You're probably right, not much point in taking the risk to kill him over it unless he ran across something extra crazy. My thought is he either died a normal death or was killed off for some other reason.

I'm glad to hear you're working on a device too! The more people the better! I'll definitely share more info on mine once I test it.

As for making sure the engine doesn't run rich/lean, isn't the idea to let it run slightly lean when the system is in effect? I may be incorrect but I believe I read that increasing the efficiency of the burn by injecting HHO can reduce overall cylinder temperature thus allowing you to lean it out more with less threat of detonation/damage. I have an EGT sensor (installed this last weekend), so I'm basically planning on getting a base reading on the EGTs, add the HHO then see if I get a drop in the EGTs. If I do, I was going to then re-tune and lean it out as much as possible while keeping an eye on the EGTs to ensure they don't rise above that base reading. While of course also monitoring for a loss in power.

I will be injecting the HHO through the intake as you said, basically on the main intake tube right before the throttle body. Also rather than a tuneable EFI inline (would be ideal for most vehicles), I actually have a complete custom ECU (megasquirt).

One more note that's somewhat unrelated. Prior to putting this HHO cell on my car I was experimenting with using it to run (well attempt to run) a small single cylinder engine, like one off an old edger. Primary issue was it was set up for wasted spark and the timing is slightly off for pure HHO so when I inject the gas (no normal gasoline, only HHO), it basically kicks back instantly and shoots a flame out the side. I haven't had time to completely redesign a timing system for it, but with the force of the kickback it makes me think that if the timing were correct it'd actually run, and that's solely off just hydrogen.