[CharlesJones]

Thanks for all the responses guys. This is all a very interesting discussion. So just to recap to make sure I am understanding this right - the DME just takes a cue from the reference sensor at start-up to locate TDC, and then (possibly - under discussion) checks this occasionally after start-up, whereas the speed sensor is used continuous to track the speed of the engine so the DME knows when to ground the coil for spark and when to trigger the injectors?

Ingo - thanks for the diagnostics tips. Indeed with my no start issue the engine was completely dead - it would crank of course but there was no attempt at firing at all, and not even a hint of unburnt fuel smell, so I guess the injectors weren't doing anything either. What I will do next time it fails is fiddle with the sensor cables and plugs, try it again, and if that doesn't work then fiddle with the DME relay, and then try it again. When it started yesterday I had actually physically touched both of these things prior to the start, so I can't isolate either one.

I really hope its not the DME itself. If fiddling with both the cables and the DME relay doesn't have any effect the next time the problem resurfaces (of course, they might have nothing to do with the problem - if might just have been coincidence) then perhaps I will just send off the DME to a company to have it checked over. Its not something I would have the confidence to attack with a magnifying glass and soldering iron!

Thanks again for all your responses. I will update the thread if I have any more news.