Just a suggestion but the oil consumption run would be a way of determining this fault, of course running up to 4 engines at power can be impractical and costly so some idea from oil uplifts should narrow the field, older cold air units with oil sumps can produce this problem and the APU has to be eliminated but usually this smell occurs during take off and early climb out. Even the quad B744 will need an opposite balancing engine when power is applied.