Ram B1500, B2500, B3500, 1999-2003

Manifold Absolute Pressure Sensor

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Operation



The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, by measuring the vacuum level. It sends a voltage signal to the ECM in relation to the pressure inside the manifold, which varies according to engine load and altitude. The ECM uses this signal to adjust the air/fuel ratio.

The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, by measuring the vacuum level. It sends a voltage signal to the ECM in relation to the pressure inside the manifold, which varies according to engine load and altitude. The ECM uses this signal to adjust the air/fuel ratio.

The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, by measuring the vacuum level. It sends a voltage signal to the PCM in relation to the pressure inside the manifold, which varies according to engine load and altitude. The PCM uses this signal to adjust the air/fuel ratio (injector pulse width) and spark advance.

A 5-volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero-pressure reading is 0.5 volt and full scale is 4.5 volts. For a pressure swing of 0-15 psi, the voltage changes 4.0 volts. To operate the sensor, it is supplied a regulated 4.8-5.1 volts. Ground is provided through the low-noise, sensor return circuit at the PCM.

MAP sensor input is the primary contributor to fuel injector pulse width. The most important function of this sensor is to determine barometric pressure. The PCM needs to know if the vehicle is at sea level or high altitude because air density changes with altitude. As altitude goes up, barometric pressure goes down.

Readings are taken every 12 msec.

The PCM uses the MAP sensor input to aid in calculating the following parameters:



Manifold pressure
 
Barometric pressure
 
Engine load
 
Injector pulse width
 
Spark advance
 
Shift-point strategies
 
Idle speed
 
Decel fuel shutoff
 



Click image to see an enlarged view

Fig. MAP sensor location-8.0L engine

Removal & Installation



2.5L, 3.9L, 5.2L, 5.9L Engines
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Remove the two MAP sensor retaining bolts.
  6.  
  7. Slide the L-shaped tube to the MAP sensor from the throttle body off while removing the MAP sensor from the throttle body.
  8.  

To install:

  1. Install the L-shaped tube onto the MAP sensor.
  2.  
  3. Position the sensor to the throttle body while guiding the rubber fitting over the throttle body vacuum nipple.
  4.  
  5. Install the MAP sensor onto the throttle body assembly. Tighten the retaining bolts to 25 inch lbs. (3Nm). If applicable, install the throttle body.
  6.  
  7. Install the air cleaner assembly.
  8.  
  9. Connect the negative battery cable.
  10.  



Click image to see an enlarged view

Fig. MAP mounting screws-typical

4.7L
  1. Clean the area around the sensor before removal to keep debris out of the intake tract.
  2.  
  3. Remove the electrical connector.
  4.  
  5. Remove the sensor mounting bolts, and then remove the sensor.
  6.  

To install:

  1. Make sure the sensor seal is in good condition.
  2.  
  3. Clean the sensor and lubricate the rubber gasket with clean engine oil.
  4.  
  5. Clean the sensor opening in the intake manifold.
  6.  
  7. Install the sensor, tighten the bolts to 20 inch lbs. (2 Nm).
  8.  
  9. Connect the wires to the sensor.
  10.  

Testing




WARNING
Testing the wiring harness with the ECM still connected can cause serious damage to the processor. ALWAYS disconnect the ECM before testing the wiring harness, unless instructed otherwise.

  1. Remove the engine cover.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Inspect the L-shaped tube from the throttle body to the MAP for cracks, blockage, and damage. Repair as necessary.
  6.  
  7. Unplug the MAP sensor connector.
  8.  
  9. Test the MAP sensor output voltage at the MAP sensor connector between terminals A and B. With ignition
  10.  
  11. ON and the engine OFF, the voltage should be between 4-5 volts. If no voltage is present, proceed to Step 8.
  12.  
  13. Test MAP sensor supply voltage at sensor connector between terminals A and C with the ignition ON and engine off, voltage should be 4.5-5.0 volts. If no voltage is present, proceed to Step 8.
  14.  
  15. Test the MAP sensor ground circuit at terminal A of the MAP connector; voltage should be less than 0.2 volts. If not inspect for open harness from pin 4 of ECM harness and terminal A. If no voltage is present, proceed to the next step.
  16.  
  17. Turn the ignition OFF.
  18.  
  19. Disconnect the ECM harness from the ECM.
  20.  
  21. Test the MAP sensor output voltage at the ECM connector. At the ECM harness connector test pin 1 of the connector, the voltage should be the same as at the MAP sensor in Step 5.
  22.  
  23. Check ECM harness connector pin 6 for the same voltage as in Step 6.
  24.  
  25. If all of the above tests pass, plug in ECM wiring harness and MAP sensor connector.
  26.  
  27. With the ignition in the ON position, and the engine OFF, remove the tube from the throttle body to the MAP sensor.
  28.  
  29. Connect a vacuum pump to the nipple on the MAP sensor, and pump the sensor to 20-27 in. Hg. of vacuum. Check the sensor output voltage, it should be below 1.8 volts. If not, replace the MAP sensor. If the voltage is OK, proceed to next step.
  30.  
  31. Relieve vacuum pressure on the sensor, and then check the output voltage. The voltage should be 4-5 volts; if not, replace the MAP sensor.
  32.  
  33. Install the air cleaner assembly.
  34.  
  35. Install the engine cover.

    Click image to see an enlarged view

    Fig.



