What was found
APU WILL NOT START. ACFT GROUNDED. VERIFIED CDS REPORTS FCU RESOLVER CIRCUIT SHOWS OPEN. REMOVED AND REPLACED APU FCU IAW AMM 49-31-11/401. FAULT CODE CLEAR. STILL APU WILL NOT START, NO FLAME SHUTDOWN. NO NOISE FROM THE IGNITER PLUG DURING APU START NOTED. COMPLIED WITH FIM 49-40, TASK 802. REMOVED AND REPLACED IGNITER PLUG, IGNITER LEAD, AND IGNITION UNIT IAW AMM 49-41-51, 49-41-52, AND 49-41-31. GROUND VERIFICATION SUCCESSFUL IAW AMM 49-11-00. RAN APU 3 TIMES. NO DEFECTS NOTED. NO FAULTS FOUND.