Method 1: Impact wrench
Method 2: Breaker bar and socket on balancer bolt. Rest breaker bar on something solid (subframe, etc) toward front of car. Disable ignition (pull coil wire). Crank engine. Bolt will come loose. Done this many times with great success.
Even with plugs in, a wrench on the bolt will turn the engine over before the bolt breaks free.
05 Taurus SEL Duratec - my daily driver
04 Taurus SES Duratec - wifes car
95 Taurus GL Vulcan winter car
Toy #1 - 86 Tbird 5.0 (original owner) - LOTS of mods
Toy #2 - 88 Tbird Turbo Coupe - LOTS of mods
02 Pontiac Grand Prix GT
67 Honda 450 Super Sport - completely customized