When to turn off long term fuel trims?
However, when long-term fuel trims exceed about 10% or so to either side of 0%, there is a problem that needs to be investigated, but note that codes indicating rich or lean running conditions will generally only be set when the deviation reaches about 25% or so.
How does the PCM adjust the long term fuel trim?
In a long term, the engine computer (PCM) will compensate this condition by adjusting the long-term fuel trim (LTFT) to add more fuel. The long-term fuel trim is also displayed as a percentage with a “-” or “+” sign in a scan tool.
Is there such a thing as a 0% fuel trim?
While fuel trim values of 0% would be ideal, there is no such thing as a perfect engine, which means that in practice, achieving 0% fuel trim values consistently gets progressively more difficult as an engine ages.
What are the fault codes for fuel trim?
Fig. 1 above shows the fuel trim data collected on a vehicle with the Check Engine light on and fault codes P0171 (Bank 1 System Lean) and P0174 (Bank 2 System Lean) present.
However, when long-term fuel trims exceed about 10% or so to either side of 0%, there is a problem that needs to be investigated, but note that codes indicating rich or lean running conditions will generally only be set when the deviation reaches about 25% or so.
While fuel trim values of 0% would be ideal, there is no such thing as a perfect engine, which means that in practice, achieving 0% fuel trim values consistently gets progressively more difficult as an engine ages.
What are the four ranges of fuel trim?
2. Monitor and record the fuel trim values in the four common operating ranges—idle speed, light load (20 to 30 mph), moderate load (40 to 50 mph) and heavy load (60 to 70 mph). 3. Analyze the collected data.
Fig. 1 above shows the fuel trim data collected on a vehicle with the Check Engine light on and fault codes P0171 (Bank 1 System Lean) and P0174 (Bank 2 System Lean) present.