GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Intake Manifold

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REMOVAL AND INSTALLATION



3.1L Engine

The intake manifold is a one-piece cast aluminum unit. It centrally supports a TBI unit.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Remove the rocker arm covers, as outlined in this section.
  6.  
  7. Remove the TBI unit, as follows:
    1. Relieve the fuel system pressure, as outlined in Fuel System .
    2.  
    3. Remove the air cleaner assembly.
    4.  
    5. Tag and detach the electrical connectors from the IAC motor, TP sensor and the fuel injectors.
    6.  
    7. Remove the injector wiring harness.
    8.  
    9. Disconnect the throttle cable, transmission control cable, and cruise control cable (where applicable).
    10.  
    11. Unfasten the cable support bracket attaching screws, then remove the bracket.
    12.  
    13. Tag and disconnect the vacuum hoses that interfere with the TBI assembly, and set them aside.
    14.  
    15. Using a back-up wrench on the line nuts, remove the fuel feed and return lines. Pull the fuel line O-rings off and discard them, after matching them up with new ones.
    16.  
    17. Unfasten the TBI attaching nuts/bolts, then remove the TBI unit and flange gasket.
    18.  

  8.  
  9. Unbolt the power steering pump and lay it aside. Do not disconnect the fluid lines.
  10.  
  11. Remove the distributor, as outlined in Engine Electrical of this repair guide.
  12.  
  13. Remove the retaining nuts and bolts, then lift off the intake manifold. Place a clean shop towel in the lifter valley to catch any gasket material.
  14.  
  15. Thoroughly clean the gasket material from the sealing surfaces, and the old RTV from the ridges. Wipe the sealing surfaces clean with degreaser. REMOVE THE SHOP TOWEL from the lifter valley.
  16.  

See Figure 1

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Fig. Fig. 1: Exploded view of the intake manifold, including the tightening sequence-3.1L engine

To install:
  1. Apply a 3 / 16 in. (5 mm) bead of RTV sealer on each ridge. Install a new intake gasket.
  2.  
  3. Apply sealer to the threads of the intake manifold retaining studs.
  4.  
  5. Carefully seat the intake manifold without disturbing the intake gaskets, and to get the best seal from the RTV.
  6.  
  7. Install the intake manifold retainers. Refer to the accompanying diagram for the tightening sequence and specifications.
  8.  
  9. Install the rocker arm covers, as outlined in this section.
  10.  
  11. Position the TBI unit flange gasket, then install the TBI unit and tighten the bolts/nuts to 18 ft. lbs. (25 Nm).
  12.  
  13. Install new O-rings on the fuel lines, then connect the lines. Use a backup wrench to tighten the nuts to 20 ft. lbs. (27 Nm).
  14.  
  15. Tighten the cable support bracket attaching screws and reconnect the throttle cable, transmission control cable, and cruise control cable (where applicable). Make sure the throttle and cruise control cables do not hold the throttle open.
  16.  
  17. Attach the injector wiring harness and the electrical connectors, as tagged during removal. Make sure the connectors are fully seated and their latches locked, if applicable.
  18.  
  19. Connect the negative battery cable. Cycle the ignition key ON and OFF (do not start the engine) a couple of times and check for fuel leaks.
  20.  
  21. With the engine OFF , depress the pedal to the floor and release, to check to see that the accelerator pedal is free.
  22.  
  23. Install the air cleaner assembly.
  24.  
  25. Reset the IAC valve pintle position as follows:
    1. Depress the accelerator pedal slightly.
    2.  
    3. Start and run the engine for three seconds-turn ignition off for ten seconds.
    4.  
    5. Restart engine and check for proper idle operation.
    6.  

  26.  

3.4L Engine

This engine uses a sequential multiport fuel injection system. During installation, you must attach the injector electrical connectors to their appropriate fuel injector, or exhaust emissions and engine performance may be seriously affected.

