Open Loop & Closed Loop - What is all this about?
01-17-2004, 04:50 PM
#1
Open Loop & Closed Loop - What is all this about?
I just made a couple of posts in the Australian forum where I mentioned "Closed Loop" and "Open Loop". I thought it might be a worthwhile thread if I started an explanation of what this all means, and how it works in conjuntion with piggy-back ECU's.
I repost this info here for those that don't frequent the Aussy forum... Happy reading!
Closed Loop
This condition is normally encountered at part throttle openings, such as encountered in "normal" driving. A simple explanation of what is happening here is that the PCM (Powertrain Control Module) is continously monitoring the O2 sensors in the exhaust. This device tells the PCM if the engine is running Rich or Lean. The RX-8 also has what is called a wideband O2 sensor, and this is used to tell how rich or lean the engine is running - hence the PCM gets a very accurate reading.
Locked away inside the PCM is some reference tables where, for a particlar load/RPM/thottle condition, the target AFR is found. The PCM continously monitors the AFR and adjusts the fuel delivery constantly to try to obtain that AFR. Constant feedback/adjustment, hence the term "closed loop"
There are a few other things that come into play here, known as STFT and LTFT - and this is all related to "learning". I'll leave a discussion about that untill another time.
Open Loop
This condition is normally reserved for WOT. The feedback loop from the O2 sensor is no longer operational. Hence the term Open Loop. In this case, the computer determines the amount of fuel delivery (and spark timing) from some calibration tables that are again locked away inside the PCM.
One of the main sensors the PCM uses to determine the fuel requirements is the MAF (Mass Air Flow). The way piggy back ECU work is that they alter the signal the PCM is getting from the MAF in such a way that the PCM grabs a fuel "doseage" value from a diferent part of the fuel table. If you alter the MAF signal up or down by the right amount, you can pinpoint more or less fuel - hence adjust the mixture richer or leaner. Depending on the fuel maps in the PCM, this altered MAF signal probably needs different adjustmets at all RPM points.
So where does this leave us?
What is all means is that a piggy back fuel controller shouldn't make any difference to normal, part throttle (Closed Loop) driving. It should not make any difference to economy either, or to emmissions.
Why is that? Because in Closed Loop, the computer is continually adjusting the fuel delivery to obtain a target AFR. The target AFR is locked away in the PCM. To my knowlede the fuel controllers don't fool the PCM with a butchered O2 reading. Over time, the different amounts of fuel required at different load points will be learned by the PCM (this is where those STFT and LTFT come in), and negate the changes to the MAF signal.
That is also one reason not to play with the MAF too much - in closed loop there will be no differences, and if you fiddle with screens etc you will bugger up the accuracy - they rely on a nice laminar flow of air.
But with a fuel controller that has been calibrated properly to fool the computer to think a different amount of air is incoming at WOT, then since the computer is in closed loop, you can alter the performance of the engine. A "Piggy Back ECU" is really fooling the computer. Done properly by an experienced tuner, one can achieve measured gains - if the state of tune is conservative in the first place.
The other answer is to get inside the computer and find all the look-up tables, understand their structure, and change them. That is a lot harder to do.
I hope this has been an interesting lesson in de-mystifying the working of your cars "computer" to some extent. I love understanding what is going on inside there.
Cheers,
Hymee.
I repost this info here for those that don't frequent the Aussy forum... Happy reading!
Closed Loop
This condition is normally encountered at part throttle openings, such as encountered in "normal" driving. A simple explanation of what is happening here is that the PCM (Powertrain Control Module) is continously monitoring the O2 sensors in the exhaust. This device tells the PCM if the engine is running Rich or Lean. The RX-8 also has what is called a wideband O2 sensor, and this is used to tell how rich or lean the engine is running - hence the PCM gets a very accurate reading.
Locked away inside the PCM is some reference tables where, for a particlar load/RPM/thottle condition, the target AFR is found. The PCM continously monitors the AFR and adjusts the fuel delivery constantly to try to obtain that AFR. Constant feedback/adjustment, hence the term "closed loop"
There are a few other things that come into play here, known as STFT and LTFT - and this is all related to "learning". I'll leave a discussion about that untill another time.
Open Loop
This condition is normally reserved for WOT. The feedback loop from the O2 sensor is no longer operational. Hence the term Open Loop. In this case, the computer determines the amount of fuel delivery (and spark timing) from some calibration tables that are again locked away inside the PCM.
