If you want to drive lowZ injectors without ballast resistors, you want to use PWMing. Since v3.2 the default autoassembled configuration comes with PWMing capability, so this is only needed for formerly ordered v3.1 or v3.0 (or if you let the smoke out of the FETdrivers somehow or you just want to donate 7 Euro :-).
PWMing on v3.0 .. v3.1 requires:

• 2*Rnet (5pin, 2k2..10k) to PWM the FETdriver inputs from the common signal
• 4*MC34151D or compatible MC33151D (each can drive 2 gates: do 2 channels) FETdriver chip
• 8*22..33 Ohm 0805 resistors (for FET gates)

Note that high-voltage flyback will smoke if PWMing is configured (so you make the low voltage flyback if you plan to configure PWMing !), see wiki FlyBack page