My friend's 93 Integra won't start a lot of the time during the summer or whenever its overly hot outside.
What could be the cause of this and/or how do you fix it?

 

Check the main fuel relay.

 

Ya the main fuel relay is probably the cause. My girlfriend just had that fixed like 2 weeks ago.

Our mechanic showed us a trick if it won't start: You know that little flat space on the side of your dash when the door opens? If it won't start bang on that a couple times with the side of your fist and it should start right up. Not a permanent solution, but in case you are stuck somewhere. He did that to my girlfriends car because it wouldn't start and he needed to move it; worked like a charm.

 

Does the motor turn and turn, but no go? Then after some time, especially when doors are open, it starts??

 

How old is your battery?

 

main relay x2.

listen for the fuel pump when you turn the key.

 

Battery is usually the first thing you should check. Everyone should have one of those rechargable boosters, I must have used mine literally over 100 times.