What is o2 feedback trim?

Dred · 05-24-2005, 06:31 PM

Can some guru please explain what is o2 feedback trim exactly, like what it does, how it is calculated, and what effect it has on the fuel trims. All definitions I've found so far are somewhere in the lines of "1gs o2 trim should be xxx%"

Thank you very much.

4G63 GST · 05-25-2005, 02:40 AM

By feedback trim are you asking how the o2 sensor has an effect on fuel trims?

.. if so ..

o2 sensors should fluctuate between .1/.2 to .8/.9 volts on and off at idle .. the reason is they're trying to adjust the fuel ratio between rich and lean in order to even out the a/f ratio to a perfect 14.7 to 1. Since that can never happen the o2 sensor sends the voltage signal to the pcm which automatically adjusts the injector pulse .. when it sees .2 it knows there is HIGH oxygen content in the exhaust and knows the mixture is lean so it lengthens the pluse .. it then see's .9 and sees its rich and low on oxygen content and shortens the injector pulse .. ect

If you already knew that .. i just wasted 2 minutes of my life .. haha but if not i hope that helps point you in the right direction!!

Luke

Dred · 05-25-2005, 06:34 AM

Thanks, that I already k new

I understand how the o2 readings have an effect on the trims, but what is o2 feed trim or o2 trim that's in % on my logger.

Thnx for the reply tho, I appreciate you taking the time to explain

DSM90AWD · 05-25-2005, 07:44 AM

Quote:

Originally Posted by Dred

Thanks, that I already k new

I understand how the o2 readings have an effect on the trims, but what is o2 feed trim or o2 trim that's in % on my logger.

Thnx for the reply tho, I appreciate you taking the time to explain

The Long Term Fuel Trims LTFTs are the ECUs corrections to the fuel mixture as a result of the O2 Feedback in closed-loop operation over time. On 1Gs they are divided into three airflow ranges Low/Mid/High.

100% trims means the ECU percieves your mixture to be 14.5:1 so is not correcting (or just reset yoour ECU

). If you have 110% trims then the ECU thinks you are running lean so is adding in 10% more fuel for a given volume of airflow. 90% trims means you are running rich and the ECU is subtracting 10% out.

The range of the 1990 is 80-120% and 91-94 is 60-140%

4G63 GST · 05-25-2005, 01:56 PM

side note:

if your running at WOT or prolonged idle the car will go out of closed loop and go into open loop ..

Dred · 05-25-2005, 05:13 PM

Thnx guys, but what is o2 trim ?

I see a very good definition of fuel trim etc, sft and ltft I know what they are cause people define those very well. All I know about o2 trim is that it's one of the factors for correcting fuel trim(s).

spyderturbo007 · 05-26-2005, 06:20 AM

This is the only thing I could find. It is quoted from www.pocketlogger.com:

"The O2 Trim is a trim for that sensor. This allows the ECU to compensate for differences in sensors. Trims that are abnormally high or low *can* be an indication of a bad O2 sensor. o2 sensor values are ignored in open loop mode."

EDIT> I did a little searching on this and couldn't find much. Everything I did find related to boliers. But every little bit helps

O2 trim systems are added into a control system to optimize the excess air level at any point in the firing rate. When a higher or lower than desired O2 level is detected, a trim signal is sent to the air portion of the control system adjusting the air up or down within preset limits. This corrects the problem and, hopefully restores the optimum balance of air and fuel for the boiler / burner system on which it is installed. Should the O2 "error" signal be outside the preset limits, an alarm is sounded indicating a possible problem in the controls or burner.

DSM90AWD · 05-26-2005, 08:48 AM

Quote:

Originally Posted by Dred

Thnx guys, but what is o2 trim ?

I see a very good definition of fuel trim etc, sft and ltft I know what they are cause people define those very well. All I know about o2 trim is that it's one of the factors for correcting fuel trim(s).

Oxygen Feedback trim = the Short Term Fuel Trim (STFT). This is what the ECU uses to update your LTFTs during closed loop operation. It will oscillate up/down as will your O2 voltage which it should as it is directly related.

If at a certain airflow range the STFT oscillates with the mid-point at 100% then your LTFTs at that airflow range (Low/Mid/High) will approach 100%.

Remember LTFTs change over time whereas STFT is instant feedback. You can test this by logging OxyFeedback and changing the corrections on the SAFC. STFTs will change instantly, but LTFTs will eventually change to the new midpoint.

Head hurts talking techie this early in the day