closed loop/open loop
Pro
Joined: Jan 2005
Posts: 686
Likes: 62
From: San Jose Ca
Open loop is where the ECM calculates the fueling based on various sensor inputs. Closed loop is the same but thing except that the ECM monitors the end result via the o2 sensor and trims the calculated fueling acordingly. The o2 sensor doesn't send meaningful information until it reaches opperating temp. Only then will the ECM attempt closed loop. Single wire o2 sensors rely on exhaust heat to get them up to temp. This can take a long time or never happen if you've got headers and the o2 is located far enough down stream that it doesn't get enough heat. A heated o2 sensor is one that has a heating element in it (supplied by 12v) that allows it to reach opperating temp quickly. The benefit is that the ECM will enter closed loop sooner with the heated sensor. 
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
The "old" single wire O2's didn't have a built in heater. The heater helps the O2 come up to operating temp faster.
Soem people put long tube headers on, where the collector/O2 is too far down stream of the exhaust port,.... collector is cooling to fast. In this case, the heated O2 is needed to get the ECM to CLoop.
In OLoop,.. the ECM is not monitoring the O2/knock sensor. It operates on preset #'s.
In CLoop,.. the ECM monitors the O2/knock sensor, and adjusts fuel/timing/solenoids/,... accordingly.
Soem people put long tube headers on, where the collector/O2 is too far down stream of the exhaust port,.... collector is cooling to fast. In this case, the heated O2 is needed to get the ECM to CLoop.
In OLoop,.. the ECM is not monitoring the O2/knock sensor. It operates on preset #'s.
In CLoop,.. the ECM monitors the O2/knock sensor, and adjusts fuel/timing/solenoids/,... accordingly.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Open loop is before the O2 reaches it's "light off" temperature, and is able to send meaningful information to the ECM. In open loop, the engine runs off a set of preprogrammed values. Closed loop is after the O2 becomes functional. The ECM "reads" the information coming from the O2 and adjusts the pulses of the injectors for the proper A/F ratio, as reported back by the O2. It's a circle: O2 > ECM > injectors > O2. In other words, a "closed loop".
The O2 must reach a temperature of approx 600*F in order to send usable info to the ECM. If the O2 has been relocated or warms up too slowly the "12v feed" powers a heater to help get the O2 up to and maintain operating temp.
RACE ON!!!
The O2 must reach a temperature of approx 600*F in order to send usable info to the ECM. If the O2 has been relocated or warms up too slowly the "12v feed" powers a heater to help get the O2 up to and maintain operating temp.
RACE ON!!!
Team Owner
Joined: Sep 2001
Posts: 62,067
Likes: 1,723
From: Athens AL
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In closed loop, which begins when the ECMs startup timers have passed AND when the O2 reaches 350 C, the computer reads the O2 sensor.
In open loop, which is just after startup, the ECM ignores the readings from the O2, because its reading is unreliable until it reaches that temperature of 350.
A heated version has a ceramic heating element in it that allows it to work at 200 C and prevents it from cooling off.
In open loop, which is just after startup, the ECM ignores the readings from the O2, because its reading is unreliable until it reaches that temperature of 350.
A heated version has a ceramic heating element in it that allows it to work at 200 C and prevents it from cooling off.
Team Owner
Joined: Mar 2000
Posts: 83,381
Likes: 87
From: Boston, MA
On your 84 it is all timer based, the ECM has no clue what temp the O2 sensor is at.
There are 3 times in the ECM
Cold O2 Start
Warm O2 Start
Hot O2 Start
They refernce a coolant temp at startup and depending on which range the temp falls into uses the # of seconds defined by those start up fields.
There are 3 times in the ECM
Cold O2 Start
Warm O2 Start
Hot O2 Start
They refernce a coolant temp at startup and depending on which range the temp falls into uses the # of seconds defined by those start up fields.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by scorp508
On your 84 it is all timer based, the ECM has no clue what temp the O2 sensor is at.
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by scorp508
On your 84 it is all timer based, the ECM has no clue what temp the O2 sensor is at.
RACE ON!!!
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
Originally Posted by CFI-EFI
Open loop is before the O2 reaches it's "light off" temperature, and is able to send meaningful information to the ECM. In open loop, the engine runs off a set of preprogrammed values. Closed loop is after the O2 becomes functional. The ECM "reads" the information coming from the O2 and adjusts the pulses of the injectors for the proper A/F ratio, as reported back by the O2. It's a circle: O2 > ECM > injectors > O2. In other words, a "closed loop".
The O2 must reach a temperature of approx 600*F in order to send usable info to the ECM. If the O2 has been relocated or warms up too slowly the "12v feed" powers a heater to help get the O2 up to and maintain operating temp.
RACE ON!!!
The O2 must reach a temperature of approx 600*F in order to send usable info to the ECM. If the O2 has been relocated or warms up too slowly the "12v feed" powers a heater to help get the O2 up to and maintain operating temp.
RACE ON!!!
This concept has always been a little "gray" for me... until now. This has got to be one of the best explanations of the concept that *I* have ever read.
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Originally Posted by CFI-EFI
Are you sure of that? Back to my manual. BUT, no C4 has an O2 temp sensor to the ECM. I thought it was necessary for the O2 to come up to temp to provide useful data.
it should also be noted that even when everything's warmed up, the system can tempoararily go back into open loop during sudden transients, such as going into fuel enrichment when slamming on the hammer.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by tempest
O2 has to come to temp as you say, but it is done mainly by "waiting" via timers for the sensor to warm up.
