paul b . my tho9ught process is the pilot injection is earlier than the main shot, and with stock injectors not a big deal. As injector size increases, so does the amount of fuel in this pilot shot. The pilot being early, now has more energy being released while the piston is still traveling upwards. Even if the pilot is 3 degrees before the main event the subsequent battle is heard as a rattle. At least this is my thinking, I have no idea how much earlier the pilot shot is. Other ideas of being able to fire the injectors longer also come to mind, not "using up all the electrical energy" by a wastefull pilot shot. MTBF should go up as well, one less event of open close for the solenoid.