O2 sensors needed for closed loop?

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I always thought oxygen sensors were needed for closed loop operation. My beater 2000 Corolla has neither the front or rear sensor connected but I can still 'trick' it into entering closed loop. I let the engine get to about 185 F or higher, turn the car off for a few seconds, then restart it and after a few more seconds my Ultragauge shows it's now in closed loop mode.
 
Interesting. It must assume the zero volts to be a real lean reading and then compensate until it senses trouble. How quickly does it throw a code?

Fun fact, "Closed loop" can mean more than cars, it can be a business structure where every employee is empowered upon those above/below them, the process, etc.

An open loop employer would give an order then cease to monitor if it was getting done.
wink.gif
 
When you perform this trick, what is the difference in fuel consumed? Why are your O2 sensors not in-service?
 
Interesting , usually you need atleast the front before cat sensors to get closed loop operation, how its doing that without one sounds like a glitch or im just misinformed.
 
Its called FMEM...Failure Mode Effect Management. When you lose a sensor input, the PCM "infers" the missing sensor reading. Lose an O2, PCM determines fuel pulse width by TP position and MAF reading. PCM looks up the combination from its own tables and runs what it thinks will be a "0" fuel trim.
 
Originally Posted By: gathermewool
When you perform this trick, what is the difference in fuel consumed? Why are your O2 sensors not in-service?


The front one is out of service because some time before I bought the car, someone disconnected part of the exhaust and cut the wires to the sensor and welded a piece of metal over the O2 bung. The rear sensor's wires were also cut but at least the sensor is actually still there. I haven't really noticed any major MPG improvement when in closed loop
 
Originally Posted By: 55Test
Originally Posted By: gathermewool
When you perform this trick, what is the difference in fuel consumed? Why are your O2 sensors not in-service?


The front one is out of service because some time before I bought the car, someone disconnected part of the exhaust and cut the wires to the sensor and welded a piece of metal over the O2 bung. The rear sensor's wires were also cut but at least the sensor is actually still there. I haven't really noticed any major MPG improvement when in closed loop


Well, it's not closed loop, regardless of what it says--no O2, no feedback, ergo no loop to be closed.
 
Originally Posted By: supton
Originally Posted By: 55Test
Originally Posted By: gathermewool
When you perform this trick, what is the difference in fuel consumed? Why are your O2 sensors not in-service?


The front one is out of service because some time before I bought the car, someone disconnected part of the exhaust and cut the wires to the sensor and welded a piece of metal over the O2 bung. The rear sensor's wires were also cut but at least the sensor is actually still there. I haven't really noticed any major MPG improvement when in closed loop


Well, it's not closed loop, regardless of what it says--no O2, no feedback, ergo no loop to be closed.


That's kind of what I was getting at.

I can't see any reason why not having a front O2 is a good idea.
 
Sounds like the previous owner was a hack repair guy and I would be leary of other things he has done to the car to save a penny.
 
They are needed for "closed-loop" since the O2 provides feedback from the exhaust about how the mixture is affecting the emissions. I speculation I heard, however, is that your vehicle will enter open-loop if you accelerate particularly hard, like WOT.

Some mechanic disconnected the O2 on my vehicle. I drove around for 2.5 years not knowing (not fitted with a CEL), then discovered a disconnected harness zip-tied to the underbody... Was getting about 8.5L/100km highway, 10.5L/100km suburban.
After reconnecting, improved to about 7.5L/100k highway, 8.5-9.5L/100km suburban. Also noticed the exhaust didn't reek after a hill climb and a noticeable "shove" when going to WOT. Funnily enough, highway economy doesn't change much with or without A/C, or even when significantly laden.
 
Originally Posted By: SHOZ
Hyundai Accents in Iran have no O2s from the factory yet still go into closed loop.


Okay, my old Mazda also ran in closed-loop without O2 sensors. It all has to do with what the ECU is using to calculate values, if there is supposed to be a voltage input from an O2 sensor and there isn't one, then this is what the OP is asking about. If the engine control is built without the sensors then it isn't going to be looking for the input.
 
Originally Posted By: kschachn
Originally Posted By: SHOZ
Hyundai Accents in Iran have no O2s from the factory yet still go into closed loop.


Okay, my old Mazda also ran in closed-loop without O2 sensors. It all has to do with what the ECU is using to calculate values, if there is supposed to be a voltage input from an O2 sensor and there isn't one, then this is what the OP is asking about. If the engine control is built without the sensors then it isn't going to be looking for the input.
I would think though that the default programmed fuel trim tables would be similar though. It would seem they would use the best info whether any O2 input is there or not. With the O2s they make adjustments using the OEM data tables and the add or subtract and keep track of that in another data table that is writable.
 
In the OP's case it is really "broken loop", which can happen whether the system is open or closed loop. Not all processes require it to be closed loop (with feedback), some are just fine being open loop.

When a closed loop system loses a feedback parameter and has to substitute other data (whether from a lookup table or inferred from other available data), that's broken no matter how you look at it.
 
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