Hello,
Can I get some advice on a v12 that seems to run on only the left bank of cylinders? Car was running great then starts sputtering and shaking and losing power. It wouldn't make it up the hill and, hence the flatbed tow. The car will run but it appears to be only running on the left side(hand held behind exhaust pipe, one side fairly smooth and one pulsing). I pulled the cover off the center valley and found no disconnected hoses but did find the throttle position switch wires unused. I can't see where they connect. The switch is mounted on the right side of the throttle capstan and clicks when the throttle is cracked. It has a black and orange wire with an enclosed male plug end. I found an orange wire that is either broken or terminated coming out of a bundle in the valley but no sign of the black wire. So, I have two questions:Could the switch need to be hooked into the orange wire and is it really needed? I'm hoping this has something to do with my original issue but would like to repair things as I discover them.

Any help would be appreciated.

Thanks

 

Hi Treborefir

What you have just experienced has all the classic symptoms of a Marelli Distributor Failure, where one Bank of Cylinders has shut down while the other Bank is still running, hence the inexplicable sudden loss of power

So before we go any further, do not attempt to Start or Drive the Car because it could quite easily burst into Flames

The V12 Engine is just like Two Six Cylinder Engines joined together and inside the distributor Cap you will find a 'Stepped Rotor' where the Bottom one controls one Bank and the Top one Controls the other Bank

Where what appears to have happened, is that the Top of the 'Stepped Rotor' has developed a problem and is shorting to earth, which means that while one Bank is running OK, the other one is now Pumping Raw Petrol into the Exhaust Muffler

No doubt you are a head of me now but if that Raw Petrol Ignites, then your Car could easily catch fire and then burn to the ground (especially if you have 'Cats' which your Car probably has)

So the first thing to do is to remove the Distributor Cap and look in the Cap, where you should almost certainly see where an electrical Arc has tried to burn through

That being the Case, replace the Cap and the Rotor and also a good idea to change all the Plugs, as the very near Marelli Fire which by luck you seem to have avoided, is normally resulting from bad maintainance

Quite often caused by not Changing those hard to get to Spark Plugs, under the Air Con Motor and so it looks as if maybe, you 'dodged a bullet' this time!

 

 

Hi Can you get a Photo of the Wires you are talking about, maybe they go to the Kickdown Switch or something but hard to tell just from description alone

 

 

 

 

Most suppliers stock a half decent replacement, if you somehow find a genuine marelli I'll be stunned. https://www.sngbarratt.com/us/#!/Eng...6-9fc2aa89de18

Your wire thing could be to manually select a retarded fuel map, the orange wire rings a bell but yours is a 6L so there are differences I might not know about.

 

How?

 

 

You were very lucky, that your Car didn't catch fire

No idea about the wires though

 

If you have not already done so, renew the plugs and the HT leads. Poor plugs, says Warrjon who knows, are the main reason for marelli failures.

 

Pull all the spark plugs and check/replace them, also the ignition leads. A rotor failure like this almost certainly caused by a number of cylinders not firing. look at the cap this may give you clue as to which cylinder/s are not firing properly, scorching on the terminals is a giveaway.

TPS only seems to be there for acceleration enrichment and closed throttle running, load is MAP.

 

Hi Treborfir

When you replace the Rotor, hold down the piece underneath it with a Screwdriver, or you 'Could' break the Springs of the balance weights, or disturb them in some way which would then completely spoil your day

You could also put a dab of Silicone in the Top of the inside of the Distro Cap, which could reduce the Chances of the Rotor Arching out in the Future

 

Thanks for all your advice. I took it to heart and have ordered cap, rotor, plugs and a plug wire set. The parts should be arriving by the end of this week, so, I hope to be on the road again by Sunday. I was pretty amazed that the cost for all the above was less than $225.00! All the items ordered were of a quality brand name product. I ordered the plugs with a heat range number 6 but since have pulled some plugs and they have a #7 heat range. They were NGKs so I think they are a bit colder than what I ordered. I ordered the NGKs with a #6 as was advised by the internet. My car runs pretty cool with a newer radiator so I'm hoping it won't be a problem.

Thanks again,

Bob

 

BR7 is what the manual lists.

I know a lot of people in the USA have done what Kirby lists in his guide, but I do not agree with modifying the rotor and mount for the so called "Marelli mod" IMO as long as regular maintenance is performed (changing plugs, inspecting cap and rotor) and there are no wiring issues the car will not drop a bank. Jaguar were not the only manufacturer ti use this Marelli system, Lamborghini, Ferrari and Porsche all used this same Marelli system with small variations. The Lambo guys now use Jaguar cap and rotor.replacements as the Lambo ones are eye wateringly expensive.