What does positive long term fuel trim mean?
Positive fuel trim values 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 does Ltft B1 mean?
LTFT B1 is Long Term Fuel Trim engine cylinder Bank 1. LTFT B2 is Long Term Fuel Trim engine cylinder Bank 2.
What causes high positive long term fuel trim?
If the engine uses a mass airflow sensor (MAF), high fuel trims at idle are a classic symptom of a vacuum leak, especially if LTFT decreases at higher engine speeds. A dirty or faulty MAF sensor can also cause positive fuel trim numbers because it “under-reports” airflow, driving the base air/fuel calculation lean.
What does it mean when fuel trim is too lean?
This process is continuous: when the oxygen sensor detects too much oxygen, the PCM assumes that the air/fuel mixture is lean and adds more fuel. When there is too little oxygen in the exhaust (air/fuel mixture is rich ), the PCM reduces the amount of fuel. In technical language this adjustment is called fuel trim . What is the Fuel Trim?
How are long term fuel trims are measured?
Long-term fuel trims are measured over longer time intervals by oxygen -, or air fuel ratio sensors downstream of the catalytic converter, and in practice, the signal voltages these sensors generate are not directly implicated in fuel delivery strategies, although there some exceptions to this rule.
How does the PCM adjust the long term fuel trim?
In a long term, the engine computer (PCM) will compensate this condition by adjusting the long-term fuel trim (LTFT) to add more fuel. The long-term fuel trim is also displayed as a percentage with a “-” or “+” sign in a scan tool.
What should bank 1 fuel trim be at idle?
If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak.