HI, I was trying to get reacquainted with my ecm scanner so I was reading some guides on long and short fuel trims.
Other than not really being able to find a consistent explanation, I'm curious as to why there are two different fuel trims.
The base fuel injector map makes sense because of the oxygen sensors not being up to temp or maybe limp mode operation being needed.
As nothing is ever perfect, closed loop operation will take care of the map not being perfect or variables that cannot be controlled.
So my question is,does anyone have an insight on why there is a dual stage fuel trim design?
Purpose of two types of fuel trim?
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theKbStockpiler
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Purpose of two types of fuel trim?
Super beetle with attitude
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Bruce.m
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Re: Purpose of two types of fuel trim?
Short term trim counters errors or deficiencies in the fuel map & chases the lambda map.
Long term is an OEM trick to handle slow changes to a set up like a fuel pressure dropping by a couple of psi (regulator no longer to spec) or injector flow rates reducing slightly due to build up in the injectors. On my old BWM the long term trim was a percentage/ multiplier & the short term was a +\- adjustment
The is a Haltech video on it I think.
Long term is an OEM trick to handle slow changes to a set up like a fuel pressure dropping by a couple of psi (regulator no longer to spec) or injector flow rates reducing slightly due to build up in the injectors. On my old BWM the long term trim was a percentage/ multiplier & the short term was a +\- adjustment
The is a Haltech video on it I think.
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theKbStockpiler
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Thanks for the responce.
One of the things I read about the two different trims was that Long Term is used during open loop and Short Term is for closed.
This does make sense from an engineering viewpoint.
The Short Term Trim is said to have involvement with 'Switching' the O2 censor so the converter fluctuates from slightly too much oxygen to slightly not enough.
Its hard to get any concrete information on this subject.
This does make sense from an engineering viewpoint.
The Short Term Trim is said to have involvement with 'Switching' the O2 censor so the converter fluctuates from slightly too much oxygen to slightly not enough.
Its hard to get any concrete information on this subject.
Super beetle with attitude
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Bruce.m
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Re: Purpose of two types of fuel trim?
The Haltech video covers it.
Short term is basically EGO. It’s chasing the lambda value & doesn’t save any data. You can choose to have it oscillate around the target to improve emissions.
Long term slowly learns & stores corrections. You can set it to target slightly rich & use the short term to adjust that out (safer if the WB sensor fails)
Short term is basically EGO. It’s chasing the lambda value & doesn’t save any data. You can choose to have it oscillate around the target to improve emissions.
Long term slowly learns & stores corrections. You can set it to target slightly rich & use the short term to adjust that out (safer if the WB sensor fails)
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theKbStockpiler
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Re: Purpose of two types of fuel trim?
[quote= You can choose to have it oscillate around the target
[/quote]
Thank you for the help.
Do you recall where I could find this?
https://www.youtube.com/@haltech/videos
[/quote]
Thank you for the help.
Do you recall where I could find this?
https://www.youtube.com/@haltech/videos
Super beetle with attitude
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Bruce.m
- Posts: 1000
- Joined: Sun Aug 11, 2013 1:44 pm