What was found
ENG 1 BLEED LEAK IN FLIGHT, FL280 FOLLOWED QRM PROCEDURES, AND UNABLE TO MAINTAIN CABIN PRESSURE DUE TO PACK 2 MEL. RETURN TO ORD EMERGENCY DECLARED/NO OVERWEIGHT LANDING/NO MASK DEPLOYMENT. T/S AML 5133549, FOUND E1 PRECOOLER LEAK AT TOP OF OUTLET DUCT. REMOVED AND REPLACED #1 ENGINE PRECOOLER IAW ERJ170 AMM 36-11-08 OPS TEST GOOD.