To discharge the system, disconnect the battery, wait for about 10 minutes, and/or turn the ignition key to the starter position.
In This Article...
How long does the long-term fuel trim take to adjust?
The time it takes for LTFT to change typically ranges from five to twenty seconds, and since it is saved in memory when the engine is turned off, the same LTFT value is used the following time the system enters closed-loop operation.
What should the fuel trim be over the long term?
While 0% fuel trim values would be ideal, since there is no such thing as a perfect engine, it is actually becoming more and more challenging to maintain 0% fuel trim values as an engine ages. Although current ECUs are engineered to account for higher oil consumption rates, sensors losing sensitivity, and other factors that effect fuel trims, fair wear and tear on engines cannot be avoided. As a result, bear the following in mind when interpreting fuel trim values:
When the engine is running at a constant speed, short-term fuel trim values should typically range between positive 10% and negative 10%, assuming that the engine is in great mechanical condition and that all sensors involved in metering both intake air and fuel are functioning properly. However, keep in mind that all fuel trim values should be obtained at a minimum of three consistent engine speeds: idle, around 2500 RPM, and approximately 3500 RPM. This is because rapid fluctuations in the engine speed can cause short-term fuel trim values to fluctuate drastically. Also keep in mind that fuel trim measurements must be made after the engine has ran at the aforementioned speeds for at least 30 seconds.
When the engine is running at a constant speed, long-term fuel cuts should be at or almost at 0%. The long-term fuel trim value will (and must) change as the engine speed changes, but as soon as the engine speed stabilizes, this value should go back to a value near to 0%. Remember to suspect a faulty catalytic converter if the long-term fuel trim values change in a manner similar to the short-term fuel trim values.
As a general rule, however, long-term fuel trim readings that are in the 5 to 8% range, whether positive or negative, are not always a sign of a problem. Note that codes indicating rich or lean running conditions will typically only be set when the deviation reaches around 25% or so. However, when long-term fuel trims approach about 10% or so to either side of 0%, there is a problem that has to be investigated.
On the other hand, while the engine is running at a steady speed, short-term fuel trim readings frequently fluctuate by as much as 10% on either side of 0%, which is not always a sign of a problem. A rich or lean running trouble code will almost always appear if the deviation exceeds about 25% while the engine is operating at a steady speed, indicating that there is a problem.
What creates long-term fuel trim that is favorable?
The fuel feedback control system is making up for an air/fuel mixture that is progressively becoming leaner over time if the LTFT fuel trim values are moving up (POSITIVE). Clean fuel injectors would be the most likely culprit.
When should the fuel trims be reset?
Force open loop and turn off the open loop STFT whenever you’re fine-tuning VE or MAF. Flash the file after that, then turn on the engine and reset the trims.
Does fuel trim depend on downstream O2 sensor?
Oxygen (O2) sensors serve two crucial purposes as a component of the engine management system. While the downstream O2 sensor(s) monitor the catalytic converter, the upstream O2 sensor(s) in the exhaust manifold(s) monitor the air/fuel mixture (s).
The majority of O2 sensors are of the switching variety, which produce a rich or lean voltage signal based on how much oxygen is present in the exhaust unburned. A few, such as the “titania O2 sensors” in some vintage Nissan, Toyota, and Jeep applications, vary resistance to signal a rich or lean exhaust situation. The fuel mixture is monitored by a “Air/Fuel sensor,” which is actually a “broad band O2 sensor, in many late-model applications.
The Powertrain Control Module (PCM), the engine computer, takes the input from the upstream O2 sensor(s) to alter the fuel mixture as necessary for the best emissions, fuel efficiency, and performance. To detect any converter issues and to fine-tune fuel trim, the downstream O2 sensor(s) is/are used as input.
The OBD II system ought to recognize any issues with an O2 sensor, its internal heater, or wiring circuit, set one or more error codes, and illuminate the Check Engine light. The sensor needs to be replaced if diagnosis reveals a defective sensor (and not a wiring issue or another type of engine issue that is affecting the sensor reading).
In a high-mileage car with a V6 or V8 engine, if one upstream O2 sensor fails, there is a good likelihood that the second upstream O2 sensor on the opposing cylinder bank is also nearing the end of its useful life. It is advised to replace both sensors in order to get performance and fuel efficiency back to normal.
Due to their location behind the converter and less heat exposure, downstream O2 sensors often have a longer lifespan. On the other hand, their undercar placement makes them more susceptible to corrosion and road splash. Therefore, if the catalytic converter is being replaced, a new downstream O2 sensor ought to be installed.
There are two types of replacement oxygen sensors: precise fit and universal. precise fit O2 sensors hook into the engine wiring harness similarly to the original sensor and come complete with a wiring harness and connector. Since there is no need for wire cutting or splicing, exact fits are quick and simple to install. On the other hand, universal O2 sensors do take a little more installation work but allow for fewer part numbers to enable far wider application coverage.
