As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING BOTH ENGS WITH THE APU STILL RUNNING SMOKE FILLED THE COCKPIT & CABIN. CABIN EVACUATED ONTO RAMP, EMER DECLARED. PERFORMED TROUBLESHOOTING IAW FIM TASK 21-22-00-810-806-A01 & FOUND THE LT PACK TO BE AT FAULT. R & R ACM IAW AMM 21-51-08. OPERATIONS CHECKED GOOD.