Misfiring when warm

[Tacchino]

Have a 4.5 Cerb that's recently had a tappet service.

When you start from dead cold she runs fine on all cylinders.
Go out for a spin and after a couple of miles the engine misfires on load (even very small load!).

Tickover is great when warm, without any sign of misfiring.
Let her cool down again and the misfire disappears until things warm up after a short run.

I know it's not a good idea but I've tried giving the car a little bit of juice when not fully warmed up and there is no sign of misfiring!

Any ideas on what this is likely to be or in what order I should start replacing parts!
The battery is fully charged when this happens.

Cheers guys.

[Tacchino]

Just had a thought!

If it's a coil pack issue, are the 4.2 and 4.5 items the same Citroen part?

[Choo]

Before changing the coil pack try a new set of HT leads, had a similar problem and this was the fix.

[Keithyboy]

. . . many moons ago I had the same issue - coil packs. They cook nicely in the V of the engine!

[scotty_d]

Plug the lap top in first and take it for a run and data log a good run through the whole rev range under load. (well see if any thing flashes up right away. If nothing shows up plugs and leads first. then coil pack.

[Nigelbs1]

Defo change the leads first their only good for about 6000 miles and should be changed every service. I have had it happen twice now misfire/not firing on all 8 on light load was the leads every time. Oh and while you've got the leads off change the plugs as well.

[Tanguero]

Plugs should have been changed and HT leads checked at the 12k service when the valve clearances were done.

If it is only a problem when warm and only since the clearances were adjusted I would talk to whoever did the service ASAP. Things expand when hot and I would have to wonder if the misfire is possibly related to a clearance closing up too much or something. I would get it checked in case of it causing damage.

[Nickccc]

Make sure the plug leads are seated all the way on. Sounds like something expanding when getting warm.
I had to cut a bit of the rubber insulation off as it was not making a good contact onto the spark plug.

[Nigelbs1]

Many a TVR mechanic has also told me the moment you take the leads off espcially if they have been on there for a while, thats the end of em and stick a fresh set on. They corrode very quickly and whilst on the car may function properly but the moment you pull em off thats them fecked.