GM Full-Size Trucks 1988-1998 Repair Information

Upper Intake Manifold

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REMOVAL & INSTALLATION



4.3L Engines
1996-98 MODELS

The intake manifold assembly is a two-piece design. The upper portion is made from a composite material and the lower portion is cast-aluminum. The throttle body attaches to the upper manifold. The lower manifold has an Exhaust Gas Recirculation (EGR) port cast into the manifold for mixture of exhaust gases with the fuel and air mixture. The EGR valve bolts into the lower intake manifold.

The Central Sequential Multiport Fuel Injection (CSFI) system uses multiple injectors to meter and distribute fuel to each engine cylinder. The CSFI unit is retained by a bracket bolted to the lower intake manifold. The fuel meter body also houses the pressure regulator. Metal inlet and outlet fuel lines and nylon delivery tubes connect to the CSFI unit. The delivery tubes independently distribute fuel to each cylinder through nozzles located at the port entrance of each manifold runner where the fuel is atomized.


CAUTION
Fuel injection systems remain under pressure, even after the engine has been turned OFF. The fuel system pressure must be relieved before disconnecting any fuel lines. Failure to do so may result in fire and/or personal injury.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Remove the air cleaner box and intake duct.
  6.  
  7. Remove the wiring harness connectors and brackets and move them aside.
  8.  
  9. Disconnect the throttle linkage and bracket from the upper intake manifold.
  10.  
  11. Remove the cruise control cable (if equipped).
  12.  
  13. Remove the fuel lines and bracket at the rear of the lower intake manifold.
  14.  
  15. Remove the brake booster vacuum hose at the upper intake manifold.
  16.  
  17. Remove the PCV hose from the upper intake manifold.
  18.  
  19. Remove the ignition coil and bracket.
  20.  
  21. Remove the purge solenoid and bracket.
  22.  

Note the location of the manifold bolts and studs before removal for reassembly in their original positions.

  1. Remove the intake manifold bolts and studs.
  2.  

Do not disassemble the CSFI unit.

  1. Remove the upper intake manifold.
  2.  

To install:
  1. Install the upper intake manifold gasket.
  2.  
  3. Install the upper intake manifold.
  4.  

When installing the upper intake manifold be careful not to pinch the injector wires between the upper and lower intake manifolds.

  1. Install the upper intake manifold mounting bolts and studs in the same locations as prior to removal.
  2.  
  3. Tighten the bolts and studs in a crisscross pattern to 88 inch lbs. (10 Nm).
  4.  
  5. Install the purge solenoid and bracket.
  6.  
  7. Install the ignition coil and bracket.
  8.  
  9. Attach the PCV hose to the upper intake manifold.
  10.  
  11. Attach the fuel lines and bracket at the rear of the lower intake manifold.
  12.  
  13. Install the throttle linkage and bracket to the upper intake manifold.
  14.  
  15. Install the throttle linkage cable.
  16.  
  17. Install the cruise control cable (if equipped).
  18.  
  19. Install the wiring harness connectors and brackets.
  20.  
  21. Install the air cleaner box and intake duct.
  22.  
  23. Connect the negative battery cable.
  24.  
  25. Fill the cooling system.
  26.  
  27. Start the vehicle and verify no leaks.
  28.  

5.0 and 5.7L Engines
1996-98 MODELS

The 5.0L and 5.7L engines use a two-piece intake manifold design. The upper portion is made from a composite material and lower portion is cast-aluminum. The throttle body attaches to the upper manifold. The lower manifold has an Exhaust Gas Recirculation (EGR) port cast into the manifold for mixture of exhaust gases with the fuel and air mixture. The EGR valve bolts to the lower intake manifold.

The Central Sequential Multiport Fuel Injection (CSFI) system uses multiple injectors to meter and distribute fuel to each engine cylinder. The CSFI unit is retained by a bracket bolted to the lower intake manifold. The fuel meter body also houses the pressure regulator. Metal inlet and outlet fuel lines and nylon delivery tubes connect to the CSFI unit. The delivery tubes independently distribute fuel to each cylinder through nozzles located at the port entrance of each manifold runner where the fuel is atomized.

Note that the lower intake manifold gaskets are NOT reusable on the 5.0L and 5.7L engines.


