Almost certainly a "Marelli" ignition failure. Could be one of the coils or control modules. Or rotor failure.

I begin by pulling the distributor cap to inspect the rotor. It might be burned-thru

Cheers
DD

 

Following up on Doug's post...You can't just pull the distributor cap and "look" at the rotor. You must unscrew it and look underneath as the burn can be hidden from the top. If burned, read up on the "Silicon Squirt" fix in Kirby's book. Essentially, you cut the top of the distributor shaft and fill the bottom of the new rotor with silicon and put it on the shaft, preventing future burn through.

 

I am not a proponent of the "Marelli Modification" If the ignition is maintained properly you will not have problems with the rotor burning.

The burn is in my opinion caused by either faulty/old spark plugs or ignition leads. We are dealing with High Voltage and it WILL find the shortest path to ground. If the leads and plugs are in good condition this is the path of least resistance. If a couple of plugs are old and not firing then the voltage MUST find a path to ground and this could be via the rotor body, especially if it has carbon buildup on it.

When I bought my car I replaced all the plugs and the front 4 (under the AC compressor) looked like they had never been replaced. The electrodes were totally eaten away. The most worrying bit was the car was always serviced by a Jaguar dealer.

Now I have my rant out of the way.

The tacho runs off the A bank coil so you definitely have an ignition issue.

Do as Doug said and pull the dissy cap and remove the rotor. Inspect the rotor and terminals in the cap. Replace either if needed. If these are good then look at the wiring from the ignition modules to the coils this gets crunchy and the insulation breaks down.

I would recommend replacing ALL spark plugs and ignition leads. My car does not do a lot of miles these days but I still pull the plugs every year and check and/or replace them. I also remove the dissy cap and check it and the rotor. My car has 300,000km and I have done 100,000 of that and I have not replaced the rotor or cap.

 

Hi Nick

Just to expand on what has been said, do be very careful when removing the Rotor from the 'Dizzy' where it is very important to hold down the part underneath, if you are intending to pull the Rotor off or you could break the springs inside

Which could drop down into the 'Dizzy' which could cause you a whole World of problems and as has already been said, one of the main Suspects, is the failure of changing the very hard to get at Spark Plugs underneath the A/C

If you have to replace the Rotor and Cap, then it may be a good idea to put a little Silicone into the hole where the Shaft goes into the Cap

But if you want to go the whole 9 yards, then I think that 'Safari' may have the Ultimate Fix (see link)

As for me, I don't have 'Cats' and always renew all the Spark Plugs and wouldn't feel very comfortable about cutting the Rotor Shaft, although I did give the 'Dizzy Cap' a little drop of Silicone where the Shaft on the top of the Rotor

Goes into the hole in the Cap

Here is the Marelli Fire Fix, that 'Safari' came up with 'Safaris' Marelli Fire Fix