Another Marelli Ignition Caused Engine Fire?
 

Started my car and warmed the engine for 5 minutes from cold. Smelled burning odor as I pulled from curbside. Saw smoke and noticed lack of power. I immediately pulled into a parking lot and shut down engine. Passenger side catalytic converter was glowing red and caught something on fire, as ash and debris dropped under car. I called 911 and Fire Department responded to my location in minutes. Damage seems light, as flames burned out on their own,before the FD arrived. I had my car towed to my repair shop. Sounds like classic Marelli Ignition Failure to me. Hopefully it’s just the cap, rotor, coils to replace. Maybe The catalytic converters too? I don’t know yet what burned. The ash pile was small. Any thoughts? My last XJS also burned from a injection hose. I love this model, but may switch to a XKR if insurance totals car. I think it’s a simple fix. 91 XJS V12 Convertible, Classic Collection.

Almost certainly a Marelli fire. The CC will be toast too as they melt and block up. New HT leads and plugs as well as the things you mention, and it might be that the amplifier on that side it failing. I have no personal experience, but I seem to recall that the Aussies on here who have, say the failures are mainly due to not regularly replacing the plugs and HT leads.
Greg

Greg...Can the catalytic converters be eliminated, rather than replacement?

No as it will just drone. You'll want UK down pipes with a lambda sond bunt welded in.

THe Marelli 'fires' occur due to lack of maintance. How long ago did you check the ignition? When was the cap and rotor checked or even replaced? The parts aren't expensive. This is now going to be quite very expensive.

Just got the car in late November, and only put 500 miles on it. It's been a well maintained car, purchased from the original elderly owner with 78,000 miles. I just changed the fluids, transmission filter, kickdown microswitch, and vacuum modulator. It's been running superb....then poof! Insurance should cover the repairs.

I think you can, but it is best to remove them and weld in a normal pipe, rather than just gut them; so as Daim said, it might be easier and cheaper to get UK spec downpipes with a bung hole for the sensor welded into them. Try David Manners, or there are stainless versions easily available.

May I make a reference to an article by Roger Bywater ( AJ6) on Marelli Failures ? He would claim the word "another" is misplaced.
Having experienced a Marelli rotor arm failure , I find the expression a "lack of power" somewhat understated.
The expression "well maintained" has little relevance when the maintenance schedule does not advise the replacement of a part like this systematically.
For the inconvenience a failure causes I would suggest a replacement of the rotor arm every few years. Any one wish to be more presice ?

I was lucky, in my driveway,started car and noticed smoke coming from passenger side firewall and lack of power, turned it off. Distributor cap, rotor buttons bad, also replaced top coil, the bottom coil I can't get to it so I will jury rig the new bottom coil.
If I had been going down hiway fire would have surly happened.
I still need to replace all fuel lines to the injectors.

Yep. Totally agree. HT leads, plugs, rotor and cap inspection every 2 to 3 years or ~15k miles latest.

I doubt many drive their V12 more than 5k miles a year. If you do, my respect! ;) My cars all had their plugs changed every 60k km or 3 years. As the V12 is less likely to run as well as a modern engine, a more frequent inspection is required.

Yeah, only some XJS enthusiasts and seasoned Jag specialists know to keep an eye on the Marelli ignition.

It's an unusual situation. On most any other car a neglected ignition system may cause a variety of problems....but engine fire isn't one of them. Those accustomed to waiting for the car to 'tell them' when something needs attention are not expecting the message to come in the form of smoke and flames :)

Keep a spare cap and rotor on the shelf. Inspect existing cap and rotor as previously suggested; replace when inspection reveals a need.

Spark plugs and spark plug wires play a big role as well. I'd say 24k miles on plugs and 48k on the wires....but that's a bit arbitrary. I dunno. But when in doubt, replace them!

Cheers
DD

My car is still on its original cap and rotor 160Kmiles on the clock, The Marelli issue seems to be a USA phenomenon as I have not hear of any Marelli cars burning here in Aus.

