GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

CMFI Assembly

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REMOVAL & INSTALLATION



See Figures 1 and 2

The CMFI assembly is mounted to the lower intake manifold. The upper intake manifold assembly must be removed for access. The CMFI assembly includes a fuel meter body, gasket seal, fuel pressure regulator, fuel injector and six poppet nozzles with fuel tubes. Should a failure occur in any components of the CMFI unit, the entire assembly must be replaced.

  1. Remove the plastic cover and properly relieve the fuel system pressure.
  2.  
  3. Disconnect the negative battery cable, then remove the air cleaner and air inlet duct.
  4.  
  5. Unplug the wiring harness from the necessary upper intake components including:

    Throttle Position (TP) sensor
     
    Idle Air Control (IAC) motor
     
    Manifold Absolute Pressure (MAP) sensor
     
    Intake Manifold Tuning Valve (IMTV)
     

  6.  
  7. Disconnect the throttle linkage from the upper intake manifold, then remove the ignition coil.
  8.  
  9. Disconnect the PCV hose at the rear of the upper intake manifold, then tag and unplug the vacuum hoses from both the front and rear of the upper intake.
  10.  
  11. Remove the upper intake manifold bolts and studs, making sure to note or mark the location of all studs to assure proper installation. Remove the upper intake manifold from the engine.
  12.  



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the upper and lower intake manifolds and the CMFI system components

  1. Unplug the injector wiring harness connector at the CMFI assembly.
  2.  
  3. Remove and discard the fuel fitting clip.
  4.  
  5. Disconnect the fuel inlet and return tube and fitting assembly. Discard the old O-rings.
  6.  
  7. Squeeze the poppet nozzle locktabs together while lifting each nozzle out of the casting socket. Once all six nozzles are released, carefully lift the CMFI assembly out of the casting.
  8.  

To install:
  1. Align the CMFI assembly grommet with the casting grommet slots and push downward until it is seated in the bottom guide hole.
  2.  


CAUTION
To reduce the risk of fire and personal injury, be ABSOLUTELY SURE that the poppet nozzles are firmly seated and locked into their casting sockets. An unlocked poppet nozzle could work loose from its socket resulting in a dangerous fuel leak.

  1. Carefully insert the poppet nozzles into the casting sockets. Make sure they are FIRMLY SEATED and locked into the casting sockets.
  2.  
  3. Position new O-ring seals (lightly coated with clean engine oil), then connect the fuel inlet and return tube and fitting assembly.
  4.  
  5. Install a new fuel fitting clip.
  6.  
  7. Temporarily connect the negative battery cable, then pressurize the fuel system by cycling the ignition switch ON for 2 seconds, then OFF for 10 seconds and repeating, as necessary. Once the fuel system is pressurized, check for leaks.
  8.  
  9. Disconnect the negative battery cable.
  10.  



Click image to see an enlarged view

Fig. Fig. 2: Upper intake manifold torque sequence

  1. Position a new upper intake manifold gasket on the engine, making sure the green sealing lines are facing upward.
  2.  
  3. Install the upper intake manifold being careful not to pinch the fuel injector wires between the manifolds.
  4.  
  5. Install the manifold retainers, making sure the studs are properly positioned, then tighten them using the proper sequence to specifications. Refer to Engine and Engine Rebuilding of this repair guide for the manifold specification.
  6.  
  7. Connect the PCV hose to the rear of the upper intake manifold and the vacuum hoses to both the front and rear of the manifold assembly.
  8.  
  9. Connect the throttle linkage to the upper intake, then install the ignition coil.
  10.  
  11. Attach the necessary wiring to the upper intake components including the TP sensor, IAC motor, MAP sensor and the IMTV.
  12.  
  13. Install the plastic cover, the air cleaner and air inlet duct.
  14.  
  15. Connect the negative battery cable.
  16.  

 
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