One of the main sensors the PCM uses to determine the fuel requirements is the MAF (Mass Air Flow). The way piggy back ECU work is that they alter the signal the PCM is getting from the MAF in such a way that the PCM grabs a fuel "doseage" value from a diferent part of the fuel table. If you alter the MAF signal up or down by the right amount, you can pinpoint more or less fuel - hence adjust the mixture richer or leaner. Depending on the fuel maps in the PCM, this altered MAF signal probably needs different adjustmets at all RPM points.
So where does this leave us?
What is all means is that a piggy back fuel controller shouldn't make any difference to normal, part throttle (Closed Loop) driving. It should not make any difference to economy either, or to emmissions.
Why is that? Because in Closed Loop, the computer is continually adjusting the fuel delivery to obtain a target AFR. The target AFR is locked away in the PCM. To my knowlede the fuel controllers don't fool the PCM with a butchered O2 reading. Over time, the different amounts of fuel required at different load points will be learned by the PCM (this is where those STFT and LTFT come in), and negate the changes to the MAF signal.
That is also one reason not to play with the MAF too much - in closed loop there will be no differences, and if you fiddle with screens etc you will bugger up the accuracy - they rely on a nice laminar flow of air.
But with a fuel controller that has been calibrated properly to fool the computer to think a different amount of air is incoming at WOT, then since the computer is in closed loop, you can alter the performance of the engine. A "Piggy Back ECU" is really fooling the computer. Done properly by an experienced tuner, one can achieve measured gains - if the state of tune is conservative in the first place.
The other answer is to get inside the computer and find all the look-up tables, understand their structure, and change them. That is a lot harder to do.
I hope this has been an interesting lesson in de-mystifying the working of your cars "computer" to some extent. I love understanding what is going on inside there.
Cheers,
Hymee.
01-17-2004, 05:47 PM
#2
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HYMEE
I am truly fortunate to have availability to your LOOPY knowledge for the testing of maurices stage 1 kit for the Australian RX8 S .
Go fed ex go 2 days to count down .
cheers
michael
I am truly fortunate to have availability to your LOOPY knowledge for the testing of maurices stage 1 kit for the Australian RX8 S .
Go fed ex go 2 days to count down .
cheers
michael
01-23-2004, 01:02 AM
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probably, Hymee, because very few of us fully understand it.
I, for example, am a pre-IT baby boomer. If it is more complex than tuning a SU carbie, then I'm too old.
jack.
I, for example, am a pre-IT baby boomer. If it is more complex than tuning a SU carbie, then I'm too old.
jack.
01-23-2004, 04:34 AM
#6
Yes, I believe that is the case. I have witnessed that via my OBDII scan tool.
I would say the reason is at startup, there is a fuel/spark table that is looked up against intake temperature as one of the main variables. The O2 sensors don't work untill they get to a certain temperature either, so that would also rule out closed loop at cold start.
Cheers,
Hymee.
I would say the reason is at startup, there is a fuel/spark table that is looked up against intake temperature as one of the main variables. The O2 sensors don't work untill they get to a certain temperature either, so that would also rule out closed loop at cold start.
Cheers,
Hymee.
01-23-2004, 10:42 AM
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This all comes into play greatly with turbo charged vehicles, i believe the code is po103 or something like that, if you trigger this cel and use a pocketlogger (this is a great tool to have for obdII cars. using an apexi s-afc can help tune for this you will neeed to tune your high and low throttle settings, but most importantly to rid yourself of this code using the s-afc you will need to change the %'s for high and low throttle something like 30% low 70% high. stft short term fuel trim ltft long term fuel trim, these are used when tuning a car under low throttle and high throttle you want to keep them as close to 0 as possible. This means your 02's are getting proper readings and the fuel mixture is correct in each rpm level. one thing to look at to help you tune your car is youe 02 volts a good range for tune is between 85v and 94v.
01-23-2004, 11:55 AM
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The target AFR is locked away in the PCM. To my knowlede the fuel controllers don't fool the PCM with a butchered O2 reading.
One thing I would ask would be, are the reference tables completely locked away? Is it known that you a) cannot change the values, say, target AFR, and b) cannot redirect the PCM to look at a separate device such as the piggy-back that has its own programmable reference tables/target AFRs?
