Hi.
Noticed misfiring so got a set of plugs and plug leads,
Started it after each plug was changed to make sure I hadn't done something wrong, and after 8th plug change it only runs on 6 probably one bank. Checked front coil and there is no voltage to it when it is running on the other coil. Put voltage across the 2 outer connectors on the coil that mate with plug and there is continuity, not open circuit so coil should be good.
Can you help?
Plug leads available at Rockauto for $30
Norman

 

Hi nofking

You could be on the verge of having a 'Marelli Fire' and so I wouldn't drive the Car until you've fixed it and so remove the Distributor Cap and see if there is any Signs of Burning in the Cap and or on the Rotor

As if one Bank of Cylinders has Shut Down, then Raw Fuel could still be pumped into the Exhaust Pipe/Muffler of the Bank that has shut down where if Ignited could burn your Car to the Ground

While 'Marelli Fires' are not that common, they tend to occur with Vehicles fitted with 'Cats' which is usually down to poor maintenance, such as not Changing the Spark Plugs, under the Air Con Motor where they are a bit difficult to get to

Resulting in the Rotor Arm Arching and Burning the Contact under the Distro Cap

As the V12 is like 2 X 6 Cylinder Engines joined together, where the Rotor Arm is 'Stepped' so that the Top half of the Rotor Arm runs one Bank and the Bottom half of the Rotor Arm runs the other

So the First Job is remove the Cap, check for signs of Burning and then report back

 

Many thanks for your reply.
I take note of starting it on 6 with all the raw fuel.
There is no spark from the front coil although the coil seems OK so the cap might be bad as well but is not the primary fault.

 

Hi nofking

The Lower Coil the RED one is for 'A' Bank

The Upper Coil the YELLOW one is for 'B' Bank

If you tried to swap the wires over from one Coil to the other, She won't Start

 

I know that and didn't do that.
As I have said there are no electrical pulses to the front coil when it is running so the coil does not make any spark.
Norman

 

Check that the non-performing coil has a continuous 12 volt supply to its positive terminal. If it has, then the amplifier is not switching it, or the col is faulty.

 

Good Morning
Thanks for your reply.
I took the plug out of the front, non working, coil and it has only 2 pins. There is voltage to both pins.
Might be a good idea to get a new coil and see if it works?
Norman

 

Hi.
Finally put on a new distributor cap and a new coil but same result still starts on 6 cylinders. Disconnected new front coil and it made no difference.
While it was running I put a meter across the 2 connectors on the front coil plug. No voltage. Put meter on one pin and ground and get 13.4 volts. repeated it on the other pin, same result 13.4 volts. Shouldn't one pin be be grounded?

 

Have you renewed the amplifier on the non-working side? Or connected the working side's amplifier to the non-working side? As Orangeblossom suggested up in the thread?

 

you replaced distributor cap, did you replace the rotor with new one.
i came real close to merelli fire,right bank dead, smoke bellowing from right side firewall, replaced distributor cap and rotor, all was good.
i was lucky it happened at home, if on highway would have burned my jag up.

 

I haven't attempted to switch the coil wires over

 

As I said the forward coil is not producing a spark. It has 13.4 volts on eaqch of its 2 wires when measured from one wire to ground. Suspect the pick-up or amplifier but don't know where to look for these.

 

I put a new coil on the car and still no output high voltage from the coil lead. Each wire to the coil has 13.4 volts when measured to ground when engine is running but thg
at coil has no output. Where and what is the trigger to make pulses to the coil. I need to know what to look for.

 

There is no spark coming out of the new front coil so cannot be rotor

 

Hi Greg.
I think you are correct about the amplifier but where is it and what does it look like. Also what about the sensor maybe on the front pulley which initiates the spark.

 

I am no Marelli person, but I think they are the two smallish rectangles screwed onto the radiator top panel. Orangeblossom and others have posted pics, try doing a search for Marelli amplifier.
Ditto the front crank position sensor, a search will show Orangeblossom's saga. There is also a rear one, if either fail the car will not start.

 

Amps are as Greg says but l don't see the crank sensor taking out only one bank.
If you leave everything else as is but switch the amps over (ie.switch one plug for the other on both) you will probably find the missing spark will move to the rear coil.

 

Hi Norman

On your V12 it won't be the CPS, as neither Bank would run if that were the Case although it could be that one of your Ignition Amplifiers has burned out

There are Two of these mounted on the Front Closing Panel (See Photo) so you could try swapping the Plugs on these around, to see if it gets the other Bank of Cylinders to run

Don't discount the Rotor arm as being the cause of the problem, as this is a 'Stepped Rotor Arm' where one Blade does 'A' Bank and the other Blade does 'B' Bank, so have a look for any signs of 'Burning' which if the case could indicate a Marelli Fire is brewing



The Ignition Amplifiers are the Two Orange Blocks with the Plugs in, try swapping those Plugs over and see if the other Bank runs

 

As I keep saying there is no spark at the wire from the front coil to distributor. I put a spark plug in the coil wire and turned out lights while it was running on the other coil.
No spark.

 

Hi Orangeblossom.
Found the amplifiers and switched the plugs. Still ran on the rear coil only. Put a spark plug in the HT lead out of new front coil and still no spark.
Both amplifiers were slightly warm where they bolt to the heat sinks after a couple of minutes. Took both amplifier plugs out to make sure I was on correct bits and it wouldn't fire, which is what you would expect..
Put an ohm meter across the 2 connections on the new coil and it showed continuity.
When it is running the plug to the front coil which has just 2 connectors, both show 13.4 volts to ground.
Could I have a short between these wires somewhere from the amplifiers?
Many thanks for your help.
Norman