What is short term fuel?
The short-term fuel trim (STFT) refers to immediate changes in fuel occurring several times per second. So, for instance, if you start going up a hill and need more fuel, if a vacuum line comes off and creates a lean condition, or if there is any airflow/fueling change in the moment, the STFT is there to assist.
When to use short term and long term fuel trims?
If you connect a scan tool to such a vehicle, both the short and long-term fuel trim data will be displayed as percentages. Ideally, both values should be at, or close to 0%, when the engine is running at a steady speed, such as when it is idling.
What is long term fuel trim on scan tool?
Long term fuel trim at 7.8% is a strong clue. The Air Fuel Ratio (A/F) sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the…
What causes fuel trim values to be off?
However, even if the sensors are known to be good, it can happen that displayed fuel trim values may be off by as much as 20% or more; this can be the result of a malfunction, or, it can be the result of someone having recently cleared all fault codes.
If you connect a scan tool to such a vehicle, both the short and long-term fuel trim data will be displayed as percentages. Ideally, both values should be at, or close to 0%, when the engine is running at a steady speed, such as when it is idling.
What does it mean when fuel trim data is failing?
In this example, the fuel trim data was failing in both banks and every operating range—idle speed, light load, moderate load and heavy load—which means the lean condition was present in all driving conditions. What are your thoughts about an intake air leak now?
Can a fuel trim of 10% increase fuel delivery?
A total fuel trim of 10% will increase fuel delivery with 10% and a total fuel trim of -10% will decrease the fuel delivery with 10%. If any of the value exceed 25% or beneath -25% then the check engine light is turned on with a number of error codes, which can be read using an appropriate scan tool.
Long term fuel trim at 7.8% is a strong clue. The Air Fuel Ratio (A/F) sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the…