open loop/closed loop?
 

Can someone please explain what open and closed loop means or does. sorry for the "newb" question guys, I just would like to know.

Are you familiar with what your O2 sensors do? If not, a quick description would be that they measure your exhaust gases and tell your engine control computer what the air fuel ratio current is at. With that info, the engine computer can adjust how much fuel it is adding to the engine (can't do much about how much air is or isn't there) to optimize engine efficiency and emissions.

So, what is "closed-loop" vs "open-loop?" Well, O2 sensors don't function accurately until they get warmed up. This takes a few minutes of run time...especially if your truck has sat overnight. In other words, when you start your cold truck, the engine computer has no acceptible feed-back from your O2 sensors, and it knows this. The only option at that point is to "guestimate" how much fuel to add based on how much air is being measured passing through the Mass Air-Flow Sensor, and what temperature that air is currently at, from the Intake Air Temperature Sensor. This is what is know as "open-loop," because the engine computer has no information given back to it to know if the air/fuel mixture is right or wrong.

Once the O2 sensors reach their operating temperature range, the condition is then know as "closed-loop," because now the engine computer knows for certain if it needs to add more or less fuel.

This is why a vehicles emissions will typically be at their worst when a vehicle is cold. Invent an O2 sensor that works from cold temp to hot temp and you will be a millionaire.

Hope this helps,
Mike

thanks mike,
I kept seeing it referenced on here but never knew what it meant. thanks to you I understand 100% now.:thumbsup:

switch
 

closed loop goes off preset pcm fuel tables-open loop goes of o2 sensor readings fyi:thumbsup:

The PCM runs off predetermined, known good fuel tables when the engine is under open loop, like on cold start up or WOT operation. In closed loop, the PCM adjusts fuel trims based on feedback from the upstream O2 sensors.

The PCM also goes into open loop under heavy acceleration, or when a fault (such as a misfire) has been detected - under hard acceleration, we don't care about emissions, we just don't want to get run over by that tractor trailer we just jumped in front of, so the PCM commands open loop which typically richens things up a bit and disregards the O2s in the sake of maximum power rightaway.

In the case of something like a misfire, the PCM may command open loop operation to protect the engine - more fuel (higher injector pulse width on the working cylinders and/or increased fuel pump duty cycle) is added to help cool the combustion chambers/engine, and to help displace excess oxygen (from the dead cylinder/cylinders) in the exhaust so the converters don't get burnt up.

Lots more good reading at www.fordfuelinjection.com

Very cool to learn it all.

Adrianspeeder