As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON PICKING UP AIRCRAFT IN DTW, THERE WAS A STRONG EXHAUST TYPE SMELL THROUGHOUT ENTIRE AIRCRAFT. THIS WAS WITH NO EXTERNAL AIR AND APU WAS OFF. ODOR LESSENED DURING OPERATIONAL CHECK WITH PACKS ON BUT DID NOT GO AWAY. CREW MEMBERS REPORTED HEADACHES AND NAUSEA. MAINTENANCE FOUND FORWARD OVEN CREATING A BURNT SMELL - REPLACED OVEN AND ACCOMPLISHED BURN OUT WITH NO FURTHER SMELLS NOTED.