Based on the 6.0L spare engine I have (came from a USA car) with less miles than my 5.3L and not one valve sealed properly, the whole valve train had to be replaced. I wounder if the USA cars with the cats in the downpipes caused a lot of these issues.

It would be interesting (and rather reassuring!) if the Marelli fires are a US-only thing--pointing to something in the US spec, whatever that might be.
My cap and rotor were replaced at the beginning of the year, but it's not that easy to find caps at least these days (my rotor looks fine, so I kept it). And from what I've read, aftermarket parts are more likely than not to make things worse. I, too, wonder just when your cap and rotor were inspected last. There are, of course, various proposed preventative methods listed in Kirby Palm's book.

For what it's worth, posts about people experiencing Marelli fires seem pretty thin on the ground here. Still, one of the first things I bought was a fire extinguisher, kept behind (or under) the passenger seat so I can get to it reasonably easily. Personally, I'd probably be more worried about old fuel injector hoses in a pre-facelift. Either way, the V12 will get you....

While I haven't had a Marelli fire, I have had one coil go out, and the loss of power when one bank stops working is very, very noticeable indeed. The car isn't sluggish so much as you wonder if the accelerator pedal actually is still connected. In my case, it was just after I started driving, so I managed to get the car back, by which time the Exhaust Temp light was on and the car simply stopped of its own accord. Some smoke from the bung coil, but no fire, luckily.

Interestingly, Japan-market cars have an Exhaust Overheat warning light, which other market cars don't. There's an explanation on the sunvisor about what to do if it comes on (Stop the car! Now!). Hopefully, that'll provide some warning....

I can't think of anything offhand....but I'm only two sips into my first cuppa coffee.

It might come down to the specification of the owner rather the the specification of the car. Lots of Americans have a nonchalant view of preventative servicing.* Plus, these old Jags are dirt cheap in the USA. People buy 'em because they're attracted to shiny objects...but don't have the resources and/or interest to fuss over them.

Also, I'm betting that more XJSs were sold in the USA than any other market. This might skew our perceptions.

Also again...is there such a thing as a Marelli XJS *without* catalytic converters for non-USA markets? If so, then there's nothing to meltdown, glow cherry red, and cook the car !


* I knew a guy, years ago, who bought a gorgeous XJ40 V12 for the wife. I warned him about the Marelli issues but his idea of 'proper servicing' went only as far as lots of oil changes and twice-a-month waxing of the paint.

So in love with this Jag was he that a couple months later he bought a nice XJS...with Marelli ignition....for himself. More warnings from me.

Sure enough, the XJ40 suffered a Marelli failure. Cost him a ton of money at the dealer for new converters....plus cap, rotor, tune up.

More warnings from me. Ignored.

Three months later the exact same scenario happened with his XJS!

But.....those two Jags had the cleanest oil and shiniest paint you've ever seen :)

Cheers
DD

Mine is a UK model Marelli from 89. No cats from factory. No lambda sonds. No emissions gubbins :D

Marelli fires are not common here BUT they happen. Again, due to neglection.

Here is an excellent Post by 'Safari' on how to prevent a Marelli Fire

https://www.jaguarforums.com/forum/x...photos-135024/

Mine is a 1990 with Marelli ignition and no cats.

This is the article in question:
V12 IGNITION SYSTEMS / AJ6 Engineering

It might be an idea to list ways to detect if the V12 isn't running on all twelve cylinders.
Offhand, I think holding a card to the exhaust pipes works, or listening to the injectors clicking by holding a long screwdriver against them and your ear, but these aren't terribly useful while actually cruising down the road at high speed. Or any speed, really....

A card to the exhaust isn't foolproof because if one bank isn't firing, it will still be pumping air/fuel mixture through it, albeit at a much reduced volume to the functioning side.

Listsning to injectors won't tell you if the plugs are firing either - that's the problem, the injectors pumping fuel into a non-firing cylinder just pushes combustible mixture into the cat.

