What should STFT be at idle?
Ideally, the STFT and LTFT should be within a few percentage points of zero when the engine is idling or being held at a steady RPM. Remember, STFT can bounce around quite a bit as when you suddenly snap open the throttle or decelerate.
What should STFT be while driving?
When everything is stable and working correctly, fuel trim numbers should be no greater than 10%, and total fuel trim should be no more than 10% when the numbers are added together. For example, if LTFT is 4% and STFT is 4%, the total is 8%: that’s acceptable.
What does STFT B1 mean on a code reader?
STFT B1 is Short Term Fuel Trim engine cylinder Bank 1.
What is normal STFT?
A normal STFT reading will generally fluctuate quite frequently, so don’t be surprised to see it as positive one second and negative the next. Usually, they’ll stay within %5 +/- of zero. On an older engine, they may go up towards 10% at times.
What causes high STFT?
High STFT are usually caused by a vacuum leak or a bad MAF.
What should my O2 sensor read?
A properly functioning oxygen sensor will show a rapidly fluctuating output voltage between approximately 0.1 and 1.0 volts. The time taken for the voltage to change from 0.1 V to 1.0 V (referred to as the lean to rich response time) should be about 300 milliseconds.
How do I reset my short term fuel trim?
This is done by disconnecting the battery, waiting for 10 minutes or so, and/or turning the ignition key to the starter position to discharge the system. Note, the code “Erase” button on scanners does not reset the LTFT, at least not on my S70.
Why is my short term fuel trim high?
If the displayed fuel trim value is a positive number, it means that the ECU is increasing the injector pulse width to add fuel to the air/fuel mixture to enrich the mixture because the input data it is receiving tells it that the mixture is too lean.
What causes high fuel trims at idle?
During idle when the throttle plate is closed, the vacuum in the intake manifold is high and very little air flow is entering the engine, so even a small amount of un-metered air will have an effect on fuel trim. This forces the PCM to react to the lean condition with positive valued fuel trim readings.
What does Stft B1 S2 mean?
Those are the catalyst monitors see where it says B1 S2 that means bank 1 sensor 2 you want to see a high % there as it shows no unburned fuel air/gas coming out. STFT is mainly relevant for B1 S1 and B2 S1 and that will vary depending on how well the engine is running.
What should fuel trim numbers be?
So what should fuel trim values be? Assuming that the engine is in excellent mechanical condition, and that all sensors implicated in metering both intake air and fuel, short-term fuel trim values should generally be between positive 10%, and negative 10% when the engine is running at a steady speed.
What is STFT B1 S2?
How do you relearn fuel trim?
When should I reset fuel trims?
Any time you’re tuning VE or MAF, you should force open loop and disable the open loop STFT. After that, flash the file, start the engine and reset the trims.
What should my o2 sensor read?
What is the STFT of a positive STFT?
Not only are the STFT’s positive (they are usually around +2.0% to +4.0%), but they are also very close to each other.
What does a significant increase in STFT or LTFT mean?
A significant increase in STFT or LTFT from 0% means the ECU is detecting more air than expected and is adjusting fuel delivery with more fuel. A significant decrease in STFT or LTFT from 0% means the ECU is detecting less air than expected and is adjusting fuel delivery with less fuel.
What do normal STFT values look like?
To me STFT values look normal, they don’t vary that much, they are close to 0.0 in low RPMs, and they are usually equal with slight variation. Here is what I have done:
What does it mean when LTFT is 0%?
LTFT and STFT will usually stay close to 0%, which equates to no adjustment. However as the engine wears, the adjustment will be necessary. A significant increase in STFT or LTFT from 0% means the ECU is detecting more air than expected and is adjusting fuel delivery with more fuel.