Flowmeter: What Is It? How Does It Work? Why Can It Be Damaged?

A flowmeter ensures that our car's engine works properly, that the ignition spark is perfect, that the mixture of air and fuel is optimal to offer maximum performance and, at the same time, generate the least amount of polluting waste. Also known as MAF (for Mass Air flow Sensor ) it is one of the key components of an electronic fuel injection system in any car with a traditional engine.

According to the Red Operativa de Desguaces Españoles (RO-DES) , the flowmeter is also known by the name of debimeter , and consists of an electronic device "responsible for measuring the mass of air that enters the intake manifold from the outside” and to send this information to the brain of the car. The flow meter is present in diesel and gasoline cars , at the air filter outlet and on the intake pipe. Thus, the path that the air must travel is already filtered to reach the cylinders and start the combustion process.

How does the flowmeter work?

The flowmeter has a small wire that is electrically heated (hot wire). A temperature sensor installed near that cable measures the temperature of the surrounding air. When the engine is idling, a small amount of air flows around the cable, so a very low electrical current is needed to keep it at a temperature of 120º C). The moment you step on the throttle, more air flows over the hot wire. That passing air cools the wire, and the more air that flows through it, the more electrical current is needed.

The electrical current is proportional to the amount of airflow. A small electronic chip installed inside the flowmeter sensor translates the electrical current into a digital signal and sends it to the brain of the engine. The control unit (ECU) uses the signal from the flowmeter to calculate the amount of fuel to be injected into the cylinders. The goal is to keep the air-fuel ratio at the optimal level. The ECU and flowmeter work hand in hand making hundreds of decisions per second to adjust the mixture.

Also, on vehicles equipped with an automatic gearbox , the ECU uses readings from the flow meter to determine when to shift. If the flowmeter is not working properly, the transmission may also be working differently .

How do I detect problems in a damaged or defective flowmeter?

Problems with flow meters are common in many vehicles, and most of the time it is because the sensor could be contaminated or damaged . For example, on some engines, a faulty flowmeter could cause us to start, but not be able to move. A poorly installed or clogged air filter also helps the flowmeter fail sooner, or get it too wet (even if it is washable).

A bad flowmeter cannot measure the amount of airflow correctly . This causes the ECU to miscalculate the amount of fuel injected, which can cause everything from jerks when accelerating that we didn't feel before, until it simply decides not to inject any fuel into the cylinders; Consequently, we will not be able to move forward. Normally, when a flowmeter does not work as it should, the engine fault warning light comes on or the annual service message (or by engine, if it is modern) appears on the instrument panel.

Some of the most common failures that we will notice in case of having a faulty or broken flowmeter are:

  • jerks
  • a slow acceleration
  • No response to throttle demands
  • Black smoke coming out of the exhaust pipe
  • worse fuel efficiency
  • rough idle
  • It is difficult to start (and it is not a problem with the alternator, battery or starter motor)
  • Engine fault warning light or service message
  • Types of flowmeters

Mechanical systems: these flowmeters come with a butterfly valve in the empty space of the collector when they are responsible for letting the air in as it is sucked into the combustion chamber.

Electronic injection systems: in this type of flow meter, the sensor sends the measurements to the ECU so that it knows how much fuel it needs to inject for optimal combustion. In addition, this system is also responsible for activating the exhaust gas recirculation systems, such as the EGR valve .

What maintenance does a flowmeter need?

As mentioned above, the air filter can help lengthen or shorten the life of a flowmeter. The function of this component is to clean the air that comes from the outside so that it reaches the engine as pure as possible and carries out correct combustion. However, if it becomes clogged by excess dirt, it will not allow the correct passage of the necessary amount of air. For this, it is advisable to replace the air filter between 10,000 and 15,000 kilometers depending on the use and the type of roads on which we circulate.

On the other hand, if the crankcase oil is in good condition, it helps with a good flowmeter operation. This is due to the fact that the oil gases that come from the crankcase and are recovered in the intake could also damage the flow meter. Likewise, carbon is another of the problems that can affect the sensor, which normally appears due to driving at low rpm on a regular basis in a diesel (especially in the city). Humidity could also affect the flowmeter, and although it is less likely, on the coast it is not impossible.