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Old 04-22-2004, 12:26 PM   #1
FuJi K
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Default Close loop, open loop? it means....

What does close lopp and open loop mean? Air fuel ratio? Tuning with each? It's effects?

Thanks!
FuJi

p.s. Yes, a #3000 member asking this question....
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Old 04-22-2004, 12:46 PM   #2
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When the engine is running in closed loop, it is using the A/F signal from the 02 sensor to regulate the mixture. There is a feedback "loop" between the sensor and ECU so the ECU continuously makes adjustments based on the 02 data.
In open loop the 02 sensor isn't used and the ECU sets mixture based on stored maps and other sensors (coolant temp etc).
Usually open loop is used on initial start and during warmup, until the 02 sensor reaches its operating temperature and produces a signal and the engine also reaches its operating temp, at which point the switch to closed loop takes place.
Under heavy acceleration the system will generally go open loop (some vehicles may remain in closed loop).
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Old 04-22-2004, 02:37 PM   #3
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good info
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Old 04-22-2004, 04:32 PM   #4
loreley
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what about the effects of having a closed versus open system? i think thats what the original poster was getting at
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Old 04-22-2004, 07:19 PM   #5
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All cars come with a closed-loop system from the factory because it's the only way they can pass emissions. By constantly monitoring the A/F ratio during normal operation, they can keep emissions to a minimum and also achieve good fuel economy.

The problem is that the narrow-band O2 sensors they rely on don't react fast enough for wide-open throttle conditions and the computer wouldn't be able to react fast enough to keep the motor alive under full throttle. So past a certain throttle position, they switch to open loop and use fixed look-up tables. Those tables are usually set on the rich side, especially on turbo cars, to prevent detonation, which leads to expensive warranty repairs on pistons with holes in them.

You can get aftermarket systems that only run open loop, but they'll never be as smooth or streetable as a system that includes an open-loop mode. Because they never have a big enough map to handle all the different possible conditions the motor can encounter. But on a race car that only ever sees full throttle, that's not a big issue.
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Old 08-12-2014, 06:12 PM   #6
bluesguyej25
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I have a code scanner that can monitor the fuel system for my 08 2.5i, and during live data it is showing ol -fault. Do you think that it is not sensing the ol and running in limp mode? I don't have a header. I had it tuned 3 months ago open source rr. And I cannot clear the code. Purchased a new up stream o2 sensor to no avail. Suggestions?
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Old 08-12-2014, 08:06 PM   #7
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Quote:
Originally Posted by bluesguyej25 View Post
I have a code scanner that can monitor the fuel system for my 08 2.5i, and during live data it is showing ol -fault. Do you think that it is not sensing the ol and running in limp mode? I don't have a header. I had it tuned 3 months ago open source rr. And I cannot clear the code. Purchased a new up stream o2 sensor to no avail. Suggestions?
I'll fire up my Delorean and go back to 2004 to let Chuck know.
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Old 08-12-2014, 08:44 PM   #8
lemming
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It would be much more useful if you posted the actual DTC (P0-whatever) it is throwing.
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Old 08-12-2014, 08:59 PM   #9
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Quote:
Originally Posted by bluesguyej25 View Post
I have a code scanner that can monitor the fuel system for my 08 2.5i, and during live data it is showing ol -fault. Do you think that it is not sensing the ol and running in limp mode? I don't have a header. I had it tuned 3 months ago open source rr. And I cannot clear the code. Purchased a new up stream o2 sensor to no avail. Suggestions?

Maybe contact the tuner (from 3 months ago).
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