I've been experimenting with HHO units for about two years now with little success.

Vehicle 1992 Jeep Cherokee 4.0L I-6 automatic.

Anyone have time with this engine?

My DD service vehicle driven on the same route and roads 5 days a week.

Some background to help the help.
Engine was checked and rechecked to be in the best running order possible.
Recalibrated and/or replaced all sensors as required.
Confirmed fuel system to be calibrated and remanufactured Bosch injectors installed.
Replaced cat and muffler with Magnaflo performance replacements.
Installed a narrow band AFR gauge on its own O2 sensor.
Installed an EFIE and MAP adjuster.
Factory PCM no changes to program.

Ran the vehicle for a year to ensure base mileage was repeatable and all systems maximized.
15-17 MPG depending on ambient temperature and driving conditions.

Started with a home built wet cell that produced approx 1.5 l/min
Nothing to report.
Upgraded to a larger 2-3 l/min dry cell
Nothing to report.
Upgraded to a larger 5 l/min dry cell
Cell pulling 20amps with 6TBLS/gal, output fed to air intake just in front of the throttle body.
Finally started to see a change in AFR and adjusted the EFIE to keep indicated AFR to normal.

After 300 miles of driving I experienced ZERO change in economy and then blew up the 45amp PWM,
There is a little SOTP power change but not to justify the 1000 bucks I have invested in this project.

I'm feeling the pain of Thomas Edison, just not sure I can finance another 3500 tries. This aint a light blub.