If you have a misfire on one or two cylinders you are unlikely to be able to detect it unless you are very sensitive to vibration and noise. If you have a whole bank out, you are unlikely not to notice unless you are completely unaware of what's happening around you.

So much for my guesses. So how would one detect a misfire in a V12? Even if the car's stationary and you can access the engine.

It's not hard on a cold start... If there is a quick pause in steam pulses, you know one side has an issue.

When the air's cold enough for the steam to be visible, I guess.

That means any time under 15°C :D

Wow, if you can detect a pause in the pulses you have my respect. If the car is ilding at 1000rpm (and it's probably more like 1200 when cold) each bank of 6 is exhausting spent gas 50 times per second, so you're detecting a 1/50th of a second pause from a single missing cylinder!

You can see it... Not kidding. You will see a pulse change if compared to the opposite side.

And when warm, ticking over at 650 you can clearly hear it. Try removing an injector lead and you will clearly hear the difference..

Thanks for confirming it Greg!

Running as in getting a spark? If we disregard time/material/aesthetics for a moment would it not be fairly simple to wire in something small on the cap plugs or spark plugs like a series of small wires leading to a small LED panel showing red for no power and green for correct power?

Or even at the coils? Atleast you'd know if a bank failed?

Also as for the Cats http://simplyperformance.com hand-makes proper downpipe replacements, pricey but nice.

I remember a gadget on sale way back in the 70's ; composed of LEDs fired by a wire/coil round the HT leads. But even with only four cyclinders this lacked elegance .
But what could this tell you ?
A bank has failed ? believe me , you know that already !
Another consideration to take into account is how long have you got with this fault before the catalytic converter is converting no longer ? I have read that it is only seconds.
Has anyone an authorative answer to this ?
If you only have seconds you would need electronics sensing the actual spark to stop the injection. Or even better , a fail safe system : not stopping the injection. But it would be yet another thing to go wrong.

Sometimes it’s easier to test for the presence of a by-product.

Thermocouples on the cats with a warning light on at 500F.

Or even easier... just buy a Japan-market one that already comes with an exhaust temperature warning light. (^_^)
(I actually don't know for certain that this does in fact do the same thing, but seeing as it went on when one of my coils went out, I assume it does.)

I don’t think “easier” means what you think it means. ;) Well, perhaps for you!

I would say easiest is having already bought a cat-less XJS. Can’t set what you don’t have on fire. Reaming out the cats works. I don’t detect a drone from the change, myself. New cat-less downpipes is better, but more $.

Best, of course, is regular maintainance.

To be serious for a moment, it's actually quite easy to buy a Japan-market XJS even if you don't live here. Apparently a lot of Brits buy them, as they're generally a lot more rust-free, and there's plenty with the steering wheel on the wrong side for those rebellious colonists.

Removing the cats, however, is not an option in places where they have strict emissions testing. ::Sad Face::

Your last sentence, though, is quite right.

It's quite easy, I had one ignition wire go bad and if you put your hand near the exhaust you can feel it.

If the whole bank goes down then the air exiting the exhaust will not be hot.

I've had an inspiration!

Wouldn't a car with the airpump pipes removed be an ideal candidate for a series of (12) sensors which would allow access to the combustion chamber without cutting and drillings? A series of small sensor probes leading back to a LCD panel gauge in the car somewhere.

Would pressure sensors be the right 'instrument' to detect a troubled sparkplug or misfiring injector? or EGT (exhaust gas temp) type sensors?

The air pump ports lead into the exhaust ports in the head, and not into the actual combustion chamber. But that would be a good way to sample temps! Motorcycle EGTs are just about the right size too.

A 12 channel meter isn’t available. Three, four channel units is silly. Twelve gauges more so! I’d go for a single gauge and a 12 position rotary dial switch. You could spin it to check all cylinders! :icon_rolleyes:

Some electronic solution with adjustable ranges and alarms / switched outputs probably exists..

No air pump on any of my cars but l am certain the drillings only access the exhaust ports above the valve, not chamber.

They certainly do, I plugged them in my 6.0L heads