Main relay, fuel pump or what?

[solanog]

It has happened to me about four time in the last week. When I try to start the car it won't start. I hear the clicks of the main relay but can't hear the fuel pump while the check engine light is on (couple of seconds after turning the ignition on). I turn the key the car starts for about half a second and dies. Then I keep on trying, even hit the tank and it starts only when it wants to. Once it starts I have had no trouble (and hope it stays like this at least).
This does not happens always, I'm not sure but seems like is more common when little fuel is left on the tank, so how can I determine what's the problem?
The car is a 1999 Civic. BTW a friend told me to tear of the main relay and re solder all the contacts, I did it but I had the failure once after that.

[thermal]

I dont think it's the relay. Does it crank fine? What was the CEL code?

If the motor has no problem cranking over, then it could be a few other things. Have you checked for sparks?

[solanog]

It cranks perfectly, battery is around 3 months old and here in Costa Rica we are at around 20 degrees Celsius that's around 68 Farenheit. Sparks are just about 5000 km old (3h miles).
There is no CEL, the light turns on when I turn ignition on then it goes off normally. When the car does not start I can't hear the fuel pump "priming" when I turn the ignition several times then I can hear the pump and then the car starts with no problem. BTW it has only around 111000km (69000 miles).

[thermal]

So battery is good and no CEL.

It could possibly be your fuel pump. The thing is, you may hear it prime, but the real question is, is it putting out enough volume and pressure to keep up with combustion? I had this problem just recently with my Chevy truck.

Also, replace the rotor button inside your distributor. When the contacts get dirty, if messes up your firing intensity.