Can someone just clear up the differense of open and closed loop for me? whats it all mean?

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1985 IROC-Z, nuff said :P

 

In short, Closed loop means that the ecm (computer) is looking at the Oxygen Sensor values and adjusting the fuel accordinly to maintain the stoich. 14.7:1 air/fuel ratio. When in Open loop it does not look at the Oxygen sensor and uses predetermined values.

 

I see...

So if i was to some how keep the car in open loop and just run it off of predetermined values theoretically I could get the *best* performance assuming it was tuned right?

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1985 IROC-Z, nuff said :P

 

Actually at wide open throttle the ecm automatically goes into open loop. This is how you are able to get good gas mileage while driving under normal conditions in closed loop with the ecm looking at the oxygen sensor, while also being able use predetermined tables (so as not to go lean) in open loop while at wide open throttle.

It uses the throttle position sensor to determine this. Another reason why it is important to have a properly adjusted and working TPS. This is why you are able to tune the amount of fuel (to a certain point) at wide open throttle with an adjustable fuel pressure regulator.

If the ecm where to try to read the oxygen sensor (and adjust the air/fuel ratio to 14.7:1) at wide open throttle you would run lean and damage your engine. There are the linear (aka.. wide band) oxygen sensors which can accurately read richer (ie.. 12.0:1) air/fuel ratios but that is a whole different topic, and your car doesn't have one.

[This message has been edited by TunedPort350 (edited April 30, 2001).]