CAUTION
Fuel injection systems remain under pressure, even after the engine has been turned OFF. The fuel system pressure must be relieved before disconnecting any fuel lines. Failure to do so may result in fire and/or personal injury.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner intake duct.
  4.  
  5. Remove the wiring harness connectors and brackets and move them aside.
  6.  
  7. Disconnect the throttle linkage and bracket from the upper intake manifold.
  8.  
  9. Remove the cruise control cable (if equipped).
  10.  
  11. Remove the PCV valve and hose.
  12.  
  13. Remove the fuel lines and bracket from the intake to the rear of the block.
  14.  
  15. Remove the ignition coil and bracket.
  16.  
  17. Remove the purge solenoid and bracket.
  18.  

Note the location of the manifold bolts and studs before removal for reassembly in their original positions.

  1. Remove the intake manifold bolts and studs.
  2.  

Do not disassemble the CSFI unit.

  1. Remove the upper intake manifold.
  2.  

To install:
  1. Install the upper intake manifold gasket.
  2.  
  3. Install the upper intake manifold.
  4.  

When installing the upper intake manifold be careful not to pinch the injector wires between the upper and lower intake manifolds.

  1. Install the upper intake manifold mounting bolts and studs in the same locations as prior to removal.
  2.  
  3. Tighten the bolts and studs in a crisscross pattern in 2 steps first to 45 inch lbs. (5 Nm) then to 83 inch lbs. (10 Nm).
  4.  
  5. Install the purge solenoid and bracket.
  6.  
  7. Install the ignition coil and bracket.
  8.  
  9. Attach the PCV hose to the upper intake manifold.
  10.  
  11. Attach the fuel lines and bracket at the rear of the block.
  12.  
  13. Install the cruise control cable (if equipped).
  14.  
  15. Install the throttle linkage and bracket to the upper intake manifold.
  16.  
  17. Install the throttle linkage cable.
  18.  
  19. Install the wiring harness connectors and brackets.
  20.  
  21. Install the air cleaner intake duct.
  22.  
  23. Connect the negative battery cable.
  24.  
  25. Start the vehicle and verify no leaks.
  26.  

7.4L Engines
1996-98 MODELS

See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: Upper intake manifold bolt tightening sequence-1996 7.4L engines

In 1996, the 7.4L engine was changed from Throttle Body Fuel Injection (TBI) to Sequential Fuel Injection (SFI). The intake manifold was changed to a two-piece unit. The upper half, often called a "plenum" mounts the throttle body assembly. The lower half of the intake manifold, which bolts to the cylinder heads, contains the fuel rail and injectors. Use care when working with light alloy parts. Work as clean as possible to prevent dirt and foreign material from entering the engine.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner intake duct.
  4.  
  5. Remove the wiring harness connectors and brackets and move them aside.
  6.  
  7. Remove the throttle and cruise control linkage (if equipped).
  8.  
  9. Remove the throttle body electrical connectors.
  10.  
  11. Remove the PCV valve and hose.
  12.  
  13. Remove the EGR inlet tube.
  14.  
  15. Remove the purge solenoid and connectors.
  16.  
  17. Remove the ignition coil and bracket.
  18.  
  19. Remove the No. 8 spark plug wire from the distributor.
  20.  
  21. Unfasten the upper intake manifold bolts and remove the upper intake manifold.
  22.  

To install:
  1. Clean all parts well. Clean all traces of gasket from the sealing surfaces.
  2.  
  3. Install a new upper intake manifold gasket.
  4.  
  5. Carefully place the upper intake manifold into position.
  6.  
  7. Install the upper intake manifold bolts and tighten them in sequence to 17 ft. lbs. (22 Nm) on 1996 models. On 1997-98 models tighten the bolts in two steps. On the first pass, tighten the bolts in sequence to 72 inch lbs. (8 Nm). On the second and final pass, tighten the bolts in sequence to 10 ft. lbs. (14 Nm).
  8.  
  9. Connect the No. 8 spark plug wire.
  10.  
  11. Install the ignition coil and bracket.
  12.  
  13. Install the purge canister and connectors.
  14.  
  15. Install the EGR inlet tube.
  16.  
  17. Install the PCV valve and hose.
  18.  
  19. Install the throttle body electrical connectors.
  20.  
  21. Install the throttle and cruise control linkage and bracket.
  22.  
  23. Install the wiring harness connectors and brackets.
  24.  
  25. Install the air cleaner intake duct.
  26.  



Click image to see an enlarged view

Fig. Fig. 2: Upper intake manifold bolt tightening sequence-1997-98 7.4L engines

 
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