When a car is cold and or starting up, why does it have to be in open loop mode? I understand it's to "protect" it but I'm not really sure what that means either. How exactly is running in open loop going to protect a car? I've found most issues with a car are due to overly rich mixtures leaving carbon deposits. A lean misfire shouldn't damage the engine and detonation would be hugely unlikely considering the engine is cold.

 

Closed loop is feedback from the A/F or O2 sensor to trim the fuel mixture however the A/F or O2 sensor needs to be hot for it to read properly. Engine ignores the sensor while it is heating up.

Develop a better sensor that doesn't need to warm up and it can be in closed loop all the time.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by stumpyf4 &raquo;</TD></TR><TR><TD CLASS="quote">Develop a better sensor that doesn't need to warm up and it can be in closed loop all the time. </TD></TR></TABLE>

It's not that simple. Modern electrically heated O2 sensors heat up pretty quickly, but also keep in mind that engines run in open loop not only when the engine is cold, but also at lower rpm and at lesser throttle openings, i.e. when you open the throttle wider than X or when the engine revs higher than Y then engine runs in open loop with no influence from the O2 sensor.

Check this page:
http://www.moto-one.com.au/per....html

This is a bike site but it has a pretty good explanation of open / closed loop etc.

 

Let me explain Closed and Open Loop.

Open loop is when a majority of the engines sensors are not within "normal" operating range. Most codes are thrown once the engine fully warms up, and the PCM can determine an error based off of information from the others. The obvious catch is a wire and/or complete sensor failure, that is an automatic pre-start fail. The PCM will inject fuel based on a preset table in its ROM based on the airflow received. In essence, most sensors are ignored at this point. Open loop is acheived from -100F to around 160F (engine temp) Idle, and WOT. (WOT has its own table, and is always an open loop operation)

Closed loop is a mode where the engine can make precise adjustments using all of its sensors for best economy. It will use the MAP, IAT, CTS, HO2S, KS, TPS, and RPM to determine the right amount of fuel to deliver. This involves a rich/lean switch that happens many times per second. This mode is only achieved with a steady throttle, and a fully warm engine 160-210F. Most older cars will never come out of open loop with a bad coolant sensor, but newer cars use the IAT, and other temp sensors to make a "guestimation"

Open loop is a failsafe, if the engine timed everything off of what the sensors said, when one fails your car could suffer some huge problems, like with a weak fuel pump. Low fuel pressure, high injector pulse, very lean, will set code P0171, and default to preset fuel trims for safety. You could burn up a piston, throw a rod, (say if KS failed) and many others.

 

^ More or less my understanding.

When driving at cruising rpm with a relatively small and steady throttle opening the engine will be in closed loop most of the time, but when driving around town with much more varied throttle openings and rising / falling rpm the engine will run in open loop a lot more and closed loop a lot less.


Modified by johnlear at 10:45 PM 7/24/2008

 

I am trying to learn about Open and closed loop and basically when a car like a honda is cold this means that it requires more fuel to inject on a cold motor and when the engine warms up to the right temperature the idle will go down to the right rpm which will be in closed loop mode is this correct? Also also when you are in wide open throttle saying your racing somebody or doing something with (WOT) it will be in open loop mode due to the engine injecting more fuel to the motor in a more rich fuel based setting that you would see on a wideband is this correct?

 

it will be in open loop because the factory o2 sensor cannot distinguish anything other 14.7 afr, which is not optional under WOT conditions.

 

Now what if you are running an AEM Wideband would it be in open loop all the time like a factory o2 sensor? And also is a factory o2 sensor a narrowband sensor and would a aem wideband o2 sensor which I think is Bosch be a narrowband o2 sensor as well?

 

AEM wideband is a wideband 02 sensor