I am assuming you have a nissan k-21 or k-25 engine with a Nikki Converter. If you already changed the injector, I would suggest taking a pressure reading of the converter. It should be about 4.5 psi, if it is a steady low reading and you hear gas leaking you may have an open relief valve in the injector housing behind the main injector. The assistant injector can also act as a relief valve if pressure is sufficient to overcome spring pressure. If you disconnect the balance line from the converter and you have an lp leak your converter is leaking internally. I am not sure you can get the parts to service the converter as Cat has it as a non-serviceable item. LP problems don't always set a code so the best bet is the pressure reading at the converter.