UPPER MANIFOLD
  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Properly relieve the fuel system pressure, as outlined in Fuel System .
  6.  
  7. Remove the fuel injector sight shield.
  8.  
  9. Remove the air cleaner duct.
  10.  
  11. Remove the accelerator control and cruise control cables, with the bracket, from the throttle body.
  12.  
  13. Tag and detach the wiring harness connectors from the throttle body. Lay the harness aside.
  14.  
  15. Remove the thermostat bypass pipe coolant hoses from the throttle body.
  16.  
  17. Label the vacuum lines and disconnect them from the connections at the throttle body.
  18.  
  19. Tag and disconnect the left side (front) spark plug wires, and set them aside.
  20.  
  21. Remove the ignition coil bracket with the coils, the purge solenoid and the vacuum canister solenoid.
  22.  
  23. Remove the Manifold Absolute Pressure (MAP) sensor and bracket.
  24.  

See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the upper intake manifold assembly-3.4L engine

  1. Tag and disconnect the vacuum hose connections from the upper intake manifold.
  2.  
  3. Remove the rear alternator brace.
  4.  
  5. Remove the Exhaust Gas Recirculation (EGR) valve.
  6.  
  7. Unfasten the upper intake manifold nuts and bolts, then remove the upper intake manifold.
  8.  
  9. Remove the upper intake gasket, be careful not to mar or scratch the sealing surfaces while cleaning them with degreaser.
  10.  

On some applications, you may want to remove the throttle body.

  1. Installation is the reverse of the removal procedure. Make sure to tighten all retainers evenly and securely. Attach all electrical connections and vacuum lines as tagged during removal. Fill all fluids to their proper levels, and check for leaks.
  2.  

LOWER MANIFOLD
  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Properly relieve the fuel system pressure, as outlined in Fuel System of this repair guide..
  6.  
  7. Remove the upper intake manifold, as outlined in this section.
  8.  
  9. Remove the left (front) and right (rear) rocker arm covers. Refer to the procedure given in this section.
  10.  
  11. Use a backup wrench to disconnect the fuel feed and return pipe from the fuel injector rail.
  12.  
  13. Remove the fuel rail assembly. For more details, refer to Fuel System of this repair guide.
  14.  
  15. Unbolt the power steering pump from the front engine cover and reposition it to one side. Do not disconnect the fluid lines.
  16.  
  17. Disconnect the heater inlet pipe from the lower intake manifold and the upper radiator hose from the engine.
  18.  
  19. Unfasten the lower intake manifold bolts, then lift the lower intake manifold off of the engine.
  20.  
  21. Remove the lower intake manifold gasket and the RTV sealer. Thoroughly clean the gasket mating surfaces with a suitable degreaser.
  22.  

See Figure 3

Click image to see an enlarged view

Fig. Fig. 3: Lower intake manifold

To install:
  1. Apply a bead of RTV sealer on each ridge where front and rear of the lower intake manifold contact the engine block. Install the lower intake manifold gaskets.
  2.  


WARNING
An oil leak may result if the vertical attaching bolts are not tightened before the diagonal attaching bolts.

  1. Position the lower intake manifold onto the block. Align the bolt holes. Apply sealer to the manifold bolts and install hand tight into the manifold. Tighten the vertical attaching bolts first, to 115 inch lbs. (13 Nm), then the diagonal bolts to 115 inch lbs. (13 Nm).
  2.  
  3. Connect the upper radiator hose to the engine .
  4.  
  5. Connect the heater inlet pipe to the lower intake manifold.
  6.  
  7. Install the power steering pump to the front engine cover.
  8.  
  9. Install the fuel rail, as outlined in Fuel System of this repair guide.
  10.  
  11. Use back-up wrench to connect the fuel feed and return pipe to the fuel rail.
  12.  
  13. Install the right (rear) and left (front) valve rocker cover. Refer to the procedure in this section.
  14.  
  15. Install the upper intake manifold, as outlined earlier. Make sure to follow the proper torque sequence.
  16.  
  17. Fill the coolant system.
  18.  
  19. Connect the negative battery cable and check for leaks.
  20.  

3.8L Engine

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Properly relieve the fuel system pressure, as outlined in Fuel System of this repair guide.
  6.  
  7. Remove the air cleaner intake duct and box assembly.
  8.  

