Ok, so i was riding with my girlfreind on the highway in her 94 3.8 Thunderbird LX. The cars shifter lights are broken so it can be difficult to tell what gear it is in. For about 10 minuits she was going 60+ on the highway in 2nd gear. Ever seince this incident, her engine has been makeing a distinct knocking noise, espcially when accelerating. Whats going on?