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Map Sensor Help!

Old 08-11-2005, 11:07 PM
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within the past week, i have 2 map sensors(gm 3 bar) that have failed. the first one was used for about 5000 miles, and all of a sudden stopped working, the pfc commander read +.22 reguardless of whether the car was being cranked or just off. i then replaced the MAP sensor with a new one and the car ran great for the next 200 miles, then all of a sudden in the highway, the car started choking again. now im stuck with a +.33 reading. i determined that the sensors are bad because whenever they are unplugged, i get a +2.17 reading.



i was not using a filter at the time, and was not aware that the nipple should have been facing down. with that said, and what my readings are saying. do you guys think that the diaphram is perforated? or could this be a wiring problem, maybe there is a crack in the harness that is shorting out and toasting the sensors?



any opinions would be appreciated.. thanks



martin





i have searched for how the map sensor works, and here is what i came up with.



he logic module uses the manifold absolute pressure (MAP) sensor to determine the absolute pressure (not the relative to atmospheric pressure) of the air inside the intake manifold and the atmosphere (barometric pressure).

This information is used to determine the density of the air entering the combustion chamber (in conjunction with the IAT(Intake Air temperature) sensor), which is used when calculating the proper air/fuel mixture for the engine, especially at WOT since the system is not in closed-loop at this time.

It is also used to help adjust the IAC(Idle Air Control) motor during idle.



It uses a silicon wafer that is thinner in the center (0.001") than around the edges (0.045"), which causes it to act as a diaphram.

It is mounted with a perfect vacuum beneath the chip so that the air pressure from the other side flexes the chip.

This flexing causes a change in resistance and the circuitry inside the sensor converts this to a voltage ranging from 0.02V to 4.94V when the output is pulled up towards 5V by the ECM(Electronic control module).



1 Bar MAP sensors are used on NA(naturally asperated) vehicles.

2 Bar MAP Sensors are used on forced induction vehicles(Turbo & Supercharged). They can measure up to 2x the apmospheric pressure(29.4psi), so that means it can measure up to 14.7psi boost(the atmosphere is 14.7psi + 14.7psi from the turbo/supercharger).

3 Bar MAP sensors can measure up to 44.1psi, which translates to 29.7psi boost from a Turbo/supercharger.



They all share a common pinout, although the connector keying may be different:

Pin A -- Ground

Pin B -- Sensor output

Pin C -- +5 volts

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Old 08-13-2005, 04:45 PM
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ive never seen a map sensor go bad, maybe it is just because its not facing down?
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