Luke,closed loop is when the car will run at lambda 1 which is perfect fuelling at cruising speeds,air fuel ratio reading 14:7:1.It's standard on late sapps green stickered L8 and the escos p8 ecus,If you go onto motorsport developments website,take a look at the closed loop article that Stu has written,it will all be explained there for you.I hope this helps.

Thanks.Lee.