1.5T Very High Fuel Trim Reading

[PowerPerLiter]

Closed loop means the system is "closed" or looped feedback (maf,map, o2 sensor data etc) while the ecu is making adjustments.

Open loop being "open" means the looped feedback is not being factored and adjusted upon (except as you stated referencing cold start and wide open throttle). This is when the engine runs off of whatever written fuel tables it has primarily.

Why else when your doing afm adjustment would you need to make sure your reference data is collected from when the vehicle is operating in closed loop?

When writing an actual fuel table for lets say a speed density only map. You run the vehicle in open loop, make the corrections from monitored afr vs. load first within the fuel table itself and THEN you can enable closed loop to allow the car to adjust for changes in atmosphere/temp/ density altitude.

I think there are some differences in our wording or terminology. I can agree with everything you said save for the differences between open and closed loop usage. Again I think its just a differing approach of explanation.

Your correct the trims are the logged data of what the computer did to make the fueling correct and that is why we track it. To then make the adjustments wherever in the tune to prevent too much "correction". BUT where I think a key point is missing is the fact that the ecu was actively "correcting" the amount of fuel being used at every instance.

It isnt just a display of numbers while the computer does nothing to fix the fueling inside the combustion chamber at any given moment....

That would be silly for a manufacturer to provide a car with closed loop o2 sensor feedback which does nothing to correct fueling, that makes no sense.

Sponsored

 

[Gruber]

Closed loop means the system is "closed" or looped feedback (maf,map, o2 sensor data etc) while the ecu is making adjustments.

Open loop being "open" means the looped feedback is not being factored and adjusted upon (except as you stated referencing cold start and wide open throttle). This is when the engine runs off of whatever written fuel tables it has primarily.

Why else when your doing afm adjustment would you need to make sure your reference data is collected from when the vehicle is operating in closed loop?

When writing an actual fuel table for lets say a speed density only map. You run the vehicle in open loop, make the corrections from monitored afr vs. load first within the fuel table itself and THEN you can enable closed loop to allow the car to adjust for changes in atmosphere/temp/ density altitude.

I think there are some differences in our wording or terminology. I can agree with everything you said save for the differences between open and closed loop usage. Again I think its just a differing approach of explanation.

Your correct the trims are the logged data of what the computer did to make the fueling correct and that is why we track it. To then make the adjustments wherever in the tune to prevent too much "correction". BUT where I think a key point is missing is the fact that the ecu was actively "correcting" the amount of fuel being used at every instance.

It isnt just a display of numbers while the computer does nothing to fix the fueling inside the combustion chamber at any given moment....

That would be silly for a manufacturer to provide a car with closed loop o2 sensor feedback which does nothing to correct fueling, that makes no sense.

But of course it "corrects" the fueling, even does so many times a second! But a better term is "adjust" nor "correct," and this continous adjusting has nothing to do with the so called "fuel trims" known as LTFT and STFT.

There is no doubt, confusion or any vagueness about what's "closed loop." It's really a very basic and commonplace concept. What is called "closed loop" in today's car ICE engineering is the principle of all automatic control, normally called "feedback control." It just says that the controlled output variable is measured, and this signal is used to control the input variable.

[(A different system would be a feedforward control system, where the interfering input variables would be monitored, and then the input would be corrected, even before they can affect the output. This is actually what reading from tables, as in "open loop," is: for each measured set of conditions, such as: air flow, temperature, rpm, engine load, terror threat alert level.... there is a knowledge-based prescribed fuel flow value, which hopefully will produce the right AFR for these conditions.)]

"Feedback control" or "closed loop" is everywhere. That's how anything in the world is automatically controlled, including notably most temperature control. Home or car HVAC works in closed loop control - the controlled temperature is measured and this value is fed back to control the power of the heater or cooler. That's also (for just one more example) how the CD or DVD drive's optical pickup head is continuously focused on the disc. Exactly in the same way, to control the AFR for optimal ICE operation, the signals from the O2 sensors which detect the oxygen in the exhaust are fed back (via computer) to the fuel injectors . If there is very little or no oxygen, it's recognized by the PCM as a rich condition, and the fuel flow is reduced. If much oxygen, it's recognized as a lean condition, and the fuel flow is increased. By how much? No need to know by how much - keep adjusting fuel until the O2 sensor reading changes to "stoichiometric." That's all, and look - no trims needed!

These "corrections" of fuel flow happen at a high frequency and all the time. The flow of fuel is constantly adjusted, not really "corrected," many times a second. But this is the normal operation - these constant corrections are not "trims!" No need to even know air flow! In "closed loop" the fuel flow is adjusted back and forth to keep the AFR at 14.7 and there is no need for any trims - the O2 sensors keep it where it should be.

That's because these sensors essentially measure the target variable we want to control - which is the actual current AFR - so they alone can maintain exactly the stoichiometric AFR, without knowing anything else, including air flow into the engine, temperature, humidity, barometric pressure, or the current phase of the moon.

 

[Crowe]

But of course it "corrects" the fueling, even does so many times a second! But a better term is "adjust" nor "correct," and this continous adjusting has nothing to do with the so called "fuel trims" known as LTFT and STFT.

There is no doubt, confusion or any vagueness about what's "closed loop." It's really a very basic and commonplace concept. What is called "closed loop" in today's car ICE engineering is the principle of all automatic control, normally called "feedback control." It just says that the controlled output variable is measured, and this signal is used to control the input variable.

[(A different system would be a feedforward control system, where the interfering input variables would be monitored, and then the input would be corrected, even before they can affect the output. This is actually what reading from tables, as in "open loop," is: for each measured set of conditions, such as: air flow, temperature, rpm, engine load, terror threat alert level.... there is a knowledge-based prescribed fuel flow value, which hopefully will produce the right AFR for these conditions.)]

"Feedback control" or "closed loop" is everywhere. That's how anything in the world is automatically controlled, including notably most temperature control. Home or car HVAC works in closed loop control - the controlled temperature is measured and this value is fed back to control the power of the heater or cooler. That's also (for just one more example) how the CD or DVD drive's optical pickup head is continuously focused on the disc. Exactly in the same way, to control the AFR for optimal ICE operation, the signals from the O2 sensors which detect the oxygen in the exhaust are fed back (via computer) to the fuel injectors . If there is very little or no oxygen, it's recognized by the PCM as a rich condition, and the fuel flow is reduced. If much oxygen, it's recognized as a lean condition, and the fuel flow is increased. By how much? No need to know by how much - keep adjusting fuel until the O2 sensor reading changes to "stoichiometric." That's all, and look - no trims needed!

These "corrections" of fuel flow happen at a high frequency and all the time. The flow of fuel is constantly adjusted, not really "corrected," many times a second. But this is the normal operation - these constant corrections are not "trims!" No need to even know air flow! In "closed loop" the fuel flow is adjusted back and forth to keep the AFR at 14.7 and there is no need for any trims - the O2 sensors keep it where it should be.

That's because these sensors essentially measure the target variable we want to control - which is the actual current AFR - so they alone can maintain exactly the stoichiometric AFR, without knowing anything else, including air flow into the engine, temperature, humidity, barometric pressure, or the current phase of the moon.

I don't know enough about this stuff to weigh in but your explanation phrased it in a way that made something click in my head. I always felt like I was missing something when thinking about open and closed loop. Thanks for that!

Sponsored