2003 F150 4.6 V8 won't start when temp outside is 85 or more, even when engine is cold. BUT accidentally discovered that if someone pushes in on the gas cap, it will start right up. Ideas?

 

Checks are in order to see what is failing.
Is it no power to the PCM?
Is the fuel pump able to run?
If your sure the movement of the Gas cap appears to have an effect, maybe it is a fuel pump ground or connector issue
Do some checks to narrow it down.
Good luck.

 

Double post removed.