What does open loop and closed loop mean?
Open and closed loop refers to whether a feedback mechanism is included in the controller-motor assembly for the controller to verify that the motor is actually moving as expected by the command. In open loop, there is no feedback, so a command will vary the controller’s output to the motors, but the actual speed will depend on the friction, slope, load and the presence of obstacles. In speed closed loop, the controller will measure the actual motor speed and adjust the command accordingly. In position closed loop, the controller will measure the angular position of the motor’s axle and move the motor until the desired position is reached. The AX2550 supports all three modes described here.
Closed Loop (CL) refers to a control sub system in the PCM that allows the engine computer to make adjustments to idle and part-throttle fueling based on feedback from the narrow-band oxygen sensors. This makes fueling more consistent (in most cases) and helps with highway economy and general drivability. Open Loop (OL) operation means that fueling is calculated and metered from the MAF (unless in speed density where no MAF is used) and other static tables alone. OL is sometimes desirable in instances such as aiding the operation of a very large camshaft with lots of overlap at lower RPMs. This overlap allows fresh air to escape into the exhaust which “fools” the factory oxygen sensors into thinking that the engine is lean. This can have the effect of causing over fueling at these low RPMs as the PCM attempts to correct a scenario which it perceives to be lean.
