HFM Mass Airflow Sensor, Bremi - E36 325i/M3, E34 525i/530i, M50, S50US

This part is listed by BMW as BMW part number 13621747155 (13 62 1 747 155) and is described as Bremi HFM (Mass Air Sensor) for 1992-1995 E36 325i/M3, 1991-1995 E34 525i, and 1993-1995 E34 530i. It can also be used on any other M50/M52/S50/S52 that has been fully converted to OBD1 wiring harness and electronics (such as an engine swap).

This is the stock-sized HFM used for the above cars. Upgrades may also be available, depending on model.

The HFM (Hot Film Meter, or MAF) measures air density and temperature in the intake so the engine computer can make fuel adjustments on the fly. When it goes bad and no longer sends data the ECU will revert to a rich setting (more fuel) and eventually it will throw a fault code. If you're having drivability issues or MPG has dropped, remove the HFM and intake boots, clean with HFM cleaner, check for cracks in the boots, and reinstall. If problems persist it may be time for a new HFM.

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