The best suspect is fuel pressure is dropping when the engine is off. It should stay up for days or weeks. To verify this, turn the ignition switch on, wait for two or three seconds, (you might hear the hum of the fuel pump for one second), turn it off, wait a few seconds, then turn it on again and crank the engine. If that helps, it's because fuel pressure needed to build up enough for the engine to run. The pump runs slower than normal during cranking, so pressure builds up slower.
The best suspect for losing fuel pressure is a leaking injector, but a leaking fuel pressure regulator or a leaking check valve in the fuel pump can do that too. You can connect a fuel pressure gauge to see what happens to fuel pressure when the engine is off, and when you try to start it.
I will be leaving now to hibernate overnight! HMAC300 will give you some guidance if he is watching for your next reply.
Saturday, December 31st, 2016 AT 3:07 PM