Irvine-based Quantum Fuel Systems Technologies Worldwide Inc., a maker of fuel system parts for hydrogen vehicles, has hired an adviser to look at possibly selling its Tecstar Automotive Group unit. Quantum said Thursday it hired Merriman Curhan Ford to look at finding an investor for Tecstar or selling part of all of the unit, which builds custom vehicles for General Motors Corp. and other automakers. The unit made up 88% of Quantum's $36 million in first-quarter revenue. Tecstar had an operating loss of $3.4 million in the period. The company said it doesn't have a timetable for a possible sale or investment.