Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 211; Flight Crew Total 957; Flight Crew Type 313
Other / Unknown; Troubleshooting
Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Flight Crew Landed in Emergency Condition
Aircraft
A Cessna 150K departed ZZZ1 piloted by an instructor and student after performing a checklist backed thorough preflight check. We flew cross country to ZZZ and ZZZ2 performing touch and go landings. On our last leg from ZZZ1 to ZZZ1 we flew west of downtown Chicago underneath the ZZZ class Bravo 1900 ft. shelf. Somewhere due East of ZZZ; the aircraft engine attempted to fail and we lost altitude from 1600 ft. MSL to 1400 ft. MSL. After playing with the throttle; the engine came back to full power and we continued on to ZZZ1. Between 3-5 miles possible from ZZZ1; the engine began to fail again. All fuel items were on and rich. Playing with the throttle did nothing this time and knowing about our altitude; I made the decision to make a 180 degree turn into the golf course where a forced landing without engine power was executed. Nothing and no one was damaged or injured and a safe landing was made. The fuel level in the right tank was indicating a quarter and the left was indicating just above empty. Upon exiting the aircraft; we noticed the left fuel cap had somehow gotten disconnected from the fuel tank neck and was being held on by its chain. All flight planning fuel burn items indicated landing with 7.4 gallons of fuel left at ZZZ1.
C150 Instructor pilot reported fuel cap came off with loss of fuel; resulting in an off airport landing.