What should the short term fuel trim 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.
Where is short term fuel trim?
Short-term fuel trim (STFT) This is necessary for the catalytic converter to do its job correctly, and the average of the rich/lean swings will be in or near the middle of the oxygen sensor’s signal range. You can see this by displaying graphs of equivalence ratio, the oxygen sensor and STFT on a scan tool.
How does short term fuel trim ( STFT ) work?
Short Term Fuel Trim (STFT) Short-term fuel trims occur as a direct result of changes in the oxygen content of the exhaust stream. The exhaust stream is monitored by an oxygen sensor upstream of the catalytic converter, and the signal voltage it generates is directly proportional to the oxygen content of the exhaust stream.
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.
What causes short term and long term fuel trims?
In practice, the ECU manages two distinctly different types of fuel trims, these being- Short-term fuel trims occur as a direct result of changes in the oxygen content of the exhaust stream.
When to use fuel trim to identify a problem?
Fuel trim can also be used to identify which bank of cylinders is causing a problem. If the LTFT for bank 1 is 20% and the LTFT for bank 2 is 3%, the source of the problem is associated with bank 1 cylinders only.
What causes negative fuel trim?
A negative fuel trim is considered anything at or below the minus 10 percent threshold. Ron addresses the common issues that can cause fuel trims to go negative. Issues like leaking fuel injectors, a defective fuel pressure regulator and defective MAF sensors will be addressed.
What is long term fuel trim?
Long-term fuel trim refers to the measurements these sensors make , which are effectively an average of the modifications the ECU made as a result of short-term fuel trim. That Sounds Like A Ton Of Data.
What is a positive fuel trim?
POSITIVE fuel trim values mean the engine computer is adding fuel (increasing the pulse width or on-time of the fuel injectors) to add more fuel to the engine. In other words, it is attempting to RICHEN the fuel mixture because it thinks the engine s air/fuel mixture is running too lean.
What are fuel trims all about?
In short, fuel trim describes the adjustments that a vehicle’s engine control unit (ECU) makes to the fuel delivery system to keep the air-fuel mixture as close to its ideal ratios as possible. Short-term fuel trim happens as a result of changes in the oxygen levels of exhaust gases.