the model year and engine type somewhere in your posts to avoid any confusion about which car you have that you are asking about since most members are likely unfamiliar with your 1986 Canadian market V12 Vanden Plas. You saw how easily that happened in this thread.
Do you have copies of the Jaguar Series III Service Manual, the 1986 V12 Vanden Plas owners manual, the Jaguar Series III XJ6 S57 Electrical Guide, the Jaguar XJ-S Repair Operations Manual and a copy of the Jaguar Series III XJ12 Parts Catalogue? If not, then you should get copies because they will take a lot of guesswork out of working on your car. I found most of my hard copies on eBay and I see them there from time to time.
As a matter of safety I recommend that you immediately replace all of the engine bay fuel injection hoses in your car and do not try to start the engine again until you do. From the engine bay picture that you provided it appears that your fuel injection lines might be original from 1986 and they are absolutely not to be trusted with fuel injection pressure after 37 years especially since you are experiencing electrical sparks at the nearby distributor. The longer fuel injection hoses with the metal fitting on the ends connected to the fuel rail will have date stamped tags on them. Inspect one of the tags and see if it has a 1986 date stamped on it. Some of the USA based Jaguar parts suppliers like Moss Motors, Welsh Enterprises, and SNG Barratt sell fuel injection hose kits for the V12 engines. You do not need an engine bay fire to add to your many challenges.

Good luck.




Wise words (cautions) from Paul. I’d suggest heeding his advice. Without a required replacement schedule parts/components and things like fuel injector hoses are overlooked. Overlooked until one (or more) fail, causing a catastrophic engine bay fire. A couple of $$ and a couple of hours DIY labor means a lot of peace of mind. Same goes for coolant hoses and vacuum lines. If you’re new to the car replacing those will put you far ahead down the road. Most PO’s don’t record what maintenance (hose replacement, etc.) they do so you have a big slate of unknowns. Take Paul’s advice and replace the high pressure fuel injector hoses at the very minimum!

Happy Trails,



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