I need to go back and read some of canzoomer's and syntrix's threads during testing to match it up in my brain that they were in fact just tuning open loop/@ WOT. I have it in my brain for some reason that 1) things run pig rich even at partial throttle/idle, more or less in some ranges of the powerband but still pretty rich overall, and 2) that piggy-back units or programmable fuel mapping devices like the greddy were addressing that, and not just open loop/WOT.
Maybe you guys can help me out in the meantime until I can go search and read up.
01-23-2004, 02:39 PM
#10
Originally posted by jeffscardinal
This all comes into play greatly with turbo charged vehicles, i believe the code is po103 or something like that, if you trigger this cel and use a pocketlogger (this is a great tool to have for obdII cars. using an apexi s-afc can help tune for this you will neeed to tune your high and low throttle settings, but most importantly to rid yourself of this code using the s-afc you will need to change the %'s for high and low throttle something like 30% low 70% high. stft short term fuel trim ltft long term fuel trim, these are used when tuning a car under low throttle and high throttle you want to keep them as close to 0 as possible. This means your 02's are getting proper readings and the fuel mixture is correct in each rpm level. one thing to look at to help you tune your car is youe 02 volts a good range for tune is between 85v and 94v.
This all comes into play greatly with turbo charged vehicles, i believe the code is po103 or something like that, if you trigger this cel and use a pocketlogger (this is a great tool to have for obdII cars. using an apexi s-afc can help tune for this you will neeed to tune your high and low throttle settings, but most importantly to rid yourself of this code using the s-afc you will need to change the %'s for high and low throttle something like 30% low 70% high. stft short term fuel trim ltft long term fuel trim, these are used when tuning a car under low throttle and high throttle you want to keep them as close to 0 as possible. This means your 02's are getting proper readings and the fuel mixture is correct in each rpm level. one thing to look at to help you tune your car is youe 02 volts a good range for tune is between 85v and 94v.
The RX-8 has a wideband O2 sensor. Wideband O2's use current, not voltage to report the lambda. "Normal" voltage based O2 sensors are not linear, and are really only good to indicate rich or lean or stoich. But not the degree of richness or lean-ness. It would be advisable to tune with the wideband, not the normal one (which the RX-8 has as well).
If you reset the fuel trims, the PCM will re-learn them after a while anyway. That is what closed loop is all about.
Cheers,
Hymee.
Last edited by Hymee; 01-23-2004 at 02:41 PM.
01-23-2004, 03:05 PM
#12
Two observations:
First, the RX-8 does not appear to delineate between "open" and "closed" loop.
Since the front O2 sensor is used to set lambda values for the PCM under wide open throttle, there isn't a real "open" loop anywhere in the programming.
Second, the PCM in the RX-8 seems to assume a certain response curve for the MAF and trusts it will remain that way.
That means that adjustments to the "closed" loop parts of the map DO have the same effect as those to the "open" part.
When I do tuning runs for the E-Manage, I do 5 seperate logs:
One each for 20%, 50%, 70% and 100% throttle and one for a standing 1/4 mile.
I then tune each of those ranges seperately. The PCM does respond in kind and does not attempt to "un-learn" what I have dialed in.
I actually found that I could make a significant change for the better in the drivability at part throttle.
At 70%, the lumps and sags in the power curve that happen at 4200 and 6200 RPM are more pronounced in the OEM tuning. I dialed those almost completely out with the E-Manage.
First, the RX-8 does not appear to delineate between "open" and "closed" loop.
Since the front O2 sensor is used to set lambda values for the PCM under wide open throttle, there isn't a real "open" loop anywhere in the programming.
Second, the PCM in the RX-8 seems to assume a certain response curve for the MAF and trusts it will remain that way.
That means that adjustments to the "closed" loop parts of the map DO have the same effect as those to the "open" part.
When I do tuning runs for the E-Manage, I do 5 seperate logs:
One each for 20%, 50%, 70% and 100% throttle and one for a standing 1/4 mile.
I then tune each of those ranges seperately. The PCM does respond in kind and does not attempt to "un-learn" what I have dialed in.
I actually found that I could make a significant change for the better in the drivability at part throttle.
At 70%, the lumps and sags in the power curve that happen at 4200 and 6200 RPM are more pronounced in the OEM tuning. I dialed those almost completely out with the E-Manage.
