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Fuel consumption, rough idling: Getting the right MAF or O2 sensor

Excessive fuel consumption, stalling, rough idling and check engine light are some of the symptoms when a car has either a bad Mass Airflow Sensor, Heated Oxygen Sensor or both. To be sure, however, an OBD2 scanner is recommended to diagnose what error codes may have been stored to determine which part requires attention.

Importantly too, both the MAF sensor and especially the O2 sensor are about the most ‘abused’ parts when it comes to replacements by the average Nigerian auto mechanic. While it is less visible with MAF sensors, O2 sensors, at least the OEMs would have the car make inscribed, but it is very common to have Toyota O2 sensors brought as replacement for a Nissan.

For many ‘rewires’ or auto mechanics, what matters is having it ‘read on a meter’, which only has to move without them understanding what it means, and it is certified good. The process of testing could be long, complicated and would be covered in a subsequent article.

Mounted in the air intake duct or air filter housing, a MAF sensor detects the air density as it heads into the engine intake to be mixed with fuel, noted autoguru.com.au. On the other hand, the oxygen sensor monitors how much unburned oxygen is present in the exhaust as exhaust exits the engine. The O2 sensor lets the computer know if the fuel mix is burning rich (not enough oxygen) or lean (too much oxygen). Knowing the ratio of fuel to air allows your vehicle’s engine to make any necessary changes to ensure that your car runs like it should, an article on cars.com notes.

Therefore, when one complains of excessive fuel consumption, these two are often singled out as suspects by the usual street mechanics that may not consider scanning important to ascertain what actually needs to be replaced. While the two in fact contribute to fuel consumption, they have other effects on vehicle performance that could make car usage either pleasurable or a nightmare.

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For rough idling or engine stalling for instance, the MAF sensor plays a role in this. From personal experience with a Nissan vehicle when it should be at about 600RPM in idle, it would drop and increase erratically as though the vehicle would go off. At times, after decelerating and coming to a stop, perhaps due to traffic or bad roads, the car could go off. Embarrassing to say the least but more so, an inconvenience that ensures the mind is not at ease while driving. There was also a wave of black smoke to herald the car’s arrival or departure.

As would always be recommended, a scan however failed to identify the MAF sensor as faulty. Taking a decision to replace this sensor was however done after two considerations; nothing in the scanner indicated a component responsible for the symptoms, even though signs were consistent with a faulty MAF sensor. More importantly, the MAF sensor inside the car at the time had been purchased from the Ladipo market.

The latter is most important as the process of buying parts like these at the famous Ladipo market would often entail inserting in the car, ensuring it starts, ‘behaves well’ for a few minutes of observation, and sent on its way.

However, sensors have part numbers, which must be strictly adhered to during replacements. An incompatible sensor would not always mean a vehicle would not start or ‘work well’, although there are instances when this would be the case. Even when a wrong sensor is used and appears to ‘work’ in the vehicle, performance is never optimal as its output has not been engineered for the engine it is being made to function.

Therefore, removing a MAF or O2 sensor from a Totoya Camry, would not necessarily mean it would work in a Toyota Corolla, simply because it fits in the other car, and both are Toyotas. The part numbers must be identical as the only manufacturer accepted way of replacing those parts.

Again, MAF and especially O2 sensors are perhaps the two most abused sensors when it comes to replacements, but these could also end up as costly errors when used in a vehicle that is very sensitive to the parts being used when they are not those designed for it by the manufacturer.

One way found to work was looking up the parts on Amazon, entering vehicle details with precision and then reviewing options marked as the right fit for such a car. It is a more expensive process that entails purchasing from Amazon, but when the used (tokunbo) is of absolute preference, the process could also be used to determine the appropriate part number to look out for when your mechanic is sent to the market.

The car manual also helps and should be consulted, as well as official websites of manufacturers, where one may be directed on getting the part number either on that part itself or casing around it. This could be dicey though, where the part being replaced had been previously changed with a wrong one.

When the Nissan that had the Ladipo MAF sensor was replaced with a proper (Hitachi) OEM fit, the stalling, rough idling, and wave of black smoke evaporated, and with that replacement some peace of mind was restored, at least for months now.

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