Intermittent misfire on Series 2 V12

[mike020150]

For some years I have had a slight but intermittent misfire on my pre HE fuel injected V12. Being intermittent has led me to many false solutions! The original ignition amplifier was mounted on the engine. When it failed in the nineties, I 'upgraded' to the remote version which I mounted above the radiator. Having eliminated other misfire possibilities, my most recent suspicions centred again on the ignition system. Tossing up whether to go the Barratt's route and replace the amplifier together with the distributor or to simply change the amplifier circuit board for an upgraded Reopus version with its revised Hall effect pickup, I chose the latter option. Derek Watson was selling the Reopus kits for £250 at Stoneleigh versus around £500 for the Barratt's more comprehensive conversion. Had I needed a distributor, I would probably have chosen differently. One of Derek Watson's team transferred the wiring from my car's original amplifier circuit board (I'm not very good with a soldering iron and never throw anything away!) making fitting the Reopus modified amplifier and distributor pick-up straightforward after I'd returned the car's wiring to factory standard (long wire amplifiers are five wire versions whereas early originals have six wires, the difference being how the rev counter is triggered). The good news is that, so far, there's no sign of the misfire. The even better news is a very definite increase in smoothness and willingness to rev from the mid range upwards despite changing nothing else. Being a cynic, I have left the old amplifier (which passes all the workshop manual tests) in place and should there ever be a Reopus failure, I will refit the matching distributor pick-up and connect the wiring to ensure I can get home. For anyone with a car plagued with similar ignition related symptoms, the moral of the story is that, today, not only the supposed reliability but also the operation of the 1960's designed Opus ignition system for the V12 can be improved upon. Mike.

[oldtimer]

Hi Mike 020150,
I was just back tracking a bit and came across the above written by you back in April which I found most interesting and relevant to my situation

I have owned a '73 XJ12 L on Stromberg's for about 40 years, during that time the Opus ignition has performed without issue. As we know the Opus system has been dubbed Opeless but I cannot share that view. However the car has been neglected for some time especially during the past eighteen months to the extent that it has not even been started. Fortunately it lives up on the four post lift with the battery permanently on charge.

In the last few days I have been in the process of getting it going. It actually started promptly with a great deal of popping and banging. After shut down I stepped out of the car into a large pool of petrol. After removing the intake trunking and a couple of dash pots to mop up the surplus fuel and ensuring the float chamber was doing what it should I tried starting again.

This time much better but cylinder 3A dead. A new lead and plug connected (old plug still in 3A) and plug laid on cam cover -still dead . Same with 1A, this time big fat spark. Surprising how well it ran on ten cylinders.

I concluded it must be the timing rotor, I discovered one of the ferrite rods on the periphery of the rotor have broken in half and protruding out. A new rotor received from SNG Barrett within twenty four hours fixed the problem.

Coincidently I have just read a very interesting article in connection with the Opus system and despite the fact that the car is running as sweet as ever I am debating whether it is time to take advantage of the later style of switching gear employed in the New Zealand made Re Opus.

I need to do a bit of agonising first but would be interested if you have anything to add

Oldtimer

PS I think the Mercury switches are starting to take effect ( private joke folks)

[oldtimer]

Hi Mike 020150,
I was just back tracking a bit and came across the above written by you back in April which I found most interesting and relevant to my situation

I have owned a '73 XJ12 L on Stromberg's for about 40 years, during that time the Opus ignition has performed without issue. As we know the Opus system has been dubbed Opeless but I cannot share that view. However the car has been neglected for some time especially during the past eighteen months to the extent that it has not even been started. Fortunately it lives up on the four post lift with the battery permanently on charge.

In the last few days I have been in the process of getting it going. It actually started promptly with a great deal of popping and banging. After shut down I stepped out of the car into a large pool of petrol. After removing the intake trunking and a couple of dash pots to mop up the surplus fuel and ensuring the float chamber was doing what it should I tried starting again.

This time much better but cylinder 3A dead. A new lead and plug connected (old plug still in 3A) and plug laid on cam cover -still dead . Same with 1A, this time big fat spark. Surprising how well it ran on ten cylinders.

I concluded it must be the timing rotor, I discovered one of the ferrite rods on the periphery of the rotor have broken in half and protruding out. A new rotor received from SNG Barrett within twenty four hours fixed the problem.

Coincidently I have just read a very interesting article in connection with the Opus system and despite the fact that the car is running as sweet as ever I am debating whether it is time to take advantage of the later style of switching gear employed in the New Zealand made Re Opus.

I need to do a bit of agonising first but would be interested if you have anything to add

Oldtimer

PS I think the Mercury switches are starting to take effect ( private joke folks)

[mike020150]

Hi Oldtimer,

I've now driven nearly 3000 miles with the Reopus modified amplifier in place and so far, at least, it's all good news. I can't say that it has added any noticeable MPG improvement but cold starting is a fraction quicker; hot starting is stronger; and idling is smoother at lower revs. The load of the aircon compressor cutting in no longer causes a major stumble at idle and she revs more freely as I recall she used to do years ago (I had begun to think I my memories were held in a rose tinted file). Finally, like all good insurance, I haven't had to make use of my long lead amplifier mounted over the radiator!

On the subject of timing rotors, beware modern replacements. Early rotors were drilled blind so the ferrite rods couldn't fall out. Current ones are drilled completely through and the ferrite rods held in position with a blob of glue. Guess which is the better solution? Mike.

[mike020150]

An interesting postscript about the Reopus unit. Last year, when I took the car for MoT just before fitting the Reopus, the average CO reading between cylinder banks was 2.2% (original Jaguar setting 2.0% max) and the idle quality showed all the signs of a weak mixture. This year, not having touched anything except for upgrading the ignition amplifier, the car achieved 1.5%/1.6% (left and right banks) with a better idle quality. These are the best readings I have had in 34 years ownership! Mike.