01-23-2004, 03:49 PM
#13
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hmm.. I don't frequent these discussions much so please excuse me if my post is not 100% relevant to the programming of the ECU and other computer functions.
So after reading a couple of the posts.. Hymee you have a pretty good example but it may be a little to complicated for those who don't know about some of the functions of the ECU (I will admit I only have a rough grasp)
But , I really haven't seen a good definition of Open loop and closed loop. systems.
So open loop:
getting away form a complicated thing as your ECU we can liken this to a simple washing machine. You turn it on and it goes through its cycle. How do you control the cleanliness of your cloths? well you can't unless you modify some of the inputs (soap wash-time etc). This is similar to some of the ECU function. It takes an input and then produces a set output. Nothing complicated here
Closed loop:
This is where things get fun! A simple example would be your toilet. You flush but instead of just filling the tank for a certain amount of time (like you washing machine) your toilet has a sensor (the floating thingy)! This produces a "signal" (just a lever) back to the valve which will start to proportionally close the valve until the toilet tank has reached the proper water height.
This simple example can then be extrapolated to a much much more complicated functions of the ECU.
Now I am sure you can probably see a lot of closed loop systems now.. ie cruise control.. etc
A little bit more technical as I don't have much experience with (but would like to learn): the electronics. So Hymee you are saying that the piggy back system is directly connected right before the PCM. So essentially the piggybacked-unit is just spoofing a different value to the PCM?
This seems like a really hack job(sorry if this sounds rude) as I am not used to seeing things done like that. Ideally you would want to really put in a new look up table in the original ECU but I guess that is kinda out of the question right?
Also the piggy backing can be tough because one of the interesting things about closed loop control systems is that they can go unstable! So that Piggybacked ECU has really got to be tested well for the values it outputs(and the time lag it induces) hehe.
Interesting stuff!
if you guys have anything I could read more about this I would love to get my hands on it! I would really like to be able to see a flow diagram to really understand how all the systems work together!
So after reading a couple of the posts.. Hymee you have a pretty good example but it may be a little to complicated for those who don't know about some of the functions of the ECU (I will admit I only have a rough grasp)
But , I really haven't seen a good definition of Open loop and closed loop. systems.
So open loop:
getting away form a complicated thing as your ECU we can liken this to a simple washing machine. You turn it on and it goes through its cycle. How do you control the cleanliness of your cloths? well you can't unless you modify some of the inputs (soap wash-time etc). This is similar to some of the ECU function. It takes an input and then produces a set output. Nothing complicated here
Closed loop:
This is where things get fun! A simple example would be your toilet. You flush but instead of just filling the tank for a certain amount of time (like you washing machine) your toilet has a sensor (the floating thingy)! This produces a "signal" (just a lever) back to the valve which will start to proportionally close the valve until the toilet tank has reached the proper water height.
This simple example can then be extrapolated to a much much more complicated functions of the ECU.
Now I am sure you can probably see a lot of closed loop systems now.. ie cruise control.. etc
A little bit more technical as I don't have much experience with (but would like to learn): the electronics. So Hymee you are saying that the piggy back system is directly connected right before the PCM. So essentially the piggybacked-unit is just spoofing a different value to the PCM?
This seems like a really hack job(sorry if this sounds rude) as I am not used to seeing things done like that. Ideally you would want to really put in a new look up table in the original ECU but I guess that is kinda out of the question right?
Also the piggy backing can be tough because one of the interesting things about closed loop control systems is that they can go unstable! So that Piggybacked ECU has really got to be tested well for the values it outputs(and the time lag it induces) hehe.
Interesting stuff!
if you guys have anything I could read more about this I would love to get my hands on it! I would really like to be able to see a flow diagram to really understand how all the systems work together!
01-24-2004, 01:43 AM
#14
A closed loop system will only become unstable if the feedback time exceeds the response time of the original system.
That wont happen here.
Think of a piggy-back air/fuel controller as a pair of sunglasses and you have a better analogy.
Your irises will react at a rate determined by the amount of light hitting your retina.
Now, put on a pair of sunglasses.
Your retina simply gets less light, so your irises don't react as much.
That wont happen here.
Think of a piggy-back air/fuel controller as a pair of sunglasses and you have a better analogy.
Your irises will react at a rate determined by the amount of light hitting your retina.
Now, put on a pair of sunglasses.
