this injector is indeed PWM (pulse wavelength modulated) and has an "assistant" injector right next to it in the throttle body. however if you hear gas even after the motor is turned off then you may have a bad LPG lock off valve (this unit's schematics may call it an LPG interceptor valve) which is located in the LPG lines before the 2 stage regulator.
there is on some of these trucks an LPG injector "Driver" box that is mounted inside the engine compartment right near the ECM
code f02 is from a low battery voltage condition
I would suggest that you start with "check-replace" of the relays in the box next to the fuse box, and be sure of the battery voltage and Alt output, as low voltage when running can set all sorts of weird codes.