As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: IT WAS A STRONG SMELL OF EXHAUST. IT WAS DURING TAXI BACK TO THE GATE. IT WAS NOT DURING THE TAXI OUT. THE SMELL LASTED ABOUT 5 TO 10 MINUTES BEFORE WE SHUT DOWN THE ENGINES. THE AIR CONDITIONING SYSTEM WAS CONFIGURED WITH A BLEED OFF AND THE APU AIR BLEED ON DUE TO COMPLIANCE WITH AN MEL 30-03B. **SUPPLEMENTAL REPORT WILL BE SUBMITTED**(OPEN).