Map sensor problems
Map sensor problems are more common on certain models. As far as engine computer sensor reliability this is one of the sensors that appear to be more reliable overall. But on a few models poor mounting location chosen by the factory may reduce its reliability. For example on the Chevrolet diesel engine that is found in many 3500 series pickup trucks and work vans the map sensor is mounted directly to the intake manifold. The engine sensor pictured to the right is from a 6.5 liter diesel. The orange ring is what actually seals the vacuum input signal port to the intake manifold.
With the map sensor being made out of plastic and mounted directly to an intake manifold that generates a lot of heat it is not uncommon to find a problem with the map sensor on this configuration. On most GM models it is mounted on a bracket and a vacuum line provides the input signal. On the Chevrolet turbo diesel engine it is sometimes called a boost sensor and fits into a small hole directly drilled into the intake manifold.
Information about pressure sensors
The word m.a.p. stands for manifold absolute pressure. This engine sensor measures changes in the intake manifold pressure that can result from changes in the engine load and speed. Not to get overly scientific but it measures the difference between barometric pressure and the actual manifold pressure. An example would be a wide open throttle position will produce a high value because the pressure in the manifold is approaching the same pressure as outside the manifold. This is sometimes known as an inverse measurement because it is opposite of what you would see on a vacuum gauge. The advantage of comparing the manifold pressure with barometric pressure is this will allow the engine to properly meter air fuel mixture regardless of the altitude that the vehicle is operating at. As an example a vehicle that operates in Colorado would require a much different air fuel mixture than a vehicle operating below sea level in New Orleans.
Diagnosing engine senor problemsI have also seen disconnected and or damaged vacuum lines that can cause problems as well. Both of these common problems can be detected with a good visual inspection.
The map sensor allows for automatic compensation and proper air fuel mixture regardless of altitude. This also relies on the outside air temperature that can change the airs density that is entering the engine. The information supplied to the computer from the air temperature sensor helps it perform adjustments on the fly. It is very rare but with some map sensor problems that I have diagnosed it was actually the air temperature sensor that was causing the problem. This is one of the reasons that I recommend a vehicle specific auto repair manual and to follow the steps outlined in the diagnostic tree chart for the set code. It also helps if you select an online version that provides technical service bulletins that may identify any common problems associated with that particular vehicle such as the Chevrolet diesel engine mentioned above. Give this Diy car repair page a  Custom Search The you fix cars homepage is a good place to review what other kinds of information is available here for Diy car mechanics. You can also find out how to get your car repair questions answered.
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In the case of a 3500 series work van the engine has a tendency to build up more heat. This is because of an engine cover that is common on most vans.
