Open loop and closed loop????
Thread Starter
On The Tree
Joined: Nov 2001
Posts: 107
Likes: 0
From: Take a wild guess!!
Open loop and closed loop???? Can someone explain to me what open loop and closed loop mean?? AND where can you tune for this stuff..
AND.. Where in ATAP is the selection for timing between shifts.. ?? Thanks guys
<small>[ April 02, 2002, 03:41 PM: Message edited by: AJH LS1 Z28 ]</small>
AND.. Where in ATAP is the selection for timing between shifts.. ?? Thanks guys
<small>[ April 02, 2002, 03:41 PM: Message edited by: AJH LS1 Z28 ]</small>
Re: Open loop and closed loop???? There are five OBD-II fuel modes:
1. Open loop - Has not yet satisfied conditions to go closed loop
2. Closed loop - Using O2 sensors as feedback for fuel control
3. Open loop - Due to driving conditions
4. Open loop - Due to detected system fault
5. Closed loop - Fault with at least one O2 sensor - may be using single O2 sensor for fuel control.
The usual condition in mode 1 is that the O2 sensors are not hot enough - most O2 sensors these days are electrically heated and are ready within a few minutes of a cold start.
Mode 2 is the desired mode for you vehicle to be in.
MOde 3 is entered during power enrichment and deceleration fuel cutoff (manual cars). Although I have heard rumours (in this forum I think) that GM plan to build a PCM that stays in closed loop up to 100% throttle.
Mode 4 and 5 - fairly obvious and is usually acompanied by the illumination of the CEL.
Closed loop:
Petrol combustion engines are most clean burning when the air to fuel ratio (AFR) is 14.7.
Don't forget this fuel mode palava is all about emission control not about power. Most everyone on a race track will run richer than 14.7 - see the flames/black smoke from the exhaust <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> I digress.
The O2 sensors in the exhaust system detect the presence of oxygen in the exhaust gas. Too much oxygen and your car is running lean - too little oxygen and your car is running rich.
The signals from the O2 sensors are fed back into the PCM so that the PCM can make adjustments to the injector base pulse widths (IBPW) i.e. adjustments to how much fuel is squirted each time the injectors fire.
Because the O2 sensors "sense" the AFR "after the fact" the PCM can not use the current O2 signal for the current IBPW adjustment not in real-time anyway. Instead, the PCM "remembers" the last few O2 readings and calculates an estimated IBPW adjustment. This is called short term fuel trim and is designed to compensate for short term differences in engine operation - usually due to variations in the completeness of the fuel combustion.
The short term fuel trims are also averaged over a longer time period and "remebered" for certain RPM v's MAP or MAF values. These averages are called long term fuel trim - this is what is referred to as "learning". The PCM "learns" the best IBPW adjustments for certain RPM v's MAP or MAF values. These long term fuel trims are designed to allow your PCM to slowly alter it's IBPW to keep the AFR at 14.7 when long term conditions change - like engine wear, climate and fuel quality.
Tuning for closed loop mode is pretty much making adjustments to your base fuel tables (the base pulse widths are calculated from these fuel tables) so that your short and long term fuel trims approach zero. The closer you can get your fuel trims to zero the less the PCM is compensating.
Open loop:
Is quite simple - the feedback from the O2 sensors is NOT used - either because the O2 sensor values are invalid (mode 1 and 4) or the diving conditions require a non stoichiometric combustion - i.e. the PCM does not "care" about the AFR:
- Power enrichment = you've mashed your throttle to the floor.
- Decel fuel cutoff = you're coasting and the injectors have been closed, your engine is just a big air pump.
I guess tuning up the PE curve(s) would be about the only place I can think of for open loop operation.
I believe also that above about 70% throttle the PCM stops "learning" i.e. it doesn't update the long term fuel trims - not sure if it stops using the short term fuel trims though.
Regards
Paul
1. Open loop - Has not yet satisfied conditions to go closed loop
2. Closed loop - Using O2 sensors as feedback for fuel control
3. Open loop - Due to driving conditions
4. Open loop - Due to detected system fault
5. Closed loop - Fault with at least one O2 sensor - may be using single O2 sensor for fuel control.
The usual condition in mode 1 is that the O2 sensors are not hot enough - most O2 sensors these days are electrically heated and are ready within a few minutes of a cold start.
Mode 2 is the desired mode for you vehicle to be in.
MOde 3 is entered during power enrichment and deceleration fuel cutoff (manual cars). Although I have heard rumours (in this forum I think) that GM plan to build a PCM that stays in closed loop up to 100% throttle.
Mode 4 and 5 - fairly obvious and is usually acompanied by the illumination of the CEL.
Closed loop:
Petrol combustion engines are most clean burning when the air to fuel ratio (AFR) is 14.7.
Don't forget this fuel mode palava is all about emission control not about power. Most everyone on a race track will run richer than 14.7 - see the flames/black smoke from the exhaust <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> I digress.
The O2 sensors in the exhaust system detect the presence of oxygen in the exhaust gas. Too much oxygen and your car is running lean - too little oxygen and your car is running rich.
The signals from the O2 sensors are fed back into the PCM so that the PCM can make adjustments to the injector base pulse widths (IBPW) i.e. adjustments to how much fuel is squirted each time the injectors fire.
Because the O2 sensors "sense" the AFR "after the fact" the PCM can not use the current O2 signal for the current IBPW adjustment not in real-time anyway. Instead, the PCM "remembers" the last few O2 readings and calculates an estimated IBPW adjustment. This is called short term fuel trim and is designed to compensate for short term differences in engine operation - usually due to variations in the completeness of the fuel combustion.
