I have this startup problem on rare occasions in the winter, say once a year. But it started happening more frequently these days (once per week):-
Engine would crank (battery full) but car doesn't start. Would not start after many attempts. But after an hour or so, it starts fine. Yesterday when it didn't start, I rented a vehicle and had mine towed to the mechanic. But when he had his hands on it after few hours, it just started fine (as I might have guessed). He tried it at later times again but could not reproduce the problem. Thus, he says, he cannot diagnose.
How do I go about fixing this one? Start replacing parts, maybe? In any particular order? I had replaced the fuel pump about 3 yrs back. The mechanic did mention about some relay maybe not reliably working, but just a guess.

 

Main relay or fuel pump problems?

Get in the habit of listening for the fuel pump. Whenever you start the car, do it like this...
1) Turn off all noisemakers like blowers & stereo.
2) Turn key to ON, but don't immediately turn it to START.
3) Listen for the fuel pump - it runs for 2 seconds then stops.
4) Turn the key to START ideally just before the pump stops.

If you ever hear that the fuel pump doesn't run, IS THAT WHEN THE ENGINE DOESN'T START??