The fuel consumption of the car meter is inaccurate, not only because the sensor itself has errors, but even may be that the manufacturer deliberately beautified the fuel consumption of the meter.
The fuel consumption data measured by the sensor is incorrect
The fuel consumption is obtained with the fuel injection pulse width, which will produce errors over time
Most models do not have so-called fuel meters, like the leaves of our water meter turning. Mainly because if you install a flow meter on the oil circuit, it will affect the smooth flow of the oil circuit.
It’s like a small stone blocked in the water pipe, which will affect the water from the faucet, and the powerful one can’t come out. Therefore, the fuel consumption of the car is generally calculated by reading the fuel injection pulse width of the ECU and the fuel injection pressure data.
Or take the analogy of a faucet, it’s like saying you want to know how much water you use, calculate how long the faucet has been on, how much water comes out every minute, and then calculate it.
Theoretically, the fuel consumption obtained in this way is relatively accurate. But in fact, when the car is used, the fuel injection nozzle has more carbon deposits, and the actual fuel injection has an impact. At this time, the calculated fuel consumption is not so accurate.
Fuel consumption is counted by air flow, and the error is even greater
Some models of ECUs do not provide data such as fuel injection pulse width, so most third-party fuel consumption meters, such as OBD boxes, display fuel consumption using air flow data to indirectly calculate fuel consumption.
This is mainly determined based on the optimal air-fuel ratio of 14.7:1. That is, in most cases, the car sucks 14.7 parts of air, sprays 1 part of oil, and then combines some long-term and short-term fuel corrections, these data are calculated.
It’s a bit like the ratio of water and salt on a recipe is fixed, and you know how much water to put in to know how many spoonfuls of salt to put in.
A more accurate air flow meter is like a home water meter turbine type, the kind that “toot toot” will turn.
However, this flow meter will also affect the intake air, so it can only be retreated. Therefore, the bypass air mass meter with a relatively large error is the mainstream.
Mileage data also has errors
Then to calculate fuel consumption for 100 kilometers, in addition to fuel consumption data, it is necessary to know how many kilometers the car has driven. The computer is generally obtained through the ABS wheel speed sensor on the front wheel of the car.
At present, there are more used ones, called Hall wheel speed sensors and magnetoelectric wheel speed sensors. The principle is similar, there is a gear mounted on the wheel and rotates with the wheel.
Through the sensor, calculate how many teeth have turned in gear per unit time, and calculate the speed of the wheel. It’s a bit like a pedometer, which counts how many steps you’ve taken over a period of time.
Since the count is the number of steps, but how far you step forward, it does not count. This stride will affect the actual mileage.
What this stride is, is the diameter of the wheel, so the change of tire pressure, tire wear, and changing tires of different models and sizes will have a certain impact on the kilometers data.
Then some models using magnetoelectric wheel speed sensors are limited by the performance of the sensor itself, ultra-low speed or ultra-high speed, and the error will be greater than that of Hall type.
No matter what the method, there is an error in the meter fuel consumption
In general, no matter what the method, the fuel consumption of 100 kilometers shown by the car is wrong.
Even in the rigorous “Automobile Fuel Consumption Test Method”, the mileage and fuel consumption data are allowed to have a gap of 0.3% and 2% respectively.
Manufacturers may deliberately adjust
Some manufacturers will beautify the calculation method
Some manufacturers may have some beautification in the calculation method. For example, the speed is displayed instead of the actual speed.
The national standard “Automobile Speedometer” stipulates that the speed displayed on the meter must be greater than the actual speed. Therefore, using the meter to display the speed, instead of the actual measured speed to calculate, it seems that the fuel consumption of 100 kilometers will be lower.
It’s not easy to understand, it’s like eating boiled fish in a restaurant, putting the good-looking fish fillets outside, the fish bones and side dishes are placed below and don’t show you the same, a look “wow” is so hearty, a bowl of a few pieces above the pick, the bottom is like that.
For example, if the speed is 100 km/h, the actual speed is 90 km/h.
Suppose you use 7 liters of fuel in 1 hour, the apparent fuel consumption is 7 liters per 100 kilometers, but the actual fuel consumption is 7.8 liters. The deviation of 10 kilometers per hour, as mentioned above, is still allowed.
If you want to know whether your fuel consumption is reliable, fill a tank of fuel at the gas station and drive a distance.
Use GPS equipment to measure a more accurate mileage, and then go to the gas station to fill up the fuel, see how much fuel you use, divide the two data, compare your own meter fuel consumption, and immediately know.
In addition to beautifying the data, some manufacturers even exclude the parking idling and wheel speed sensors directly from the calculation when there is no data, which seems to have lower fuel consumption.
How much fuel does an hour of idle consume?
How high is the idle fuel consumption that individual manufacturers want to hide desperately? How much gasoline can be burned if this stops over there and burns oil for 1 hour? Why is such a powerful equipment and method of the Ministry of Industry and Information Technology also inaccurate?
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