Can someone enlighten me on Open/Closed loop. Does the 87 3.8turbo engine go into closed loop when started and when does it go in open loop. Why the difference? Do you tune in Closed or open loop. Please explain or a link that can pick me up to speed on this. Thanks
Open/Closed loop
- Thread starter Turbo85
- Start date
open loop - used before o2 sensor is heated up, ignores o2 sensor feed back for air/fuel correction. Fueling is based on look up tables in the computer.
closed loop - used after car is warmed up, relies on o2 sensor to provide feedback to computer to maintain a 14.7:1 afr
PE mode - used during wide open throttle (or near WOT). does not rely on o2 sensor feedback, but uses trends the pcm sees during part throttle use, and adds a percentage of fuel to this to drop afr to a richer mix.
I like to tune in open loop, that way I'm not fighting the PCM when adjusting the fueling tables. Once I'm done tuning, I turn closed loop back on, and burn the chip.
closed loop - used after car is warmed up, relies on o2 sensor to provide feedback to computer to maintain a 14.7:1 afr
PE mode - used during wide open throttle (or near WOT). does not rely on o2 sensor feedback, but uses trends the pcm sees during part throttle use, and adds a percentage of fuel to this to drop afr to a richer mix.
I like to tune in open loop, that way I'm not fighting the PCM when adjusting the fueling tables. Once I'm done tuning, I turn closed loop back on, and burn the chip.
Wonder if that's why the engine runs a little on the lean side upon first start up?
- Joined
- Feb 18, 2006
When the ECM goes into closed loop, it is correcting fuel to maintain a 14.7 afr ratio based on feedback from the O2 sensor. The ECM goes into closed loop after the O2 sensor and the motor (coolant) is up to temp. The ECM has the ability to add and/or subtract fuel when in closed loop. Here is where the BLM's or BL's come into play. You know how you always see everyone ask (whats your BLM's?). The BLM # tells you if the ECM is adding or subtracting fuel. 128 is the center point. No fuel is being added or subtracted. From here the BLM's can go either way. If the number climbs above 128, the ECM is adding fuel and if it drops below 128, it is subtracting. See how that works.
Generally you tune to keep the number with in 10 plus or minus 128. So between 118 and 142 is acceptable. There is a ceiling and a floor to this number. Usually 90 is the floor and 160 is the ceiling. At these points the ECM can not adjust fuel anymore. If you see your BLM hitting or resting on these numbers, you need to figure out the problem.
Dave knows what he is talking about but I think he is a little to advanced for the first timers. He can teach the open/closed loop 101 class.
Rick
Generally you tune to keep the number with in 10 plus or minus 128. So between 118 and 142 is acceptable. There is a ceiling and a floor to this number. Usually 90 is the floor and 160 is the ceiling. At these points the ECM can not adjust fuel anymore. If you see your BLM hitting or resting on these numbers, you need to figure out the problem.
Dave knows what he is talking about but I think he is a little to advanced for the first timers. He can teach the open/closed loop 101 class.
Rick
And don't forget INT's Integrators. By definition, integrator is the short term fuel trim, and BLM is the long term fuel trim. BLM and INT directly affect the injector pulse width.
Now, in speaking short term and long term these are "computer time" terms. Int. (short term) updates about 20 times per second
BLM (long term) updates about twice a second.
Functionally speaking, with a good high speed data logger you can actually see that the INT is what drives the BLM in any certain direction. You can watch this happen by doing something that might drive the BLM out of normal ops. For example, pull the vacuum hose off your fuel pressure regulator and leave it hang open. Watch the INT go a good bit higher that normal, and within just a second or two, watch the BLM start marching upward toward the INT value.
Here's the neat part, as the BLM is marching upward, you'll notice the INT start coming back down and at some point the two will "meet in the middle" as some value above 128 (or whatever value they were at when the experiment were started).
It is this rapid reaction and direct control of the injectors that make the stock computer virtually ideal for maintaining good stoicheometric A/F ratio during normal driving conditions.
It's actually amazing how tight the 14.7:1 control is in the stock ECM in normal conditions!!!
In my case I use the Translator Pro and Powerlogger and spend a lot of time experimenting with various wide band and narrow band control schemes and watching the results.
The most ideal condition that I have come up with is to allow the stock ecm to remain in closed loop (normal) narrowband O2 operations during idle/cruise/street conditions. And the wideband O2 takes over fuel control in WOT conditions when the Translator Pro switches to WOT conditions.
Geez, sorry, I didn't mean to be so long winded.
Hey, howdy DAVE H !! BTW, I'm also a Dave H
Now, in speaking short term and long term these are "computer time" terms. Int. (short term) updates about 20 times per second
BLM (long term) updates about twice a second.
Functionally speaking, with a good high speed data logger you can actually see that the INT is what drives the BLM in any certain direction. You can watch this happen by doing something that might drive the BLM out of normal ops. For example, pull the vacuum hose off your fuel pressure regulator and leave it hang open. Watch the INT go a good bit higher that normal, and within just a second or two, watch the BLM start marching upward toward the INT value.