Your retina simply gets less light, so your irises don't react as much.
01-24-2004, 04:05 AM
#15
Originally posted by Maniac
Two observations:
First, the RX-8 does not appear to delineate between "open" and "closed" loop.
Since the front O2 sensor is used to set lambda values for the PCM under wide open throttle, there isn't a real "open" loop anywhere in the programming.
Second, the PCM in the RX-8 seems to assume a certain response curve for the MAF and trusts it will remain that way.
That means that adjustments to the "closed" loop parts of the map DO have the same effect as those to the "open" part.
When I do tuning runs for the E-Manage, I do 5 seperate logs:
One each for 20%, 50%, 70% and 100% throttle and one for a standing 1/4 mile.
I then tune each of those ranges seperately. The PCM does respond in kind and does not attempt to "un-learn" what I have dialed in.
I actually found that I could make a significant change for the better in the drivability at part throttle.
At 70%, the lumps and sags in the power curve that happen at 4200 and 6200 RPM are more pronounced in the OEM tuning. I dialed those almost completely out with the E-Manage.
Two observations:
First, the RX-8 does not appear to delineate between "open" and "closed" loop.
Since the front O2 sensor is used to set lambda values for the PCM under wide open throttle, there isn't a real "open" loop anywhere in the programming.
Second, the PCM in the RX-8 seems to assume a certain response curve for the MAF and trusts it will remain that way.
That means that adjustments to the "closed" loop parts of the map DO have the same effect as those to the "open" part.
When I do tuning runs for the E-Manage, I do 5 seperate logs:
One each for 20%, 50%, 70% and 100% throttle and one for a standing 1/4 mile.
I then tune each of those ranges seperately. The PCM does respond in kind and does not attempt to "un-learn" what I have dialed in.
I actually found that I could make a significant change for the better in the drivability at part throttle.
At 70%, the lumps and sags in the power curve that happen at 4200 and 6200 RPM are more pronounced in the OEM tuning. I dialed those almost completely out with the E-Manage.
Firstly I want to make it clear from the outset that I am not trying to discredit your results. I am quite impressed with what you have done, and give you lots of kudos for being a pioneer with the eManage on the RX-8. I have seriously considered going down that path.
With all due respect though, the ECU does have Open Loop and Closed loop modes. I know because the computer tells me so.
I would like to know the "longevity" of the closed loop gains you see. In theory (and I admit none of us know the exact inner workings of the PCM yet), over time the LTFTs and the STFTs should adjust to achieve the same AFR's as it has been "told" to obtain.
What I would like to do is go for a drive with some logging happening, and produce a graph of "Fuel System Status" (open or closed loop), Speed, RPM, TPS, Wideband O2, Commanded (target) O2 etc.
I am waiting for a hardware update that will allow me to log more paramters at once - hence more frequent updates. Then I need to do some work on extracting the raw values from the logs, and plot them on a graph of some sort.
I have been looking at some OCX's for doing that. If anyone has some info on OCX's that can be used for graphing, please let me know. So far I have been looking at "Dragonfly" and "Flipper Graph Control"
Cheers,
Hymee.
01-24-2004, 04:12 AM
#16
Originally posted by Kaliken
So Hymee you are saying that the piggy back system is directly connected right before the PCM. So essentially the piggybacked-unit is just spoofing a different value to the PCM?
This seems like a really hack job(sorry if this sounds rude) as I am not used to seeing things done like that. Ideally you would want to really put in a new look up table in the original ECU but I guess that is kinda out of the question right?
So Hymee you are saying that the piggy back system is directly connected right before the PCM. So essentially the piggybacked-unit is just spoofing a different value to the PCM?
This seems like a really hack job(sorry if this sounds rude) as I am not used to seeing things done like that. Ideally you would want to really put in a new look up table in the original ECU but I guess that is kinda out of the question right?
Yes - Essentially think of most Piggy Backs plugging in "before" the PCM - to alter incoming signals.
One exception I know of is Ric Shaws tunable unit. It does not alter the signals coming in, but takes control of the duty cycle of the fuel injectors as well as the ignition firing "on the way out". I am quite impressed with this concept. One advantage is has is that you are not messing with any thing else the computer might be controlling. As an example, think about this - Lets just pretend that the PCM controls the amount of oil being injected to protect the seals via a decision it makes upon the signal it is getting from the Mass Air Flow sensor? What happens to the doseage then if you spoof your MAF? You can see why vehicle manufacturers void powertrain warranties due to piggy back PCM's.
