a couple observations on your firmware....
max extruder temp setting should be set to 295 to take over run into account - going over 300 will damage the thermistor.
#define HEATER_0_MAXTEMP 310 //{SD Patch}
your endstop settings:
// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR 1
mine are:
// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR 1
#define Y_HOME_DIR 1
#define Z_HOME_DIR -1
My printer is also an SD4 running on a Rumba and an E3D v6 hotend.
If you don't have one, I highly recommend an 8825 stepper driver for the extruder - much nicer than a 4988 with the E3D.
SD4 #1 & #2 - Lawsy carriages, E3D v6, Rumba controller board, mirror bed plate, X motor fan, upgraded PSU & Mica bed heater
SD4 #3 - in the works ~ Folgertech FT-5, rev 1
Printit Industries Beta Tester - Horizon H1