A319 Captain reported confusion for lack of guidance while manually starting an engine per MEL. Crew received an ENG 2 IGN B FAULT on EICAS and was uncertain as to how to respond due to lack of specific procedures.

Narrative

Operating flight which had an MEL with a start valve fault. This MEL required mx to manually operate the start valve while the flight crew performed the start. This is already outside of normal operations; and there was a lot to consider. I called mx and discussed the issue with them. It was agreed that I would speak with the mechanic that was performing the manual valve opening directly to come up with a plan of attack. We agreed on a plan and a start was performed at the gate on the number 2 engine under very abnormal operations; an MEL was received; and pushback requested. We then discussed the number 1 engine start sequence. This is also abnormal for the airbus due to the number 1 engine being started first and used to single engine taxi per the Flight Manual (FM). The FO and I agreed on what we thought was a proper start sequence and successfully performed a start on number 1. Again; an abnormal situation considering we start and generally taxi out on engine 1. Once we got to ZZZ from ZZZ1 we were assigned to fly to ZZZ2 under the same starting conditions as before only this time when starting the number 2 engine at the gate; we got an ECAM (Electronic Centralized Aircraft Monitor) of ENG 2 IGN B FAULT. This became a very abnormal and perplexing issue due to we were already starting an engine in an abnormal way. This was not a normal FADEC (Full Authority Digital Engine Control) controlled start sequence; and it was not a manual start sequence due to and engine start fault ECAM. At this point; I let the mechanic know we had an ignition fault and the engine isn't starting. Per the supplementary procedures; for manual start valve start; there are NO contingencies for if the engine does not start. I am honestly still questioning if this is considered a manual start per the FM; an automatic start with full FADEC controlled minus the start valve; or its own separate procedure. In any event; the manual start valve procedure in the supplementary procedures in the FM provide no contingencies for if the engine does not start. We had no idea if dry motoring was needed; and if needed; would it be required to have mx open the valve to dry motor; and if that is the case; there is no procedure for dry motoring manual valve operation. Further; the mechanic operating the valve told us to shut the engine down after the ignition b fault; and that we could restart on a. Although this is true; it also states in the MEL that the ignition system must work on the effected engine. Because of the airbus logic; I take this to mean the engine is still mostly a FADEC controlled start because during manual starts and airborne starts; per the FM; the FADEC will use both starters. All this is to say; I don't think this is a clearly written procedure; and I at least have a lot of questions about the safety of the procedure.