The internal workings of a car engine are complex and precise, but if all is well mechanically, a gasoline engine needs three things to run: air, fuel, and spark. Air and fuel need to be metered out in an exact ratio for optimal performance. So when one increases or decreases, the computer (ECU) endeavors to maintain the perfect mixture. To do this, it needs to read measurements about how much air is going into the engine at any given time. This is when having a bad Mass Air Flow sensor (MAF) becomes a problem.
Check My Flow
A MAF sensor is usually placed in-line immediately after the air filter, and takes a reading of how much air is entering the engine. It takes account of the air flow and converts it to an electrical signal sent to the ECU. The ECU sees this reading and adjusts the fuel volume that passes through the injectors. Too much fuel gives you a “rich” mixture, and there will be some left over after the combustion. Not only does this affect your fuel economy, but it can create untimed detonations or “knocking,” and can leave a nasty buildup of particles in the combustion chamber, mucking up your spark plugs in the process. A “lean” mixture is too much air. This can create misfires, rough idles, and may make the engine difficult to start at all. So it’s important to get proper readings from the MAF so that the ECU can do its job maintaining the correct ratio.
Go With the Flow
When the MAF sensor isn’t working, you’ll know it. First off, your air-fuel ratio will be wrong, so you’ll have a case of lean or rich mixtures. So your fuel economy will fall, and your performance will suffer. A check engine light may yield a code about lean or rich mixtures, but it won’t pinpoint the MAF sensor itself. You or a qualified mechanic will have to troubleshoot whether it is the MAF sensor, the electrical circuit, the ECU, or another component entirely that is causing the problem. Once you ensure it is, in fact, the sensor, it’s time for a change.
MAF sensors can become damaged, but more often they just get too dirty to do their job well. In this case, they can be cleaned but if it is a mechanical or electrical failure, they must be replaced. Luckily, it’s a pretty straightforward job. Since it’s right next to the air filter, they’re usually very accessible without having to remove too much (if anything) to get to them. Oftentimes, it’s as easy as disconnecting a clamp, a few bolts and the electrical connector. Make sure to keep the new one clean, and pay close attention when installing it to ensure that it’s facing the correct way. Oftentimes the flow is indicated with an arrow, but otherwise, the included instructions should tell you. And that’s it! Just swap ’em out and your engine performance should improve.
MAF sensors give valuable information to engines with electronic fuel injected systems, so you don’t want to delay in getting it fixed if yours is acting up. And considering how easy it is, there’s really no excuse not to.
For an example of a typical repair, here’s how to replace a MAF sensor on a 2003 Ford Escape 3.0L V6 engine:
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Photos courtesy of Blair Lampe.
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.