Years ago, I tried that on a Sable wagon. Instead of connecting my HHO to the alternator, I hooked it up to two trolling/RV batteries. I also made a poor man's O2 sensor modification by putting about 0.1-0.2V bias to make the engine run leaner Also tried the oil anti fowler for sparkplugs on the O2 sensor. NO DIFFERENCE FOUND. A TOTAL WASTE OF TIME. I thought using the batteries, would make a poor man's hybrid, but HHO did not work at all.
