Roadmaster 1992

Manifold Absolute Pressure Sensor

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Location





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Fig. MAP sensor location-1991-1993

Operation



The Manifold Absolute Pressure (MAP) Sensor is a piezoelectric (pressure-sensitive) electronic device that monitors the intake manifold vacuum and atmospheric pressure. The MAP Sensor operates within a 5 volt DC reference range, and provides a linear input signal to the Powertrain Control Module (PCM) that is based upon a comparison of air density and intake manifold vacuum under measured operating conditions. The PCM uses data from the MAP Sensor to calculate air-fuel mixture, ignition timing, and fuel injector pulse width.

Removal & Installation



  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    Disconnecting the negative battery cable on some vehicles may interfere with the functions of the on-board computer systems and may require the computer to undergo a relearning process, once the negative battery cable is reconnected.


    NOTE
    If working near and/or around the SRS system and components, be sure to properly disable the SRS system. See disarming/arming the SRS system.

  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Disconnect the vacuum harness assembly.
  6.  
  7. Release the electrical connector.
  8.  
  9. Remove the bolts or release the MAP sensor locking tabs and remove the sensor.

    Click image to see an enlarged view

    Fig. MAP sensor and related components-1991-1993

  10.  

To install:


NOTE
Be sure to use new fasteners, as required.


NOTE
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread sealer are identified. Do not use paints, lubricants or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners.

  1. Install the bolts or snap sensor onto the bracket.
  2.  
  3. Connect the MAP sensor electrical connector.
  4.  
  5. Connect the MAP sensor vacuum harness connector.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Using the GM diagnostic scan tool or aftermarket equivalent reprogram the necessary systems and components. Be sure to follow the scan tool manufacturer-s directions.
  10.  

Testing




NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Connection & Wiring Diagnosis

Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.  

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

MAP Circuit Testing

Use a suitable scan tool, a Graphing Multi-Meter (GMM), or a Digital Volt-Ohm Meter (DVOM) in order to view the MAP data.

MAP Sensor logic is relative to the scale of resistance: when the manifold absolute pressure is low, the voltage is decreased. When the coolant temperature is high, the voltage is increased.

Inspect the air intake tube, the engine air filter, and the MAP sensor for contamination and physical damage in order to verify that the air induction system is in proper working order. If an air induction system fault is evident, repair as required before continuing.

If a DVOM is being used, additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If a significant voltage drop is measured (greater than 0.5 volts DC), check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the MAP Sensor to verify the signal with a DVOM, and verify PCM communication before replacing the MAP Sensor.

Click image to see an enlarged view

Fig. MAP Sensor Range Chart

MAP Sensor Strategy

The MAP Sensor provides a linear input signal to the Powertrain Control Module (PCM) for a number of engine control system calculations. The MAP signal is compared with Mass Air Flow (MAF), Intake Air Temperature (IAT), and Fuel Trim (HO2S) in order to determine the correct air-fuel mixture for measured operating conditions.

Related Diagnostic Trouble Codes


Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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