7HGFAD-2141J Onan Generator popping!

Hi all, have this truck mounted generator that is popping some, I'm told it died at least once. It has had fairly good maintenance, recent oil change, just put in new plugs, fuel filter was changed and is clear. Once thing I did notice is when priming the fuel it will go up to about 45 psi (not running) and will then drop off quickly when you let up on the primer....should this thing hold pressure like most cars? Also when it is running under a load, the fuel pressure gage needle will bounce from 30 to about 50 psi...not sure if it should do that. spec says fuel pressure is 43 psi....I have had it running for a while. the only code was an ac no signal code (27 code), but I am guessing that is from when it died the one time.

Thanks in advance.