When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi everyone, hope you are holding up and healthy,
Just out in the 1992 XJS V12 out for a short scoot. I have been on a few short rides over the last few weeks with no issue. Today the idle became erratic accompanied by smoke and burning smell. Farts and pops out of the exhaust and massive power loss. Got home, lots of smoke coming from (very windy hard to tell) exhaust under the car. Ideas on where to start troubleshooting ?
As the V12 is like 2 X 6 cylinder engines joined together, where inside the Distributor Cap is what is called a 'Stepped Rotor' where the Top part operates one Bank of Cylinders and the Bottom part operates the other Bank of Cylinders
What can happened and may have happened in your case is that the Rotor Arm can develop a short inside the Distributor Cap and then Burns out, resulting in a loss of Power while leaving the Engine Running on just one Bank of Cylinders
One of the problems being that Raw Fuel is still being pumped into the Hot Exhaust Pipe/Muffler of the Bank of Cylinders that is no longer Running, which can catch fire and burn your Car to the Ground!
So don't attempt to drive her, until you've got her fixed
Where the first thing to do is to remove the Distributor Cap and look inside the Distributor where you would then be able to see signs of Arching and Burning, which would then involve replacing the Stepped Rotor with a New one
As for the Smell of Burning, that is almost Certainly down to the 'Cat' of the Bank of Cylinders that has shut down beginning to glow red hot! hence the danger of your Car catching Fire
Marelli Fires are not that common and are usually caused by lack of maintenance, like for instance not changing the Spark Plugs under the Air Con Motor which can be a PIA to change and sometimes get left
Hope This Helps and please let us all know what you find when you remove the distributor cap
As the V12 is like 2 X 6 cylinder engines joined together, where inside the Distributor Cap is what is called a 'Stepped Rotor' where the Top part operates one Bank of Cylinders and the Bottom part operates the other Bank of Cylinders
What can happened and may have happened in your case is that the Rotor Arm can develop a short inside the Distributor Cap and then Burns out, resulting in a loss of Power while leaving the Engine Running on just one Bank of Cylinders
One of the problems being that Raw Fuel is still being pumped into the Hot Exhaust Pipe/Muffler of the Bank of Cylinders that is no longer Running, which can catch fire and burn your Car to the Ground!
So don't attempt to drive her, until you've got her fixed
Where the first thing to do is to remove the Distributor Cap and look inside the Distributor where you would then be able to see signs of Arching and Burning, which would then involve replacing the Stepped Rotor with a New one
As for the Smell of Burning, that is almost Certainly down to the 'Cat' of the Bank of Cylinders that has shut down beginning to glow red hot! hence the danger of your Car catching Fire
Marelli Fires are not that common and are usually caused by lack of maintenance, like for instance not changing the Spark Plugs under the Air Con Motor which can be a PIA to change and sometimes get left
Hope This Helps and please let us all know what you find when you remove the distributor cap
Thanks for the advice. Sounds right to me. Don’t know much about this stuff. Based on the pictures does it confirm your theory? If yes do I just change the rotor and cap?
thx again !
If you got home with a Marelli failure, you're very, very lucky. Or you were very, very close. Not having experienced that, I can't say for certain, but I have experienced a coil failure which leads to much the same thing (no spark on one bank), and while the car felt like it was powered by rubber bands, there was no vibration or erratic idle--as the failure of one bank just turns the V12 into a sweet straight-six. Your dizzy look fairly clean, from what the photos show, but OB's right: do NOT attempt to drive her until you know it wasn't a Marelli issue. If it was, you got really lucky.
Pay close attention to the wiring here to my marelli ignition harness had a failed coil plug causing the same thing, thankfully I had gutted CATs so no fireball. I wouldn't even run the engine as is until you've replaced or inspected and confirmed a list of things.
As has been already said, have you got any Pics of the Inside of the Distro Cap and if there are no signs of burning, check to see if its got any hairline Cracks but in the event that you replace the Rotor and the Cap
All of that work could be wasted if you don't change ALL the Sparkplugs or else the very same problem could easily turn up again but next time with more disastrous results, where as things stand you may also find that the 'Cat' on the 'non firing bank' could also be blocked
At first glance of your photos, the Rotor doesn't look burned so maybe ok, though maybe not so with the Distributor Cap
Though in any event don't go throwing the 'Old Rotor' away as even a Second Hand one could be worth some Serious Money, especially if its an OEM Marelli, as not all Rotors are created equal
The cap doesn't look that great. You can see deposits on the outside which are electrical paths to other terminal posts. Also, of the ones I can see, there are at least 3 posts that have very corroded internal receptacles which probably have not been providing good or any high voltage outputs to the plugs. Either clean up the cap or get a new one. If you can get inside of the post receptacles, with a fine wire brush or scotchbrite to clean and shine up the internal receptacles then give the whole thing a good cleaning with dish detergent, it'll look brand new...as long as there are are no cracks which are high voltage leaks which cause cross firing. Don't use scotchbrite on the cap surface itself as that will definitely cause fine scratches on the plastic/Bakelite/phenolic surface and then you will have cross firing.
Of course check the inside terminals too. If signs of burn or arcing, then of course replace.
I do believe you found the problem. Others will be along soon to confirm. I've seen several rotors burn/arc, carbon trac etc. but I believe that's the first one I've seen burn down the center through itself?
Yup! that was a Marelli Fire alright as confirmed by that burned out Rotor
(1) Change ALL the Spark Plugs
(2) Get yourself a New Rotor preferably an OEM Marelli if you can find one which should be Maroon in Colour, as the one you are holding could be an Aftermarket one although it says made in Italy
(3) Clean up your Distributor Cap and check for cracks or any signs of Burning and then replace it if needs be and maybe New Plug Leads as well
(4) Before you replace the Rotor put a dab of Silicone in the Star Shaped Hole before you put it back on its Shaft, as this also helps to prevent Arching
(5) When you've got her all back together and then Started your Car up, if She's Running really rough as opposed to Running like a 'Bird' then the chances are that the 'Cat' on the Bank that shut down may have got blocked or have melted
Are 'Cats' a requirement where you are, as if not you could consider removing them, as an XJS without 'Cats' is far less likely to catch on fire without them
(6) Give Thanks to the 'Jaguar Gods' that you got lucky and your Car didn't turn into a fireball
Jordan - have you checked Palm's book? That's got a lot about avoiding Marelli fires. Also, I don't see "Marelli" written on your rotor anywhere.
OB: Maroon rotor? You sure? I can't find any images of a maroon Marelli.
His cap looks like a shitty aftermarket, which is all we've got now...original marelli caps are impossible to find, and if one comes up its used on Ebay for several hundred USD.
The one that's on my Car is and the GF somehow managed to find a genuine Crank Position Sensor which was also in 'maroon' Stamped Marelli Magneti Made in Italy
but as VancouverXJ6 has also pointed out, these are super rare and hard to find
The closest that you might be able to get are those from 'Intermotor' although I haven't tried one myself
I'm going by the pics in this Jag Lovers Page, which show a beige rotor.
The one that was taken off my car and replaced is clearly aftermarket, as it's essentially identical to OP's, though in better condition.
Not necessarily but the person who would know for sure is ptjs Paul, as this sort of thing is right up his Street but if you look on Marelli's own Website you will see some maroon coloured rotors, though sadly none for an XJS V12 well not at the moment anyway
04-09-2020, 01:46 PM
Power loss burning smell