    Click image to see an enlarged view

    Fig.

  36.  


WARNING
Testing the wiring harness with the ECM still connected can cause serious damage to the processor. ALWAYS disconnect the ECM before testing the wiring harness, unless instructed otherwise.

  1. Remove the engine cover.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Inspect the L-shaped tube from the throttle body to the MAP for cracks, blockage, and damage. Repair as necessary.
  6.  
  7. Unplug the MAP sensor connector.
  8.  
  9. Test the MAP sensor output voltage at the MAP sensor connector between terminals A and B. With ignition
  10.  
  11. ON and the engine OFF, the voltage should be between 4-5 volts. If no voltage is present, proceed to Step 8.
  12.  
  13. Test MAP sensor supply voltage at sensor connector between terminals A and C with the ignition ON and engine off, voltage should be 4.5-5.0 volts. If no voltage is present, proceed to Step 8.
  14.  
  15. Test the MAP sensor ground circuit at terminal A of the MAP connector; voltage should be less than 0.2 volts. If not inspect for open harness from pin 4 of ECM harness and terminal A. If no voltage is present, proceed to the next step.
  16.  
  17. Turn the ignition OFF.
  18.  
  19. Disconnect the ECM harness from the ECM.
  20.  
  21. Test the MAP sensor output voltage at the ECM connector. At the ECM harness connector test pin 1 of the connector, the voltage should be the same as at the MAP sensor in Step 5.
  22.  
  23. Check ECM harness connector pin 6 for the same voltage as in Step 6.
  24.  
  25. If all of the above tests pass, plug in ECM wiring harness and MAP sensor connector.
  26.  
  27. With the ignition in the ON position, and the engine OFF, remove the tube from the throttle body to the MAP sensor.
  28.  
  29. Connect a vacuum pump to the nipple on the MAP sensor, and pump the sensor to 20-27 in. Hg. of vacuum. Check the sensor output voltage, it should be below 1.8 volts. If not, replace the MAP sensor. If the voltage is OK, proceed to next step.
  30.  
  31. Relieve vacuum pressure on the sensor, and then check the output voltage. The voltage should be 4-5 volts; if not, replace the MAP sensor.
  32.  
  33. Install the air cleaner assembly.
  34.  
  35. Install the engine cover.

    Click image to see an enlarged view

    Fig.



    Click image to see an enlarged view

    Fig.

  36.  

The MAP sensor is fitted to the front of the throttle body except on 4.7L and 8.0L engines where it is installed on the intake manifold.

  1. Remove the air cleaner assembly.
  2.  
  3. On throttle-body mounted MAP sensors, inspect the L-shaped tube from the throttle body to the MAP for cracks, blockage, and damage. Repair as necessary.
  4.  
  5. Unplug the MAP sensor connector.
  6.  
  7. Test the MAP sensor output voltage at the MAP sensor connector between terminals "sensor ground" and "sensor signal". With ignition ON and the engine OFF , the voltage should be between 4-5 volts.
  8.  
  9. Check voltage across the same terminals with the engine running at idle at operating temperature. Voltage should be 1.5-2.1 volts.
  10.  
  11. Test MAP sensor supply voltage at sensor connector between terminals "sensor ground" and "5v supply" with the ignition ON and engine off, voltage should be 4.5-5.0 volts.
  12.  
  13. Test the MAP sensor ground circuit at the "sensor ground" of the MAP connector, voltage should be less than 0.2 volts. If not inspect for open harness from pin 4 of PCM harness and terminal A . If no voltage is present, proceed to the next step.
  14.  
  15. Turn the ignition OFF .
  16.  
  17. Disconnect the PCM harness from the PCM.
  18.  


WARNING
Testing the wiring harness with the PCM still connected can cause serious damage to the processor. ALWAYS disconnect the PCM before testing the wiring harness, unless instructed otherwise.

  1. Test the MAP sensor output voltage at the PCM connector. At the PCM cavity A-27 , the voltage should be about 5.0 volts.
  2.  
  3. Check the voltage at PCM cavity A-17 . It should be 5.0 volts.
  4.  
  5. If all of the above tests pass, plug in PCM wiring harness and MAP sensor connector.
  6.  
  7. With the ignition in the ON position, and the engine OFF , remove the tube from the throttle body to the MAP sensor.
  8.  
  9. Connect a vacuum pump to the nipple on the MAP sensor, and pump the sensor to 20-27 in. Hg. Check the sensor output voltage, it should be below 1.8 volts. If not, replace the MAP sensor. If the voltage is OK, proceed to next step.
  10.  
  11. Relieve vacuum pressure on the sensor, then check the output voltage. The voltage should be 4-5 volts; if not, replace the MAP sensor.
  12.  
  13. Install the air cleaner assembly.
  14.  



Click image to see an enlarged view

Fig. MAP sensor electrical connector-except 4.7L and 8.0L engines. Wire colors are (1) BK/LB (sensor ground), (2) DG/RD (sensor signal), and (3) ORN (5-volt supply)



Click image to see an enlarged view

Fig. Testing the MAP sensor



Click image to see an enlarged view

Fig. MAP sensor connector-8.0L engine



Click image to see an enlarged view

Fig. MAP sensor connector-4.7L engine. (1) ORN (5-volt supply), (2) BK/LB (sensor ground), and (3) DG/RD (sensor signal)

 
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