The short term fuel trims are also averaged over a longer time period and "remebered" for certain RPM v's MAP or MAF values. These averages are called long term fuel trim - this is what is referred to as "learning". The PCM "learns" the best IBPW adjustments for certain RPM v's MAP or MAF values. These long term fuel trims are designed to allow your PCM to slowly alter it's IBPW to keep the AFR at 14.7 when long term conditions change - like engine wear, climate and fuel quality.
Tuning for closed loop mode is pretty much making adjustments to your base fuel tables (the base pulse widths are calculated from these fuel tables) so that your short and long term fuel trims approach zero. The closer you can get your fuel trims to zero the less the PCM is compensating.
Open loop:
Is quite simple - the feedback from the O2 sensors is NOT used - either because the O2 sensor values are invalid (mode 1 and 4) or the diving conditions require a non stoichiometric combustion - i.e. the PCM does not "care" about the AFR:
- Power enrichment = you've mashed your throttle to the floor.
- Decel fuel cutoff = you're coasting and the injectors have been closed, your engine is just a big air pump.
I guess tuning up the PE curve(s) would be about the only place I can think of for open loop operation.
I believe also that above about 70% throttle the PCM stops "learning" i.e. it doesn't update the long term fuel trims - not sure if it stops using the short term fuel trims though.
Regards
Paul
Re: Open loop and closed loop???? I don't think it is a case of which mode gives better performance. Neither mode has been designed as a performance mode for the PCM.
I am not an engine tuner so what I am saying could be completely wrong - take it with a grain of proverbial salt.
Anyone reading this - feel free to correct/criticise - I'm just guessing here...
Closed loop mode makes economy and emissions a priority at the expense of power.
Open loop mode *may* or *may not* make power but at the expense of economy and emissions.
I say *may* or *may not* because in open loop mode the PCM is just pushing fuel into the engine under the control of pre-determined calibrations. Those calibrations may be way out and could be hindering performance rather than enhancing performance.
I tend to look at it this way:
In closed loop mode your engine will usually run "pretty well" - it won't produce peak power all of the time but it won't run like a dog all of the time either (no offence to dogs intended).
Open loop mode - you (the tuner) need to adjust the fuel maps - if you do a better job than the closed loop adjusted fuel values you may get more power than closed loop. If you do a worse job then you will probably get less power - or worse melt your pistons.
Having said that I still believe (don't know for certain) that closed loop mode is suspended above about 70% throttle - anyone knowledgable like to help me out here? So when you need power (who needs power below 70% throttle?) you won't be in closed loop anyway. The power enrichment will override the fuel maps and you'll get the fuel you need for the power you want.
My hunch is that tuning the PE curve(s) and spark curves is where the performance can be found, which have little or nothing to do with open/closed loop operation.
Fuel curves only need to be tuned so that they are close enough to allow the fuel trims to keep everything at stoich.
Regards (and sorry if it turns out I am leading you astray)
Paul
I am not an engine tuner so what I am saying could be completely wrong - take it with a grain of proverbial salt.
Anyone reading this - feel free to correct/criticise - I'm just guessing here...
Closed loop mode makes economy and emissions a priority at the expense of power.
Open loop mode *may* or *may not* make power but at the expense of economy and emissions.
I say *may* or *may not* because in open loop mode the PCM is just pushing fuel into the engine under the control of pre-determined calibrations. Those calibrations may be way out and could be hindering performance rather than enhancing performance.
I tend to look at it this way:
In closed loop mode your engine will usually run "pretty well" - it won't produce peak power all of the time but it won't run like a dog all of the time either (no offence to dogs intended).
Open loop mode - you (the tuner) need to adjust the fuel maps - if you do a better job than the closed loop adjusted fuel values you may get more power than closed loop. If you do a worse job then you will probably get less power - or worse melt your pistons.
Having said that I still believe (don't know for certain) that closed loop mode is suspended above about 70% throttle - anyone knowledgable like to help me out here? So when you need power (who needs power below 70% throttle?) you won't be in closed loop anyway. The power enrichment will override the fuel maps and you'll get the fuel you need for the power you want.
My hunch is that tuning the PE curve(s) and spark curves is where the performance can be found, which have little or nothing to do with open/closed loop operation.
Fuel curves only need to be tuned so that they are close enough to allow the fuel trims to keep everything at stoich.
Regards (and sorry if it turns out I am leading you astray)
Paul
TECH Resident
Joined: Jan 2002
Posts: 828
Likes: 0
From: dallas,tx.
Re: Open loop and closed loop???? well said, EFIliveV5. if anyone wants a really good reference book on 82 thru 2001(2?) fuel injection systems for GM, let me recommend a book, Corvette fuel injection & electronic engine management by Charles O. Probst. this book is as valuble as any tool in your toolbox when it comes to tweaking fuel systems. it covers L83,L98,LT1,LT4,LS1,L56 & ZR-1 systems. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
Re: Open loop and closed loop???? Just got it! I'm starting to scare myself. I dig this s#!t. The book follows the descrip above.
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
Trending Topics
TECH Apprentice
Joined: Jan 2002
Posts: 384
Likes: 0
From: Murphy, TX
Re: Open loop and closed loop???? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by EFIliveV5:
<strong>Having said that I still believe (don't know for certain) that closed loop mode is suspended above about 70% throttle - anyone knowledgable like to help me out here?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">My understanding is that it's a calibration defined function of RPM as well TPS%. In my stock cal it's around 64% TPS at lower RPM and as little as 26% TPS at higher RPM. Also a "hot" curve with much lower TPS%.
<strong>Having said that I still believe (don't know for certain) that closed loop mode is suspended above about 70% throttle - anyone knowledgable like to help me out here?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">My understanding is that it's a calibration defined function of RPM as well TPS%. In my stock cal it's around 64% TPS at lower RPM and as little as 26% TPS at higher RPM. Also a "hot" curve with much lower TPS%.