See Figures 4, 5, 6 and 7

Click image to see an enlarged view

Fig. Fig. 4: Remove the air filter box and duct as an assembly

  1. Tag and disconnect the spark plug wires from the right side of the engine, then set them aside.
  2.  
  3. Remove the fuel rail, as outlined in Fuel System of this repair guide.
  4.  



Click image to see an enlarged view

Fig. Fig. 5: Unfasten the fuel rail mounting bolts



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Fig. Fig. 6: Make sure to remove all of the bolts that secure the fuel rail to the manifold



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Fig. Fig. 7: The fuel delivery system can be lifted to gain access to the manifold without total disassembly

  1. Remove the exhaust crossover heat shield.
  2.  
  3. Remove the cable bracket to cylinder head mounting bolt.
  4.  

See Figure 8

Click image to see an enlarged view

Fig. Fig. 8: Remove the throttle body bracket. Note the location of the MAF sensor (A) TP sensor (B) and IAC valve (C), mounted on the throttle body.

  1. Remove the serpentine belt.
  2.  
  3. Remove the power steering pump support bracket.
  4.  
  5. Loosen the alternator mounts and slide it to gain access.
  6.  
  7. Remove the alternator mounting bracket.
  8.  
  9. Remove the heater pipes.
  10.  
  11. Disconnect the by-pass hose.
  12.  

See Figures 9, 10, 11 and 12

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Fig. Fig. 9: The by-pass hose and heater pipe will have to be disconnected to remove the lower intake manifold.



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Fig. Fig. 10: Loosen the clamp retaining screw ...



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Fig. Fig. 11: . . then slide the hose off the nipple



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Fig. Fig. 12: Remove the bolt holding the heater pipe into the manifold: The O-ring (arrow) should be replaced before re-assembly

  1. Remove the EGR valve outlet pipe.
  2.  
  3. Unfasten the retaining bolts, then remove the intake manifold from the engine.
  4.  

See Figures 13 through 21

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Fig. Fig. 13: If necessary separate the throttle body from the intake manifold. There are usually three mounting studs.



Click image to see an enlarged view

Fig. Fig. 14: Removing the upper intake manifold, without total disassembly of the fuel system.



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Fig. Fig. 15: Looking into the throat of the upper intake manifold; Note the gasket



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Fig. Fig. 16: View of the underside of the upper intake manifold



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Fig. Fig. 17: View of the lower intake manifold installed on the engine



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Fig. Fig. 18: Unfasten the lower intake manifold bolts



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Fig. Fig. 19: Unplug the sensor electrical connector; it is not necessary to remove it for manifold removal



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Fig. Fig. 20: After removing all of the retainers, lift the intake manifold from the engine. Note that the upper hose was disconnected from the radiator



Click image to see an enlarged view

Fig. Fig. 21: Exploded view of the upper and lower intake manifolds and gaskets-3.8L engine

  1. Clean the cylinder block, heads, and intake manifold sealing surface of all oil with a suitable solvent.
  2.  

To install:
  1. Apply a suitable RTV sealant to the ends of the manifold seals.
  2.  
  3. Clean the intake manifold bolts and bolt holes of old adhesive compound.
  4.  
  5. Position a new intake gasket, then install intake manifold. Tighten the mounting bolts, in two passes, to 11 ft. lbs. (15 Nm) following the sequence given in the accompanying figure.
  6.  

See Figure 22

Click image to see an enlarged view

Fig. Fig. 22: Intake manifold bolt tightening sequence-3.8L engine

  1. Install the EGR valve outlet pipe.
  2.  
  3. Reconnect the by-pass hose.
  4.  
  5. Install the alternator bracket, position the alternator and tighten the bolts.
  6.  
  7. Install the serpentine belt.
  8.  
  9. Install the power steering pump support bracket.
  10.  
  11. Install the cable bracket to cylinder head mounting bolt.
  12.  
  13. Replace the exhaust crossover heat shield.
  14.  
  15. Install the fuel rail, as outlined in Fuel System of this repair guide.
  16.  
  17. Replace the plug wires in their respective positions on the right side of the engine.
  18.  
  19. Install the air duct.
  20.  
  21. Fill the coolant system.
  22.  
  23. Connect the negative battery cable.
  24.  
  25. Check for leaks.
  26.  

 
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