John S Farrington
Jedi Warrior
Offline
The Marelli ignition in the later models of the V12 has an identified problem/failure mechanism of the unique distributor cap. I have just experienced this problem and it is scarey. The distributor cap can develop an open circuit in the right hand (B bank)secondary circuit. This causes the ignition spark to not arrive at the 6 spark plugs on B bank. It does not shut off the fuel injector signal. If the car is in a cruising mode with the catallytic converters heated, this situation may be catastrophic and cause an engine compartment fire. The unburnt gasoline passing through the B bank cylinders arrives at the very hot catalytic convertor on the right hand side of the engine which adds to the heat with active combustion and very soon the cherry hot glowing convertor will ignite anything in its surroundings. In my case I detected the smoke and immediately shut down the engine. An insulated cable had already started to burn. The presence of a fire extinguisher saved the day. This is not a good situation!! It is applicable to catalytic equipped V12s with the Marelli ignition. I recoommend the following to protect your car and yourself:
1. Change out the distributor cap and rotor at least every 50K miles.
2. Do not use anything except an ignition cap that is a Jaguar original part. (my cap was Jaguar original but I understand that aftermarket brands fail a lot more often than OEM).
3. If your local regulations (state) permits it, get rid of the catalytic converters on both sides ASAP. Replace them with European down pipes from the manifold. If you opt to gut them, make sure that all of the material is removed from the converter body.
What exasperates this situation is that my failure mode turned out the be the inner contact ring of the cap burning out. This is yet another mode since I have also heard that the cap can develop an internal separation between the coil lead junction on top and the inner ring on the bottom, good grief!! If you like your V12 in its current unburnt condition, pay heed. Jack
1. Change out the distributor cap and rotor at least every 50K miles.
2. Do not use anything except an ignition cap that is a Jaguar original part. (my cap was Jaguar original but I understand that aftermarket brands fail a lot more often than OEM).
3. If your local regulations (state) permits it, get rid of the catalytic converters on both sides ASAP. Replace them with European down pipes from the manifold. If you opt to gut them, make sure that all of the material is removed from the converter body.
What exasperates this situation is that my failure mode turned out the be the inner contact ring of the cap burning out. This is yet another mode since I have also heard that the cap can develop an internal separation between the coil lead junction on top and the inner ring on the bottom, good grief!! If you like your V12 in its current unburnt condition, pay heed. Jack