VCM Defination
Variable Cylinder Management (VCM) is Honda's term for its variable displacement technology, which saves fuel by using the i-VTEC system to disable one bank of cylinders during specific driving conditions—for example, highway driving.
Sounds so nice, but while these 3 cylinders in bank 1 are disabled by closing their valves, fuel ingection via pressurized oil valves mechinism, these 3 cylinders' pistons themselves are still in physical up and down motions with Bank 2, thus a vacuum is formed inside each of them, as piston rings worn out along time, oil is sucked in and burned with gas. This will finally foul the spark plugs and kill the CAT, engine performs worse but consume more gas, there are vibration issue on engine mounts as well and other side-effects.
Below are my old spark plugs from both banks, (2006 Honda V6, engine 280k KM, plugs 140K Km)
cylinder#1 (the worst among all 6, oily and irridium electrod burned, oil is burned in #1 for sure )
cylinder#2 (lost focus, but better than 1 and 3)
cylinder#3
cylinder#456 (no VCM side, looks much better to bank1, worn but dry)
