Simon's new Xantia V6 and Leaf blog

[DHallworth]

It’s going to get a fairly major service as it comes out of hibernation this summer and the plug leads were on the list of things to be replaced. It’s certainly running well enough with the new coil pack installed anyway

[Stickyfinger]

1 video of each coil pack is merged into 1 here:

Shocking

[Mandrake]

Again... in the darkness of the workshop all became apparent! Neither coils had cracked or broken plastic but both were arcing in the same place!

Interesting that it's happening on the same place on both! I can't say I have seen that on mine, but I haven't tried running it with the cover off in the dark, might be worth checking.

I ordered 2 new replacement coils and replaced them on both cars and they've not given any problems since... not that they've been driven anywhere right enough! Although I am thinking of having the XM MOT'd this week.

Where did you order from and what brand ? The only brand new one I've ordered before was NGK and I'm not happy about the fact that 8 years later it has an intermittent failure of the primary of one of the coils.

The current was finding it easier to jump that air gap than the spark plug. I would suggest that you check or replace the ignition leads. I know that is a pain.

Yes, it's extremely likely that the leads are faulty on David's cars. These leads are carbon resistance leads with a normal value of around 3k ohm.

I had to replace the ignition leads on both my V6's for the same reason - they both had at least one lead that was open circuit, measured with a multi meter.

The spark energy will still try to jump the break within the lead itself, however by doing so the voltage available at the spark plug gap is correspondingly reduced.

The required spark voltage at the plug increases when you open the throttle and increase the cylinder pressure, therefore when the potential spark plug voltage is unusually low (due to breaks in the leads that it is having to waste energy jumping inside the lead) the engine will run fine under low load but you will get a single cylinder misfire and lack of power when you put your foot down.

Without an automotive scope it's actually pretty hard to diagnose this accurately so in these circumstances and given the age of the cars I would just replace the leads and cassette - it's actually not a bad job and it gives a chance to check for oil in the rear spark plug wells.

The lead for the left hand coil must be pretty stuffed to allow a spark of that length to jump outside the normal path, because that is a much larger gap than the combined gaps of the front and rear spark plugs...

[DHallworth]

Last time I replaced the leads I bought them from Citroen with the cassette.

They are now obsolete though and I cannot find any that come with the cassette that secures over the rear bank.

I've done about 150 miles in the XM since it's MOT and am not having any issues with it thankfully.]

David.