On a 2001 Ford E-150 van, the Mass Air Flow (MAF) sensor is typically located in the intake tubing,
between the air filter housing and the throttle body. It's usually a relatively small, rectangular or cylindrical sensor with a wire harness connected to it. You'll likely find it within a few inches of the air filter box, on the path of air flowing into the engine.
However, the exact location can vary slightly depending on the engine type (4.2L, 4.6L, 5.4L, etc.) and specific van configuration. A visual inspection, consulting a repair manual specific to your van's engine, or using an online parts diagram specific to your VIN are your best bets for precise location.
