The MAP (manifold absolute pressure) sensor relays turbocharger boost pressure to the PCM. This, in conjunction with other information, is used to determine engine fueling characteristics. When a MAP sensor fails or returns faulty values, the PCM resorts to a default value, often limiting performance and reducing fuel economy. It is also common for the vacuum line that supplies pressure to the MAP sensor to crack, deteriorate, and ultimately leak. Since vacuum line is vastly cheaper than the sensor itself, we'd recommend replacing the supply line first and seeing if that relieves the problem before purchasing a new sensor.
How to Replace the MAP Sensor on a 7.3 Power Stroke Diesel
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• The map sensor is located against the passenger side firewall (red arrow in image to the left).
• Disconnect both negative battery cables.
• To remove the electrical connector from the bottom of the MAP sensor, first slide the red clip downwards to expose the release button, then press the release button while pulling the connector downwards.
• A 1/4" vacuum line runs from the sensor to the intake manifold. It is held on by two quick release clips - use a pair of pliers to release the clip and slide it over the nipple so that the line can be removed. If you are replacing the MAP sensor, it is wise to replace the line as well, which has a tendency to crack over time.
• Installation of the new sensor is reverse.