Help with short and long term fuel trims

s300 and SManager software questions & answers
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TheLawProject
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Joined: Sat Apr 04, 2020 1:43 pm

Help with short and long term fuel trims

Post by TheLawProject »

Can someone please clarify how the short and long term fuel trim works while in closed loop. I have tuned my fuel tables in Open loop with an AEM wide band and they are spot on. When I switch over to Closed Loop (lambda target) the short term is correcting +/- 3% and the long will eventually show 1% +\- after some driving. After about 20-30 minutes of driving the S. Trim seems to freeze and is no longer reading or correcting. Is this normal?

Secondly while in closed loop (lambda target) after about 20-30 minutes of driving I get a check engine light for the o2. Sign of a faulty o2?

Thank you!!
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Spunkster
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Re: Help with short and long term fuel trims

Post by Spunkster »

What wideband are you using and how do you have it connected?
TheLawProject
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Re: Help with short and long term fuel trims

Post by TheLawProject »

AEM x-series wideband connected to D10.
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Spunkster
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Re: Help with short and long term fuel trims

Post by Spunkster »

Post your calibration as well a datalog showing the issue.
TheLawProject
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Re: Help with short and long term fuel trims

Post by TheLawProject »

Here is my latest Calibration. I do not have a data log to go with it to show the short term trim stop working. I can get that tomorrow.
Attachments
New Calibration Closed Loop Lambdatarget loop, IAT on, Winter tune with IAT fuel comps 4-1-21.skl
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TTR
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Re: Help with short and long term fuel trims

Post by TTR »

I have the same setup in my car. Running closed loop off the AEM. Mine works indefinitely. (dumb question) Does the wideband still show A/F after the short term stops working? I have noticed on multiple cars that the analog output on these widebands aren't very consistent. My output comes on about 20-30 seconds after the gauge is powered up. I have have had customers come on only when the engine is cold (doesn't make sense) and will not come on hot. Some have never worked. I asked AEM years ago and they told me it should come on right away, the typical answer, we've never heard of this before. I'd back probe the output and make sure there is actually voltage on the output when the short term stops working. It could also be the ecu.
TheLawProject
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Joined: Sat Apr 04, 2020 1:43 pm

Re: Help with short and long term fuel trims

Post by TheLawProject »

The AEM reads an AFR if it’s in open or closed loop. It continues to read even when the S. term Trim stops showing corrections. When it is in Closed loop and the S. term trim is showing corrections, the AEM reads very quickly and the AFR’s swing from 14.4-15.0 back and forth back and forth. Then once the s. term stop working it the AFR settles down and seems to read more consistent but is I little rich around 14.3/4.

Again when in closed, after 30mins or so of driving it will always throw a check engine code for o2 sensor.

When in Open loop none of this happens.
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