Practically Classics Forum

It's also typical of the symptoms shown by faulty caps in the ignition amp, especially when it's the type with two separate lens as supplied for the distributor on these V8s, assuming it hasn't been replaced by a single contact version.

Just because the original Lucas Opus amp has been replaced by the Lumenition (Optronic I assume, since you'd need two Magnetronic units for this application), don't assume that the amp or either of the lens are without fault, especially not if the Optronic system was old stock. Also check the connections between the amp and the loom that comes from the lens assembly, they're very prone to poor contacts and will, as anything where there exists an unintended high resistance, display their fault once warmed through.

It sounds like it's missing a cylinder, pull plug wires (without shocking yourself ) one by one and replace. The one that does not change the tone of the engine is the problem cylinder. First try to replace the plug then wire and then run a compression test.

I've replaced all plug leads and that made no difference. Also, I used the Colourtune kit on 2 different cylinders and they both fired randomly.
I'll check the other cylinders too. If all of them misfire, it can be narrowed down too the coil (replaced already), the ignition (replaced already) or the distributor (cap and rotor replaced).

If the ignition amp is an Optronic, then the fault is almost certainly the decoupling cap C2 and/or its associated resistor in the amplifier board or a poor connection in one of the multiplugs between the lens (or both if it's the type of distributor that had two sets of contacts prior to being converted) and the amp. It's the only thing that would be so random, I'll assume that there are two lens as it hasn't died completely, so check both plugs where the amp connects to those phototransistors' lens.

Hi did you find the problem in the end because I have the same issue