What results in a negative long-term fuel trim at idle?
The negative fuel trim values are brought on by the MAF sensor’s overestimation of airflow at idle. It then overestimates airflow at cruising speeds, which explains why fuel trim figures are positive.
How can you know if an oxygen sensor is malfunctioning?
Symptoms of a Faulty Oxygen Sensor
- Check engine light that is illuminated. If you have a malfunctioning oxygen sensor, your dashboard’s bright orange Check Engine light will often glow.
- poor gas mileage
- A rough-sounding engine
- Failure of the Emissions Test.
- a more aged vehicle.
What sensors are involved in fuel trim?
The accuracy of the computer’s fuel trim technique is monitored by the oxygen sensors. The oxygen sensor measures the amount of unburned oxygen present in the exhaust and is situated inside the exhaust. This shows the integrity of the fuel mixture.
How is fuel trim affected by a vacuum leak?
Lean exhaust codes P0171 and P0174 are frequently caused by vacuum leaks. The high fuel trim correction that exceeds a preset limit is the cause for the PCM setting these lean codes. Depending on the application, a higher fuel trim number will cause these codes to set.
The fuel trim correction is impacted by vacuum leaks at idle, but when engine load and RPM rise, the fuel trim corrections return to normal. Figure 1’s graph illustrates how fuel trim adjustments function in the presence of a vacuum leak.
The amount of air that enters the engine through the vacuum leak when the throttle plate is closed accounts for a sizeable portion of all air entering the engine. In order to compensate, the computer must richen the mixture, forcing fuel trim positive.
Engine RPM rises as the throttle opens because more air enters via the open throttle plate than when it is closed. Therefore, the amount of air entering the engine through the vacuum leak decreases significantly. As a result, during running with the throttle open, fuel trim adjustments can return completely to normal.
The engine’s capacity to breathe is unaffected by vacuum leaks, therefore an engine with one would still have standard volumetric efficiency ratings.
What two factors can result in a lean mixture?
When the ratio of air to fuel is higher than it should be, the mixture is said to be lean. When this happens, your engine will probably still function, but the mechanics of the combustion engine will jerk, which will eventually cause damage to the engine, such as burned valves.
As an alternative, one of the following is probably to blame for your engine running lean:
- inadequate fuel
- incorrect pump regulator
- inadequate fuel pressure
- The position of the EGR valve is stuck open.
- an air leak
Describe long-term fuel trim bank 1.
Fuel trim, in its simplest form, refers to the modifications an engine control unit (ECU) makes to the fuel delivery system to maintain the air-fuel mixture as closely as possible to optimal ratios.
Short Term Fuel Trim
Changes in the oxygen content of exhaust gases lead to short-term fuel trim. An oxygen sensor keeps track of the flow and produces a signal that is proportionate to the gases’ oxygen content. The ECU will respond and make adjustments right away in a system that is operating properly as the exhaust gases change. Because of this quick response, it is referred to as short-term.
Long Term Fuel Trim
Sensors located further downstream in the exhaust system, after the catalytic converter, are used for long-term fuel trimming. The signal at the sensors further down should be pretty consistent, whereas the signal upstream, where short-term fuel trim is recorded, would fluctuate regularly. The measurements taken by these sensors, which are essentially an average of the changes the ECU made as a result of short-term fuel trim, are referred to as long-term fuel trim.
What are fuel trims, and how do you operate them?
The engine control system uses fuel trims to account for any issues with air-fuel ratios (often referred to as lambda) and combustion.
A few sensors are used by the Electronic Control Module (ECM) or Powertrain Control Module (PCM) to measure the amount of air entering the engine. The amount of fuel to inject is then determined using the airflow data and a target air-fuel ratio (or lambda). The ECM or PCM then “trims” the fuel quantities based on the “real” air-fuel ratio by using oxygen sensor readings to determine what the actual air-fuel ratio was.
With the help of the oxygen sensor, the PCM/ECM can determine whether the calculated amount of fuel required is too much or too little, at which point it will ‘trim’ the amount of fuel to improve combustion. Fuel trim is the difference between the calculated and actual amount of fuel being delivered to the cylinders. Long-term fuel trim (LTFT) and short-term fuel trim are the two main ways fuel trim is reported (STFT).
What is Bank 2 of the long-term fuel trim?
The meaning of the diagnostic problem code (DTC) P0173 is “Fuel Trim Bank 2.” This error message signifies that the fuel trims in your car are no longer functional (maximum rich or maximum lean). Fuel trim refers to the ongoing adjustments that the PCM makes to the fuel mixture to keep the air-fuel ratio balanced.
How can I tell if my oxygen sensor is malfunctioning upstream or downstream?
A drop in fuel economy may be a clear indication that an O2 sensor is not functioning properly. A gasoline combination that is either too low or too rich can produce this. A/F ratio swings of this magnitude indicate a malfunctioning upstream or control sensor.