Originally Posted by Ski-me
It's a EFI, Mercury Scorpion 330HP engine. I think that's sequential injection, not TBI if I recall.
I'll check with her on the fuel pump turning on with key before start-up.
Nothing major on engine other than a few minor tune-up parts (plug, cap, rotor, fuel filter). However he did install a new alternator and possibly a new grounding wire......however, it was still behaving this way prior to his repairs.
Someone needs to verify fuel pressure and quality, as well as spark, when it won't start. I have seen ground wires that were loose/broken and when the engine compartment temperature was high, the wires relaxed, breaking contact with the block and when it cooled, it was fine. Could be a connector that's doing the same thing.