Here's a puzzle. My 91 Civic starts every time, all winter long, or if in the shade in the summer, or garage etc. BUT if it sits out in the sun for awhile and is hot, it won't start. When you turn the key on, the fuel pump should run for 5 sec. then turn off, but when it's hot, that inital 5 sec doesn't happen. If you keep trying it, eventually, it will work and start. We've replaced the fuel pump relay and the fuel pump, but it's still a problem.

Any other ideas?

 

welcome to the forum. Check the main relay, or the distributor

 

Is there any problem while driving in hot conditions? I mean, say, you start your car under normal temperature and then take the vehicle out in hot sunny weather, do you sense any change then?

 

No, there's no problem driving it on a hot day, once it starts, it runs fine.

 

After many hits and misses, it turns out this problem was simply the gas cap. The one that was on it was not factory and it didn't allow the tank to vent. When the car got warm and wouldn't start, if you'd open the gas tank, it'd start right up. A new venting gas cap and the problem seems to be solved.

 

Glad you found out what it was ,to bad it cost you a fuel pump and relay.Some time it's the simple things that cause the most problems.