If this is a warm restart problem, fuel pressure could be leaking down when the engine is off. Could be at the injectors (one or more leaking) or at the pressure regulator or the fuel pump module.
Have a tech do a static pressure test with the engine off (or get a gauge and do it your self)
Pressure should not be less than spec after a certain time. You'll find that in a manual here ....
http://www.lunghd.com/Downloads_and_Links/Downloads.htm
It is normal for the pressure to go to 0 when the engine cools down. Just let the key sit in the run position for 1-2 seconds before moving to the crank position.
JD