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UltraGauge
Blue
™
User Manual www.ultra-gauge.com
Fuel Trim
Gauge name
Range
Units
Abbreviation
Short fuel trim bank1
-100% to 99.2%
Percent of
typical
sFT B1S1
Long fuel trim bank1
lFT B1S1
Short fuel trim bank2
sFT B2S1
Long fuel trim bank2
lFT B2S1
Fuel trim refers to the fine tune control of fuel delivery and specifically indicates adjust ments
made dynamically to the base fuel table to obtain the proper ratio of fuel to air. The fuel-to-air
ratio is adjusted by increasing or decreasing the time fuel injectors are open. Note that fuel
injectors are either fully open or fully closed - there is no variable opening.
Fuel trim is generally calculated by using a wide set of data values, including forward O
2
sensors, intake air temperature/pressure or air mass sensor, barometric pressure, humidity,
engine coolant temp, anti-knock sensors, engine load, throttle position , and battery voltage.
Short term fuel trim refers to adjustments being made in response to temporary short term
conditions.
Long term fuel trim is used to compensate for issues that seem to be present over a much longer
period or that are essentially permanent. Long term fuel trim generally should not -
10% in most vehicles.
Fuel trims are expressed in percentages with a range of -100% to 99.2% of nominal. Positive
values indicate a lean condition exists and the injector is left open longer to compensate, thus
adding more fuel. Negative values indicate a rich condition exists and the injectors are closed
more quickly thus reducing the amount of fuel.
Example: A value of 5.0% indicates that the injector is being left open 5% longer than normal,
thus the fuel to air ratio is being increased.
Fuel trim could more appropriately be called “Injection on-time %”.
Fuel trim banks refer to the cylinder banks in a V style engine. Cylinder #1 is always in bank 1.
Even though the engine may contain two physical banks, only a single bank may be reported by
the ECU. UltraGauge displays Fuel Trim Banks One and Two if reported by the vehicle’s
engine computer. For those vehicles with three or four banks, only banks one and two will be
available for display on UltraGauge.
UltraGauge supports the following Fuel Trim Gauges:
Short Term Fuel Trim percentage Bank 1
Short Term Fuel Trim percentage Bank 2
Long Term Fuel Trim percentage Bank 1
Long Term Fuel Trim percentage Bank 2
NOTE: If the engine is operating in Open Loop, the short trim will be reported as 0%.
