You need top determine if you are losing spark or fuel when the engine will not start. Check for fuel pressure (you will need a fuel pressure gauge and look the specified fuel pressure for your vehicle). Remove the fuel hose that goes to the fuel rail and get a friend to crank over the engine to see you have adequate fuel volume (you should have approximately 1 pint of gasoline in ten seconds of cranking). Next "listen" to the fuel injector. Using a mechanic's stethoscope (or use a long screw driver placing the handle end up to your ear place the metal tip end of the screwdriver against the body of the fuel injector), get a friend to crank over the engine while you "listen" to the fuel injector listen to each injector at the same point of the injector body. You should hear click, click, click as the injector is electrically opened and closed by the computer, if the injector is not being triggered you will not have fuel getting into the engines cylinders. Disconnect the electrical connector at the fuel injector with the ignition key in the "on" position, (next position after the accessory position) you should have 12 volts at one of the two wires at the injector. This true for most vehicles but you need to consult a workshop manual for your vehicle to see that this is true for your vehicle. When the engine is running the second wire at the injector gets grounded by the computer in your vehicle many times a second controlling exactly when and how much fuel gets injected into the engine. Remove a sparrk plug wire get a friend to crank over the engine and see if the ignition system is supplying spark to the spark plug.