Unfortunately I have no cosworth powered friends so every part i want to try I have to buy. I'm also not that experienced with mechanics, especially not diagnostics so am relying on reading old threads about misfiring issues to try and fault find (amazing how helpful the passionford lot are!).

I tried the old plugs on original gap, then gapped them to 0.61 then swapped for denso iridium. I'm not sure if it's rev or boost related, will try and figure it out at the weekend. I do have a boost gauge so should be able to tell.

When the misfire started it would only start to misfire when I put my foot down but would then misfire even on idle.

Now that I have replaced coil, leads, plugs, cleaned crank sensor, dried out middle back connector and timed correctly it runs a lot better and will actually rev for a short while before starting to misfire. It starts misfiring under boost but will then continue running rough at idle and nearly dies when I lift my foot off the throttle.

I have recently upgraded the fuel pump from standard to a bosch 044, wondering whether this might have caused the fuel pressure regulator to fail???

I still think it has something to do with water getting into the middle connector at the back of the engine so am going to try cutting the wires and soldering them together. The fact that there was actually a drop of water inside the connector seems to suggest that it must have seeped through the wiring which can't be good, was hoping a ton of contact cleaner and leaving it disconnected for a week in the warm weather would have dried it but it might not have done if the water has got right into the wiring.

Failing that I'm going to get a sensor kit from msd and swap all my sensors and if that fails i'm going to give up and give it to a proper mechanic because it's my only car and I'm getting fed up with the lack of transport (it's seriously cutting in to my fishing time!)