As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BLOCK TURNBACK. FLIGHT CREW REPORTED LOW PRESSURE BOTH ENGINES DURING START WITH FUMES INTO CABIN. REPLACED BMC NR1. LOW BLEED PRESSURE OPS CHECKED GOOD IAW AMM 36-11-34, PAGE 401. FOUND DE-ICE FLUID IN APU AIR INTAKE WHICH WAS CAUSING FUMES. CLEANED APU AIR INTAKE. NO FUMES NOTED IAW AMM 49-16-00-100-003.