Starts up fine when cold.
After it warms up to normal operating temperature by idling it, difficult to start.
If driven hard (temp higher than the above) impossible to start.

When driving in hot weather or when driving hard, may shut off and impossible to start until cools down.

I've checked a number of things including fuel pressure, coils, ignition switch and other electrical--all these items check out.

So, I'm thinking bad compression.

Sound about right?

 

Do a compression test to be sure.

 

I thought compression improved when hot.
Your problem sounds more like vapor lock...but I'm no expert.

 

I do believe it is the opposite. Because the intake and combustion chambers are cold, when cool air comes in it is as cold as possible, therefore more dense. As the car warms, the air is less dense therefore greater compression is required.

If the car is right on the edge of "just enough compression", this slight decrease in compression efficiency can cause hard starting.

Or such is my understanding, at least.

 

What's your fuel setup?

Do you have enough fuel pressure when stopped (leakdown from pump and pressure regulator)?

Heat might be a problem for your fuel rails if you switched over to a returnless system.

 

Stock with an upgraded fuel pump, bigger injectors and an aftermarket fuel regulator.

 

compression drops when hot, everything has expanded


its simple thermal dynamic expansion eh