By now you probably have a pretty good idea of how far the adjustment needs to go from min to max recommended - if so, probably a quicker way to test (rather than hooking up manometer each time) might be to divide that TOTAL adjustment range into 6 or 8 smaller increments, then go down ONE increment, retry; lather, rinse, repeat. Do NOT go any further than where you remember the lowest setting being.
If you get lucky and it stays lit, I'd go ONE MORE small increment in the same direction and re-try. If all seems good (steady yellow led) I would collect some info with your DMM. (NOT manometer, altho that'd be good to know also) - you STILL should know what DC voltage is on that flame rod when it's actually WORKING, and write that (and pressures) down for future (hopefully more than one day) use.
BTW, too MUCH gas pressure can screw you just as much as too LITTLE, so the scientific method is definitely your friend.
At least you're not trying to do this with NG - it has about one TENTH of the tolerance for flame fuel/air ratio as propane... Steve