my 3.1L will start good when the engine is ambient temperature. however, after it has been driven, the engine is warmed up, and i turn it off and try to restart it........it starts really hard. it always starts, but i have to crank on it for 5 seconds (or longer sometimes) to get to stay running. a friend suggested to replace the fuel pressure regulator, but that did not change a thing. does anyone have a suggestion?

3.1L J-body? What make & model is that?

Not sure but if it also idles roughly once it's warmed up, then consider replacing the coolant temperature sensor (not the thermostat). If the sensor operates out of spec and tells the computer that the engine (coolant) is colder than it actually is, then the computer will feed a too-rich fuel mixture to the engine (which is the equivalent of turning on the choke). That's fine when the engine is cold, but not when it's warmed up.

As said we need the specific car information.Year,model and we know the engine.I would not go as to far to say coil packs.They could create the hard start when Hot.