Here's the neat part, as the BLM is marching upward, you'll notice the INT start coming back down and at some point the two will "meet in the middle" as some value above 128 (or whatever value they were at when the experiment were started).
It is this rapid reaction and direct control of the injectors that make the stock computer virtually ideal for maintaining good stoicheometric A/F ratio during normal driving conditions.
It's actually amazing how tight the 14.7:1 control is in the stock ECM in normal conditions!!!
In my case I use the Translator Pro and Powerlogger and spend a lot of time experimenting with various wide band and narrow band control schemes and watching the results.
The most ideal condition that I have come up with is to allow the stock ecm to remain in closed loop (normal) narrowband O2 operations during idle/cruise/street conditions. And the wideband O2 takes over fuel control in WOT conditions when the Translator Pro switches to WOT conditions.
Geez, sorry, I didn't mean to be so long winded.
Hey, howdy DAVE H !! BTW, I'm also a Dave H
87WE4BOOSTED
I NEED MORE BOOST!!
- Joined
- Jul 14, 2008
And don't forget INT's Integrators. By definition, integrator is the short term fuel trim, and BLM is the long term fuel trim. BLM and INT directly affect the injector pulse width.
Now, in speaking short term and long term these are "computer time" terms. Int. (short term) updates about 20 times per second
BLM (long term) updates about twice a second.
Functionally speaking, with a good high speed data logger you can actually see that the INT is what drives the BLM in any certain direction. You can watch this happen by doing something that might drive the BLM out of normal ops. For example, pull the vacuum hose off your fuel pressure regulator and leave it hang open. Watch the INT go a good bit higher that normal, and within just a second or two, watch the BLM start marching upward toward the INT value.
Here's the neat part, as the BLM is marching upward, you'll notice the INT start coming back down and at some point the two will "meet in the middle" as some value above 128 (or whatever value they were at when the experiment were started).
It is this rapid reaction and direct control of the injectors that make the stock computer virtually ideal for maintaining good stoicheometric A/F ratio during normal driving conditions.
It's actually amazing how tight the 14.7:1 control is in the stock ECM in normal conditions!!!
In my case I use the Translator Pro and Powerlogger and spend a lot of time experimenting with various wide band and narrow band control schemes and watching the results.
The most ideal condition that I have come up with is to allow the stock ecm to remain in closed loop (normal) narrowband O2 operations during idle/cruise/street conditions. And the wideband O2 takes over fuel control in WOT conditions when the Translator Pro switches to WOT conditions.
Geez, sorry, I didn't mean to be so long winded.
Hey, howdy DAVE H !! BTW, I'm also a Dave H
The LIGHT is Finally ON
87WE4BOOSTED
I NEED MORE BOOST!!
- Joined
- Jul 14, 2008
When the ECM goes into closed loop, it is correcting fuel to maintain a 14.7 afr ratio based on feedback from the O2 sensor. The ECM goes into closed loop after the O2 sensor and the motor (coolant) is up to temp. The ECM has the ability to add and/or subtract fuel when in closed loop. Here is where the BLM's or BL's come into play. You know how you always see everyone ask (whats your BLM's?). The BLM # tells you if the ECM is adding or subtracting fuel. 128 is the center point. No fuel is being added or subtracted. From here the BLM's can go either way. If the number climbs above 128, the ECM is adding fuel and if it drops below 128, it is subtracting. See how that works.
Generally you tune to keep the number with in 10 plus or minus 128. So between 118 and 142 is acceptable. There is a ceiling and a floor to this number. Usually 90 is the floor and 160 is the ceiling. At these points the ECM can not adjust fuel anymore. If you see your BLM hitting or resting on these numbers, you need to figure out the problem.
Dave knows what he is talking about but I think he is a little to advanced for the first timers. He can teach the open/closed loop 101 class.
Rick
Nice Explanation!! This page now goes in my Favorites!
Hey, howdy DAVE H !! BTW, I'm also a Dave H
And I'm also prior Navy (brown shoe though).
I'm surprised no one asked why if I do chips, I list one of Turbo Tweaks chips in my sig....
I gave up doing chips a while back when my burner died on me. I strictly do re-flashable PCM's and aftermarket engine management stuff now (for a living). There just wasn't much call for the chips anymore (thank god!)
And I'm also prior Navy (brown shoe though).
I'm surprised no one asked why if I do chips, I list one of Turbo Tweaks chips in my sig....
I gave up doing chips a while back when my burner died on me. I strictly do re-flashable PCM's and aftermarket engine management stuff now (for a living). There just wasn't much call for the chips anymore (thank god!)
This is just plain spooky!! I also used to do my own chips for quite a few years!! And gave up doing them a number of years ago.
Where are you located btw?
Im in Jacksonville, Fl
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