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Old 10-22-2002, 04:59 PM   #1
GregUnd
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Default How come our O2 sensor does NOT adjust A/F ratio?

I was reading and suposebly the O2 sensor's job is to tell the computer how much oxygen is in the exaust and allow it to adjust the A/F ratio....... I was always told that our ECU's do not do this? I knew that the O2 sensor was there to read how much oxygen was in the exaust but I did NOT know that the ECU was supposed to adjust the a/f ratio.... Mebe our ECU's DO adjust the a/f ratio and mebe this is why the cut out raises EGT's????? Help, i'm kinda nervouse now....
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Old 10-22-2002, 05:28 PM   #2
GregUnd
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Coming out of HowStuffWorks.com


"When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to. "
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Old 10-22-2002, 05:50 PM   #3
Sam2
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You have to know about open -loop and closed-loop and when you're in which. before you know the answesr to what you ask.
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Old 10-22-2002, 05:53 PM   #4
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Quote:
Originally posted by Sam2
You have to know about open -loop and closed-loop and when you're in which. before you know the answesr to what you ask.
Please explain....
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Old 10-22-2002, 06:14 PM   #5
Sam2
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There's too much to cover for a post-it note. Study, my friend, study. Probably about a dozen sensors all figure into how much fuel to squirt in the next squirt.

http://www.ecutek.com.au/oem_data.htm
http://www.eiccd.cc.ia.us/~dhanan/ep2/NOTES7.TRP.html
http://members.shaw.ca/costall/ECUprimer/index.html
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Old 10-22-2002, 06:15 PM   #6
Legacy777
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I might get this backwards.....so if I do....someone say so....

Closed loop is when your ecu is taking readings from the O2 sensor and making fine adjustments to the mix to get it as close to stiochiometric as possible. This usually takes place when you're cruising down the highway.

Open loop is when the ecu is pretty much just dumping fuel into the engine based on MAF/MAP, TPS, and other sensors readings. Usually when this is taking place, you will run rich.

This happens when the car is cold.....also when you dump it....and around town, especially if you are on and off the gas. I doubt the ecu really would benefit from going into closed loop mode around town.....too much erradic throttle adjustments and such.

So....driving around in Houston.....you're rarely going to get into a steady closed loop mode for any length of time.

I'm pretty sure that's right. anyone agree/disagree with what I said.

josh
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Old 10-22-2002, 11:40 PM   #7
JohnGalt00
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I'm far from an expert on this as well, but AFAIK, you're on closed loop all the time below 60% TPS, or below some RPM like 4000.
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Old 10-23-2002, 08:51 AM   #8
jmott
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Default Re: How come our O2 sensor does NOT adjust A/F ratio?

Quote:
Originally posted by GregUnd
I was reading and suposebly the O2 sensor's job is to tell the computer how much oxygen is in the exaust and allow it to adjust the A/F ratio....... I was always told that our ECU's do not do this? I knew that the O2 sensor was there to read how much oxygen was in the exaust but I did NOT know that the ECU was supposed to adjust the a/f ratio.... Mebe our ECU's DO adjust the a/f ratio and mebe this is why the cut out raises EGT's????? Help, i'm kinda nervouse now....
the ECU can adjust the air fuel ratio, but it only does this work at idle and part throttle, because the 02 sensor cant react fast enough for operation at WOT. this is true of pretty much all cars.

at idle, if the car sees the engine running a bit rich, it will prescribe a correction factor (say, -5) to lean the car out and get it to the proper air/fuel ratio.

then, at WOT, it will apply that same correction factor to the static WOT fuel maps.

this works pretty well, but its correction abilities are limited. For instance, STI injectors put it out of range for this system to work at WOT.
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Old 10-23-2002, 08:53 AM   #9
jmott
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your actually in closed loop most of the time. only when you get on it does it switch to open loop, for the reason I described above


Quote:
Originally posted by legacy777
I might get this backwards.....so if I do....someone say so....

Closed loop is when your ecu is taking readings from the O2 sensor and making fine adjustments to the mix to get it as close to stiochiometric as possible. This usually takes place when you're cruising down the highway.

Open loop is when the ecu is pretty much just dumping fuel into the engine based on MAF/MAP, TPS, and other sensors readings. Usually when this is taking place, you will run rich.

This happens when the car is cold.....also when you dump it....and around town, especially if you are on and off the gas. I doubt the ecu really would benefit from going into closed loop mode around town.....too much erradic throttle adjustments and such.

So....driving around in Houston.....you're rarely going to get into a steady closed loop mode for any length of time.

I'm pretty sure that's right. anyone agree/disagree with what I said.

josh
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Old 10-23-2002, 10:50 AM   #10
D_REX
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Just wondering why we use WB O2 sensors to measure A/F ratios for WOT tuning. If they don't react fast enough for an ECU to make corrections based off of their readings, how can we expect them to ract fast enough to tell me I need more fuel at 5Krpm etc.?

I've been looking at getting one of these DIY WB O2 sensors to use when I'm tuning, and this thread just brought this question to light.

Later,
Dustin
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Old 10-23-2002, 10:53 AM   #11
jmott
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Quote:
Originally posted by D_REX
Just wondering why we use WB O2 sensors to measure A/F ratios for WOT tuning. If they don't react fast enough for an ECU to make corrections based off of their readings, how can we expect them to ract fast enough to tell me I need more fuel at 5Krpm etc.?

I've been looking at getting one of these DIY WB O2 sensors to use when I'm tuning, and this thread just brought this question to light.

Later,
Dustin
The problem of a human looking at a run over the rpm range, making adjustments, then trying again, is different than a car making adjustments in real time as a driver does whatever it is a driver does.

it seems like it might be possible to try and duplicate the mind of the tuner in an ECU that could tune the car after a few WOT passes or something. But then should that ECU do stuff like turn the car off if it sees you are running way to lean at the moment like a dyno tuner would? etc...
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Old 10-23-2002, 10:59 AM   #12
D_REX
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Quote:
Originally posted by jmott


The problem of a human looking at a run over the rpm range, making adjustments, then trying again, is different than a car making adjustments in real time as a driver does whatever it is a driver does.

it seems like it might be possible to try and duplicate the mind of the tuner in an ECU that could tune the car after a few WOT passes or something. But then should that ECU do stuff like turn the car off if it sees you are running way to lean at the moment like a dyno tuner would? etc...
I'm refferring more specifically to the use of data logging (The tech edge stuff has data logging now) to dtermine your A/F ratio at an RPM and make adjustments based on that value. This would be the simplest possible implementation of closed loop control. Now I can see much more complicated algorithms using trends to determine needed adjustments, similar to your long term fuel trim but on a much more micro level.

If we cannot reliably use a WB O2 sensor to determine our A/F ratio at a given point then I want to identify that, and ideally quantify the error (be it a time shift or value shift), so that I can work around it.
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