Is this as a response to a possible fault condition or part of normal operation?

(At first thought seems a bit bizarre introducing extra fuel at irregular parts of the fueling cycle as part of normal operation )

I am getting faults for low fuel pressure but have not been able to "Catch it in the Act". There is no evidence of metel fileings/Crap in the fuel filter. Owner is tepted to try fitting a new pressure regulator but it is quite expensive and I am wanting to eliminate less expensive possibilities before going down that route.