Will I feel much pain if I injure my liver?

Depends on injury. The liver has a capsule covering that contains nerve endings. Either stretch the capsule due to liver enlargement or bleeding, or puncture the capsule due to trauma of any kind, and you have the possibility of considerable discomfort. Infections, infiltrative disease, cirrhosis may not register with a lot of pain but certainly place the liver at risk. Manifestions of end-stage disease can kill.