"Ideally..." - I believe you are correct. It is "kinda" out of the question, the ECU software is not something you can go get out of Open Source.
If someone can swing me a copy I would more than happy to step up to the plate
Cheers,
Hymee
Last edited by Hymee; 01-24-2004 at 04:20 AM.
01-24-2004, 11:37 AM
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Great point Hymee....about how the MAF signals being altered.
Without knowing the entire script from the OEM PCM, its hard to tell what else the computer may or may not base "piggyback warped values" to make other decisions. Interesting thought.
About the point brought up about how a Piggyback FC is hack as compared to new lookup tables and values placed on the PCM itself...I agree to a point.
I'm a purist however...and would rather a reprogrammed ECU over a unit to fool the ECU that I currently have. What Ric Shaw is going to sell is somewhat unknow to most at this point as far as the specifics....and how it interacts with the ECU compared to Canzoomers.
What is certain is that Racing Beat plans to modify the ECU with new software in the form of a software update. You send then your ECU...they fash it with the new software designed by them....done. What the power gains are...we dont know yet, but I like the idea of a refashed ECU rather than whats offered at this time. RB says they are very close to completion........it may be worth the wait.
Without knowing the entire script from the OEM PCM, its hard to tell what else the computer may or may not base "piggyback warped values" to make other decisions. Interesting thought.
About the point brought up about how a Piggyback FC is hack as compared to new lookup tables and values placed on the PCM itself...I agree to a point.
I'm a purist however...and would rather a reprogrammed ECU over a unit to fool the ECU that I currently have. What Ric Shaw is going to sell is somewhat unknow to most at this point as far as the specifics....and how it interacts with the ECU compared to Canzoomers.
What is certain is that Racing Beat plans to modify the ECU with new software in the form of a software update. You send then your ECU...they fash it with the new software designed by them....done. What the power gains are...we dont know yet, but I like the idea of a refashed ECU rather than whats offered at this time. RB says they are very close to completion........it may be worth the wait.
Last edited by Gyro; 01-24-2004 at 11:44 AM.
01-24-2004, 12:18 PM
#20
Are you logging through the DLC on OBD-II?
That is why you get the "open" and "closed" loop indications.
The car is required to indicate those points in the tuning to conform to OBD standards.
However, the computer continues to trim fuel based on the WBO2S, even at WOT where the car would, theoretically, be in "open" loop.
I have a separate WBO2S in front of the cat that is always installed, always on, and I log just about everywhere I drive.
I've been doing this for over a month.
My A/F ratios have stayed where I put them and I can adjust them at any throttle position.
If it of any use to you, I can send you a TON of Excel pages of data dumps from all kinds of driving scenarios.
That is why you get the "open" and "closed" loop indications.
The car is required to indicate those points in the tuning to conform to OBD standards.
However, the computer continues to trim fuel based on the WBO2S, even at WOT where the car would, theoretically, be in "open" loop.
I have a separate WBO2S in front of the cat that is always installed, always on, and I log just about everywhere I drive.
I've been doing this for over a month.
My A/F ratios have stayed where I put them and I can adjust them at any throttle position.
If it of any use to you, I can send you a TON of Excel pages of data dumps from all kinds of driving scenarios.
01-24-2004, 12:34 PM
#21
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thanks guys.. this is fun stuff. and all the props to canzoomer and maniac figuring all the stuff out to create a piggyback unit! I can fully understand the amount of work that went into it.
very cool!
And maniac your analogy is pretty good considering we are taking into consideration things that move at the speed of light. namely electrons in a circuit. So time delay would hardly be a factor here. But there are a lot of mechanical control systems that can go unstable because of time delay (or in the proper control terms: phase lag).
This is realy interesting stuff as it pertains to a lot of theings I studied in college. I will have to keep posted on this topic!
very cool!
And maniac your analogy is pretty good considering we are taking into consideration things that move at the speed of light. namely electrons in a circuit. So time delay would hardly be a factor here. But there are a lot of mechanical control systems that can go unstable because of time delay (or in the proper control terms: phase lag).
This is realy interesting stuff as it pertains to a lot of theings I studied in college. I will have to keep posted on this topic!
