open loop is when the engine is not using feeback to regulate fuel. There are parameters that need to be met before the ECU will regulate and control the fuelling in real time
Usually the most important things are engine tempurature and if the O2 sensor has come up to tempurature. There are others dependant on the vehicle. Throttle position, RPM, boost pressure etc, things like this will determine if its in cloose loop or open loop. These can be changed on aftermarket tuning solutions.
The big thing is weather its in fuel control or not. Simple to think about is if its warmed up fully or not? and if you are hard on the throttle or not.
Simply put, if the engine is warm and you are cruising or mildly accelerating, its in fuel control (or closed loop) If the engine is cold or you are ripping on it, its most likely in open loop and not in fuel control.
when the "loop" is closed,the engine recieves signals from its sensors to determine the correct amount of fuel and ignition timing to apply. It reads throttle position, manifold vacuum, crank sensor etc and determines how much fuel is needed. It knows that for that much fuel it needs to open the injector(s) for a certain amount of time, measured in miliseconds. it then does this. It then reads those same sensors again, and checks to see if its targets were met.
This all happens many times per second and constantly.
When its not in fuel control, or the "loop" is open, the ECU just looks in its built in tables and regulates the fuel injector duty cycle from there. It works, but its not as accurate and its not real time.
Over time, the engine will know that it always needs a bit more or a bit less fuel in that area of the fuel map, so it adds or takes that out so that it doesn't have to worry about that part. These are called fuel trims. It trims the fuel tables out for those areas of the map. Over time the conditions will change. IE:atmospheric pressure, air tempurature, humidity etc, so it may need to make adjustments to the tables again.
Long term, the engine itself will change due to wear. Again the ECU will take this into account.
its more complicated than this, but this is the basic idea.
Usually the most important things are engine tempurature and if the O2 sensor has come up to tempurature. There are others dependant on the vehicle. Throttle position, RPM, boost pressure etc, things like this will determine if its in cloose loop or open loop. These can be changed on aftermarket tuning solutions.
The big thing is weather its in fuel control or not. Simple to think about is if its warmed up fully or not? and if you are hard on the throttle or not.
Simply put, if the engine is warm and you are cruising or mildly accelerating, its in fuel control (or closed loop) If the engine is cold or you are ripping on it, its most likely in open loop and not in fuel control.
when the "loop" is closed,the engine recieves signals from its sensors to determine the correct amount of fuel and ignition timing to apply. It reads throttle position, manifold vacuum, crank sensor etc and determines how much fuel is needed. It knows that for that much fuel it needs to open the injector(s) for a certain amount of time, measured in miliseconds. it then does this. It then reads those same sensors again, and checks to see if its targets were met.
This all happens many times per second and constantly.
When its not in fuel control, or the "loop" is open, the ECU just looks in its built in tables and regulates the fuel injector duty cycle from there. It works, but its not as accurate and its not real time.
Over time, the engine will know that it always needs a bit more or a bit less fuel in that area of the fuel map, so it adds or takes that out so that it doesn't have to worry about that part. These are called fuel trims. It trims the fuel tables out for those areas of the map. Over time the conditions will change. IE:atmospheric pressure, air tempurature, humidity etc, so it may need to make adjustments to the tables again.
Long term, the engine itself will change due to wear. Again the ECU will take this into account.
its more complicated than this, but this is the basic idea.
