LTFT B1 normal range points to the range vehicles trim fuel. For an engine to work optimally, there must be appropriate air-fuel mixture, and this is what fuel trim helps to accomplish. Fuel trim optimizes engine performance by ensuring the engine gets only the fuel needed.
The engine computer works with various sensors(MAF and O2 sensors) to know how much air goes into the engine. It then uses the data and the estimated air-fuel ratio to determine how much fuel to push into the engine. If the estimated fuel ratio is too much or too little, it trims by adding or subtracting. Fuel trims are recorded in two ways, —LTFT and STFT.
What is Long-Term Fuel Trim (LTFT)?
Long-term fuel trim is the record of what the engine controller (ECM/PCM) has been doing over a long period to balance air fuel-ratio. It does this by collecting information about the air in the engine via the downstream oxygen sensors and balancing it by subtracting or adding fuel.
LTFT values generally take a few seconds to update and are stored in the engine’s computer memory.
Short-term fuel trim (STFT), on the other hand, is the current record of how the engine computer trims fuel to balance the air-fuel ratio. This reading usually fluctuates since different conditions, such as engine speed, load, temperature, and other operating conditions, influence the engine.
Unlike LTFT, STFT uses the upstream O2 sensors. More so, its values update every few seconds and are not stored permanently in the engine computer. With the engine computer effectively trimming fuel, all issues related to incorrect air-fuel ratio are settled, ultimately leading to better engine performance.
What is a good long-term fuel trim reading?
Fuel trim reading can be positive or negative, whether STFT or LTFT. But generally, a good long-term fuel trim reading should be between -10 and +10. You can also say the same for short-term fuel trim. So, for those asking, what is the short-term fuel trim normal range or long-term fuel trim normal range? There you go:
It is worth noting that the ideal fuel trim value, whether for LTFT or STFU, is 0 but can also range from -10 to +10. These values are a good indicator of how the fuel mixture is corrected to compensate for changes in air-fuel ratio inside the engine.
With the negative indicating the engine computer is subtracting fuel, the positive sign shows the engine is adding fuel. So, if your fuel trim values are above or below these, something is wrong with the system.
It could be the engine, sensors, or fuel delivery system. Fuel trims are read by connecting an OBD II scanner or any scan tool to your vehicle’s OBD II port. More so, ensure the car is up and running when reading your fuel trim so you can get a good reading. It’s worth noting that some engines can have two sets of STFT or LTFT readings because of the number of cylinders.
The engine controller (ECM/PCM) trims fuel using the information it gets from the O2 sensors. And for engines like V8 and V6, one sensor is used per cylinder bank. So, the engine computer will trim fuel based on the information from the sensor in each cylinder bank. Thus, the discrepancies happen in readings.
But even if they get different readings, they should always be between -10 to +10. When a long-term fuel reading gets too large, say -25 to +25, the engine computer will trigger the MIL, prompting some fault codes between P0170-P0175 to show. With these codes, one can easily tell what is causing the fuel issues and fix them.
What does negative LTFT mean?
Negative LTFT indicates that, over time, the engine computer has been sending less fuel to the engine to balance the air-fuel ratio. The computer could start supplying less fuel if it perceives the engine is running too rich.
An engine could run rich if too much fuel or less air is entering the engine. To lean out the mixture, it reduces the rate at which the engine sends fuel to the engine by decreasing the speed or time at which the fuel injectors send fuel.
And if your engine controller has, over time, been adding more fuel, your LTFT will show a positive value. Generally, an engine computer sends more fuel if it detects a lean mixture (too much air or less fuel). To, therefore, balance the mixture, the engine compensates by sending more fuel.
The ECM or PCM uses both fuel trims to correct the system by ensuring the engine gets only the fuel needed to work efficiently. Fuel trim information can also help technicians know the cause of an engine problem. For example, if the trim value is too high, say around +25, the technician knows the engine is taking too much fuel and looks for possible culprits.
Why is my long-term fuel trim negative?
Your long-term fuel trim is negative because your engine controller, over time, has been pushing in less fuel for combustion. It does this when it notices that the engine needs less fuel than initially estimated, probably because it runs rich.
Your long-term fuel trim showing negative shouldn’t be an issue, as the engine computer also uses it to balance the fuel mixture needed for combustion. What you should be worried about is the exact negative value it shows. Values between -1 and -10 are acceptable.
However, if you have a larger negative value, say -25, the engine is getting far too less fuel and needs to be addressed immediately. As this could hamper vehicle performance and increase emissions and fuel consumption. Possible culprits are a leaky intake manifold, fuel injector stuck open, clogged air filter, etc.
What is the normal LTFT B1 range?
The LTFT B1 range refers to the percentage of fuel trim over a long period of time for cylinder bank 1. The normal LTFT B1 range should be 0 or numbers near 0 if all components work fine in a normal engine working condition. However, the value can fluctuate since vehicles don’t move at a constant speed.
For example, while LTFT B1 normal range at idle could be close to 0, it should return to zero once the vehicle regains steady speeds. More so, these fluctuations should not be too rampant; if the values fluctuate like a STFT, there is an issue. If the sensors work correctly, the LTFT B2 normal range should also be 0 or near 0.
Wondering what B1 and B2 mean? Here you go. B means bank and represents each cylinder in your engine. With B1 standing for bank 1, that is the number one cylinder bank, B2 stands for bank 2 cylinder.
To therefore explain LTFT B1 meaning, it is the long-term fuel trim value on cylinder bank 1. What about the STFT B1 meaning? This indicates the short-term fuel trim value on cylinder bank 1.
While the LTFT B1 normal range should be 0 or close to it can fluctuate when the engine is not operating at a constant speed. However, it should return to zero when the engine is at a steady speed. Fluctuations when the engine is at a steady speed may indicate a problem with the engine, the sensors, or the air or fuel delivery system.
For optimal fuel trims, the computer needs an accurate reading from the O2 sensor to know if the engine is running lean or rich. Faulty O2 sensors, however, will cause the computer to trim wrongly, leading to wrong fuel trim information. To avoid this, ensure your oxygen sensors are in good shape.