By way of an update
Rob from Black Dog attended as promised and proved to 99% satisfaction it was indeed the high pressure fuel pump at fault (didn't always blow the fuse but it certainly wasn't working, no fuel pressure on fuel rail, quiet when ignition on etc) Rob took the old pump and ordered new one which arrived early next day, back at Black Dog he was able to apply power to the pump (once removed from the housing) and it only responded with a click, didn't run at all hence 100% it was at fault. New pump fitted, first turn of key and away she goes
(why I'm going to fess up to this with Smashie & Nicey listening in I'll never know but it might help someone)
Launch on Saturday (having run engine again on muffs beforehand) trickle out of harbour, boat up onto plane for 200 yards, then misfire, revs drop, then engine stops. Try to restart, turns over nicely but no firing, do usual things and find fuel bulb soft and empty (meanwhile and of relevance later get son to check killcord, neutral etc) no amount of squeezing bulb will prime it, check fuel in tank and yes plenty there (was begining to think it'd been nicked!) At about this time son reports Opti gauges have once again gone out and engine won't now turn over i.e. all power lost. 12v systems all working though and 12.4v showing on fish finder, I guessed that trying to restart with no fuel has blown the pump fuse, weak I know but couldn’t think what else could have happened. Anyway get back in (I’ll leave out the embarrassing bit about paddling and being towed) recover boat (won’t mention filling boots with water either because I had to get behind the Rib on the slip to tilt the engine manually)
Once ashore look in detail and can see that my water separating filter is empty of both water and petrol, when I first broke down last week I’d emptied the filter to check for debris/water (there was none ) and then reaching down into the console had closed the bleed valve, except of course I hadn’t closed it, I’d opened it fully! In my defence you can’t really see it very well in the console but as I screwed it in it stopped dripping petrol (course it did it was empty) no wonder the fuel bulb wouldn’t prime it was happily sucking air in! So valve closed by screwing it out fill filter with petrol pump bulb and system primed, change engine fuse and we’re ready to try again
Get boat back on slip trim engine down, go to start and –nothing, all power gone again, boat back up slip cowl off and same fuse blown, that’s without trying to start the engine this time, last spare fuse (thanks Rob)goes in, son touches trim button on throttle and pop, fuse gone. That’ll do for me as well so off home we go, ring Rob who advises that the routing in the wiring in the merc throttle control can cause problems with chaffing and seems like a good place to start so, disconnect trim tilt at engine end, replace fuse and she starts on the button no problem, last thing last night I start on the control box and find chaffing on the shroud that goes up into the throttle handle and lo and behold copper wire exposed on the blue/white cable inside, yep the trim/tilt one.
So yes I had a dud fuel pump which caused my initial breakdown but thrown into that was a second intermitent fault, the chaffed wire which played hell with my fault finding logic!
We, uh, won’t mention the fuel filter ‘issue'