Can anyone tell me exactly what open and closed loop are? This may sound like a dumb question, but I can't find it on the FAQ thread and a newby like me needs to know.

 

closed loop is when the pcm is reading what sensors are saying and adjusting accordingly. open loop is when its going by a given set of setting until the sensors warm up enought to switch to closed loop.
some like to run open loop tunes so your not fighting the o2 sensors. i did this on mine when i went to a big cam and it ran much better then it did in closed loop.

http://para.noid.org/~lj/


thats has a good write up on the lt1 pcm.

 

closed loop usually = the ghey... id like to have a open loop tune. Most of your problems you find will happen in closed loop and youll have to search around testing **** to find out what sensor it is

 

Why not just run a carb then?

I thought the entire point of closed loop was to have good part-throttle response where the PCM would actually do some form of short and long-term fuel trim modification depending on environmental factors.

EDIT -- my GM847 car runs in closed loop, but I do have to address some tuning issues to avoid a false misfire code.