As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING BOTH ENGINES AND CALLING FOR TAXI CLEARENCE. THE TOWER INFORMED US THAT THERE WAS GRAYISH SMOKE COMING OUT OF ONE OF THE ENGINES (THEY THOUGHT THE LT SIDE, BUT COULD NOT BE 100 PERCENT CERTAIN) ALL ENGINE PARAMETERS APPEARED NORMAL. REMOVED AND REPLACED LT ENGINE CHECK VALVE IAW MM 71-70-01. OPS AND LEAK CHECKED SATISFACTORY. NO SMOKE NOTED FROM TAIL PIPE.