01-24-2004, 01:44 PM
#22
Originally posted by Maniac
Are you logging through the DLC on OBD-II?
That is why you get the "open" and "closed" loop indications.
The car is required to indicate those points in the tuning to conform to OBD standards.
However, the computer continues to trim fuel based on the WBO2S, even at WOT where the car would, theoretically, be in "open" loop.
I have a separate WBO2S in front of the cat that is always installed, always on, and I log just about everywhere I drive.
I've been doing this for over a month.
My A/F ratios have stayed where I put them and I can adjust them at any throttle position.
If it of any use to you, I can send you a TON of Excel pages of data dumps from all kinds of driving scenarios.
Are you logging through the DLC on OBD-II?
That is why you get the "open" and "closed" loop indications.
The car is required to indicate those points in the tuning to conform to OBD standards.
However, the computer continues to trim fuel based on the WBO2S, even at WOT where the car would, theoretically, be in "open" loop.
I have a separate WBO2S in front of the cat that is always installed, always on, and I log just about everywhere I drive.
I've been doing this for over a month.
My A/F ratios have stayed where I put them and I can adjust them at any throttle position.
If it of any use to you, I can send you a TON of Excel pages of data dumps from all kinds of driving scenarios.
If you would be happy to send them to me, I would be more than happy to have a look over them. As long as you realise I am no trying to have an argument with you, just trying to share experiences. I know you have put a lot of time, effort, and money into this.
It is indeed interesting that the AFR's are staying where you put them. It is like the computer is not even adjusting anything as it would in closed loop. That is incredible.
I hope the computer is not lying through it's OBDII DLC (yes, that is what I am reading). If it was it would surely be in breach of the whole CARB Emissions thing that is basically enshrined in law.
And if it was lying through that, what hope would the dealer have via the WDS system? It communicates with the vehicle via the same connector.
Just a quick question - You said "The car continues to trim fuel" and you also said your "AFRs stay where you put them". To me that is a bit of a contradiction. If the car continues to trim fuel, that is because it is trying to get target AFR's, however your AFR's are maintained. From what I understand, you are not altering the target AFR's per se, but essentially the amount of air flow detected. Do you see what I am getting at. Anyway - my theory is not worth much compared to your practical results!
Keep up the good work!
Cheers,
Hymee.
02-04-2004, 03:49 PM
#25
OK, I think I now know a little bit more that helps me understand the experiences Jeff has posted.
In Closed loop, the "target AFRs" are locked away in the PCM, and the PCM looks for a target AFR based on RPM and MAF (and maybe something else). So the trick in tuning is then to alter the MAF signal just the right amount so the computer goes looking in another part of the table and gets a target AFR that is the one you are looking for. The computer then adjusts the fuel delivery until that AFR is obtained via the wideband O2 (Lambda) sensor.
This is where the fuel trims come into play: the computer records the adjustment it last made for that condition, and it is looked up first - sort of like a level 1 cache - and hopefully gets the AFR right the first go. If it doesn't get the AFR right the first go, it "Trims" it (via the closed feedback loop), and stores that adjustment in the Fuel Trims, to be used next time that condition is reached.
All of this is happening many, many times per second. It is really a marvel of engineering what that little computer is doing! Most people simply put the key in, start it and drive it.
Cheers,
Hymee.
PS - Thanks to Canzoomer for explaining to me how the MAF signal can be used to our advantage in Closed Loop!
In Closed loop, the "target AFRs" are locked away in the PCM, and the PCM looks for a target AFR based on RPM and MAF (and maybe something else). So the trick in tuning is then to alter the MAF signal just the right amount so the computer goes looking in another part of the table and gets a target AFR that is the one you are looking for. The computer then adjusts the fuel delivery until that AFR is obtained via the wideband O2 (Lambda) sensor.
This is where the fuel trims come into play: the computer records the adjustment it last made for that condition, and it is looked up first - sort of like a level 1 cache - and hopefully gets the AFR right the first go. If it doesn't get the AFR right the first go, it "Trims" it (via the closed feedback loop), and stores that adjustment in the Fuel Trims, to be used next time that condition is reached.
All of this is happening many, many times per second. It is really a marvel of engineering what that little computer is doing! Most people simply put the key in, start it and drive it.
Cheers,
Hymee.
PS - Thanks to Canzoomer for explaining to me how the MAF signal can be used to our advantage in Closed Loop!