What was found
AFTER APU SURGE VALVE REPLACEMENT, APU PNEU DURING ENGINE START MARGINAL. BEFORE START 33 PSI AND DURING ENGINE START, APU PNEU MAINTAINED APPROX 24 PSI AND MAX N2 WAS 27. AT 50 DEG F. CURRENT PNEU SUPPLY WILL PROBABLY BE WEAK IN DEN AND OKAY IN SFO. SUGGEST TO RPLACE IGV TO TRY TO IMPROVE PNEU SUPPLY. A GOOD APU WILL NORMALLY BE ABLE TO MOTOR AN ENG TO 28-31 N2 WHILE MAINTAINING APU PNEU AT 29-30 PSI. REPLACED APU IGV ACTUATOR PER MM. LEAK AND OPS CHECKED GOOD.