What should short term fuel trim read?
With the engine idling, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range may be high as plus or minus 8, but closer to zero is best. If the numbers are +10 or higher for STFT and LTFT, your engine is running LEAN.
What causes high short term fuel trim?
Short-term fuel trim happens as a result of changes in the oxygen levels of exhaust gases. An oxygen sensor monitors the flow and generates a signal that is proportional to the oxygen levels in the gases.
How do I reset my short term fuel trim?
To perform a PCM reset…
- Bring car up to normal operating temp.
- Turn ignition off.
- Remove ECM main fuse.
- Turn ignition to “on”, do not start.
- Wait for system check to complete, numerous errors will be detected.
- Turn ignition off.
- Replace fuse.
- Turn ignition to “on” and wait for system check.
How long does it take long term fuel trim to adjust?
five to 20 seconds
In general, it takes anywhere from five to 20 seconds for LTFT to change, and since it’s stored in memory when the engine is switched off, that same LTFT value is used next time the system goes into closed-loop operation.
What makes the short term fuel trims all about?
Really, the oxygen sensors are what drive the fuel trim readings. Changes in o2 sensor voltages cause a direct change in fuel. The short term fuel trim (STFT) refers to immediate changes in fuel occurring several times per second. The long term fuel trims (LTFT) are driven by the short term fuel trims.
When do fuel trim readings return to normal?
This forces the PCM to react to the lean condition with positive valued fuel trim readings. The fuel trims will return to almost normal during cruise and wide-open throttle when the throttle plate is open and there is little vacuum in the intake but lots of air flow into the engine.
What is the adaptive strategy for fuel trim?
Fuel trim’s adaptive strategy consists of two components: short-term fuel trim (STFT) and long-term fuel trim (LTFT). In the European world, these terms are known as additive for STFT and multiplicative for LTFT.
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.