Air Measurement System

WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 2011 Mercury Mariner, 2011 Lincoln Navigator L, 2011 Lincoln Navigator, 2011 Lincoln MKX, and 2011 Lincoln MKT. However, it is still accessible from the selected car via links, so may be relevant.

With this condition, the engine runs rich or lean of stoichiometry (14.7:1 air/fuel ratio) if the powertrain control module (PCM) is not able to compensate enough to correct for the condition. One possibility is the mass of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. For example, with a contaminated MAF sensor, the engine runs lean at higher RPM because the PCM delivers fuel for less air than is actually entering the engine. Example:

The MAF sensor measurement is inaccurate due to a corroded connector, contaminated or dirty connector. A contaminated MAF sensor typically results in a rich system at low airflows (PCM reduces fuel) and a lean system at high airflows (PCM increases fuel).

With this condition, the engine runs rich or lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. One possibility, the MAF sensor measurement is inaccurate due to a corroded connector, contamination or dirt on the MAF sensor screen or element. A contaminated MAF sensor typically results in a rich system at low airflows (PCM reduces fuel) and a lean system at high airflows (PCM increases fuel).