"The sensor is like an open circuit and produces no voltage when it is below about 360*C (600*F). An open sensor circuit or cold sensor causes open loop operation"
One reason I don't buy the "but it is done mainly by "waiting" via timers for the sensor to warm up" theory, is that the timers would require a warm engine to "wait" for the timers as long if it were cold, and delay closed loop when the engine is otherwise ready. I don't think the EPA would sign off on THAT one.
Originally Posted by tempest
it should also be noted that even when everything's warmed up, the system can tempoararily go back into open loop during sudden transients, such as going into fuel enrichment when slamming on the hammer.
I do agree that the ECM gets no temperature information from the O2, in ANY C4, except when it begins receiving usable O2 voltages.
RACE ON!!!
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Originally Posted by CFI-EFI
I disagree. I've been perusing my manual and I find no mention of "timers". I don't deny their existence, but I don't see them mentioned.
maybe one experiment you can do to confirm this is to have your scanner hooked up and watch the open/closed loop flag and time it with a stopwatch. doing this with a cold engine may not be easy since coolant temp is also a major factor in closed loop enable - the closed loop timers may reach their enable threshold before the coolant temp threshold is met. a warm engine, however, may produce more consistent times between starting the engine and the system indicates it's in closed loop.
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Originally Posted by CFI-EFI
One reason I don't buy the "but it is done mainly by "waiting" via timers for the sensor to warm up" theory, is that the timers would require a warm engine to "wait" for the timers as long if it were cold, and delay closed loop when the engine is otherwise ready. I don't think the EPA would sign off on THAT one.
in an ideal world, i agree with you that an 02 temp sensor would be a great way to detect a "hot and ready" sensor, but to save costs, i would have a hard time finding a car (even with today's emissions standards) with such a sensor.
if i'm not mistaken, there are ECM algorithms now that can recognize a "hot" O2 sensor based on the signal pattern. i don't remember if such algorithms require wideband O2's....
Last edited by tempest; Feb 25, 2005 at 07:21 PM.
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Originally Posted by CFI-EFI
"The sensor is like an open circuit and produces no voltage when it is below about 360*C (600*F). An open sensor circuit or cold sensor causes open loop operation"
and sorry... i take back my statement that it is mainly the timers which determine the O2 sensor is hot. it a combination of the sensor voltage reading and timers both.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by tempest
i can only say "trust me on this one".
Originally Posted by tempest
in an ideal world, i agree with you that an 02 temp sensor would be a great way to detect a "hot and ready" sensor,
Originally Posted by tempest
if i'm not mistaken, there are ECM algorithms now that can recognize a "hot" O2 sensor based on the signal pattern.
Originally Posted by 1984 Corvette Service Manual
The sensor is like an open circuit and produces no voltage when it is below about 360*C (600*F). An open sensor circuit or cold sensor causes open loop operation.
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Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Originally Posted by CFI-EFI
There is no need for an O2 temp sensor. When the temp is sufficient, It WORKS.
Originally Posted by CFI-EFI
If it's "timers" Why does it go closed loop, immediately, with a very short cool down? I say it's because the O2 is still hot. If it were timers, the wait would be the same.
CFI, just curious, after a hot restart do you see it go immediately into closed loop or after something like 5-10 seconds?
again, sorry for the mis-information.
Last edited by tempest; Feb 25, 2005 at 08:51 PM.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Originally Posted by CFI-EFI
The O2 must reach a temperature of approx 600*F in order to send usable info to the ECM. If the O2 has been relocated or warms up too slowly the "12v feed" powers a heater to help get the O2 up to and maintain operating temp.
RACE ON!!!
RACE ON!!!
Here is a "borrowed" excerpt of O2 voltage output for "Rich" and "Lean" conditions during CL operation....Here's a pic of CL operation. Like CFI-EFI said, It's a circle: O2 > ECM > injectors > O2. (what I like to call feedaback):
Above 600F degrees, the narrow band oxygen sensor generates an output voltage proportional to the oxygen content of the exhaust gas. This oxygen sensor compares the oxygen present in the exhaust gas to the outside atmosphere oxygen content. When the exhaust gas mixture becomes rich, there is less oxygen left because the fuel burn used up most of the oxygen. When the mixture is lean, then there is not enough fuel to use up all the oxygen, which results in unburned surplus oxygen. These rich and lean conditions cause the narrow band OS to sharply switch between 0.6VDC (600mv when rich) and 0.3VDC (300mv when lean). The reference point for this switching action is referred to as the stoichiometric point (a/f/r = 14.7:1).
Last edited by MikeC4; Feb 25, 2005 at 08:41 PM.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by tempest
i agree. i did not realize that early on in the thread.
as i mentioned above, i've retracted my argument that the timers are the main condition to tell the sensor is ready. i was wrong there. in the applications that i have dealt with, however, there is a short time after starting the engine (a few seconds) where the system will wait to go into closed loop. it is that short timer i was mistaking as an "O2 ready" timer.
CFI, just curious, after a hot restart do you see it go immediately into closed loop or after something like 5-10 seconds?
again, sorry for the mis-information.
as i mentioned above, i've retracted my argument that the timers are the main condition to tell the sensor is ready. i was wrong there. in the applications that i have dealt with, however, there is a short time after starting the engine (a few seconds) where the system will wait to go into closed loop. it is that short timer i was mistaking as an "O2 ready" timer.
CFI, just curious, after a hot restart do you see it go immediately into closed loop or after something like 5-10 seconds?
again, sorry for the mis-information.
To be honest, I haven't observed that closely to know if it's immediate or 5 - 10 seconds. I'd bet on the short delay, though. I never meant to dispute the existence of "timers". They weren't mentioned in my book and it was my feeling that you were giving them credit for playing a bigger role than we both seem to know at this point.
RACE ON!!!