Mass Air Sensors

David S.
By David S. Wallens
Jul 10, 2001 | BMW | Posted in Electronics & Electrical Systems | Never miss an article

Vane-type air flow meters are simple and effective, yet they are often seen as a bottleneck when trying to increase performance. Tuners say they block the incoming air, while they their lack of adjustment can be a problem on a modified engine.

Eager to see what kind of gains could be made, we converted two cars from air flow meters to more modern setups—our Miata project received the Flyin’ Miata/Link Programmable ECU while we went with Split Second’s MAF kit on our E30-chassis BMW M3. Both systems were basically plug-in-and-play setups for the respective car. As a bonus, both systems allow additional tuning.

Both installations were done at Atlanta’s Engineered Performance under the eye of dyno tuner Ed Senf. Watching Ed tune both systems made us realize how a knowledgeable dyno tuner can make or break a project. Additionally, Rennie Bryant from Redline BMW Performance helped with the M3 conversion.

All 1.6-liter Miatas (1990-‘93 production) use an air flow meter, which the Flyin’ Miata/Link Programmable ECU replaces with a manifold absolute pressure sensor (MAP). Where the air flow meter uses a hinged air vane to determine the amount of incoming air, the MAP monitors the amount of manifold air pressure and converts that figure into a voltage signal. This signal is sent to the car’s computer to determine the proper amount of fuel and ignition.

The Flyin’ Miata/Link Programmable ECU replaces the stock ECU board, while the supplied MAP sensor plugs into the stock wiring harness. The system has an “auto tune” feature, although further tuning was done at Engineered Performance on their Dynojet chassis dyno. The Flyin’ Miata/Link Programmable ECU allows full control over fuel curves, timing curves, rev limit and so on.

In addition to the parts included with the Flyin’ Miata/Link Programmable ECU (ECU board, keypad, MAP sensor and instructions), we also added a Flyin’ Miata knock sensor, four-wire oxygen sensor and Injector Air Fuel Ratio Monitor from Racer Wholesale Parts.

And now for the M3

Our 1988 BMW M3 received a slightly different conversion, as it lost its air flow meter and gained a mass air flow sensor. A mass air flow sensor (MAF) uses a heated wire to measure the amount of incoming air. The more electricity needed to keep the wire at the desired temperature, the more air that is going into the engine. This information is sent to the car's computer, which determines the necessary amount of fuel and spark needed at the moment.

The Split Second MAF kit for the M3 includes the mass air flow sensor, wiring harness, air intake tube, ARM1 air-fuel ratio meter and ARC2 Air/Fuel Ratio Calibrator, a four-channel control box regulates low, mid, high and acceleration levels, working with the stock BMW computer.

We'll cover all of the details in the December issue of GRM, but we won't keep you in suspense forever: Both systems helped us make more power, and neither one was particularly hard to install. We would say tuning them on a chassis dyno is a requirement, however. Adjusting knobs or punching buttons while driving down the street at wide open throttle isn't exactly safe.

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