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