GM Full Size Vans 1967-1986 Repair Guide

Intake Manifold

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REMOVAL & INSTALLATION



Inline 6-Cylinder Engines

1974 and earlier 250 and 292 six cylinder engines use a combined intake and exhaust manifold, both of which are removed together. 1976 and later engines have an intake manifold which is cast integrally with the cylinder head and cannot be removed.

  1. Remove the air cleaner assembly and air ducts.
  2.  
  3. Tag and disconnect the throttle linkage at the carburetor. Tag and disconnect the fuel line, vacuum lines, hoses, and electrical connections.
  4.  
  5. Disconnect the transmission downshift linkage (if equipped), and remove the PCV valve from the rocker cover. On models equipped with air injection, disconnect the air supply hose from the check valve on the air injection manifold.
  6.  
  7. Remove the carburetor, with spacer and heat shield (if equipped).
  8.  
  9. Spray the nuts and bolts connecting the exhaust manifold to the exhaust pipe with a rust penetrant, as these are usually quite difficult to remove. Unbolt the exhaust manifold from the pipe.
  10.  

It may be necessary to remove the generator rear bracket and/or A/C bracket on some models.

  1. Unbolt the manifold bolts and clamps, and remove the manifold assembly.
  2.  
  3. If you intend to separate the manifolds, remove the single bolt and two nuts at the center of the manifold assembly.
  4.  
  5. Installation is the reverse of removal. When assembling the manifolds, install the connecting bolts loosely first. Place the manifolds on a straight, flat surface and hold them securely during the tightening, this assures the proper mating of surfaces when the manifold assembly is fastened to the head. Stress cracking could occur if the manifolds are not assembled first in this manner. On all manifolds, always use new gaskets between the manifolds and cylinder head.
  6.  

V6 and V8 Engines

EXCEPT DIESEL ENGINES

See Figures 1 through 9

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Fig. Fig. 1: Remove the water hoses from the intake manifold



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Fig. Fig. 2: Disengage all vacuum hoses from the intake manifold



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Fig. Fig. 3: Unfasten the intake manifold retaining bolts



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Fig. Fig. 4: Use a prytool to separate the intake manifold from the cylinder heads ...



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Fig. Fig. 5: ... then remove the manifold from the engine



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Fig. Fig. 6: Remove the old gasket from the engine



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Fig. Fig. 7: Using a gasket scraper, remove any old gasket residue and dirt



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Fig. Fig. 8: Exploded view of gasoline V8 intake manifold mounting and its related components



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Fig. Fig. 9: Intake manifold bolt tightening sequence

  1. Drain the cooling system.
  2.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the air cleaner assembly.
  2.  
  3. Remove the thermostat housing and the bypass hose. It is not necessary to remove the top radiator hose from the thermostat housing.
  4.  
  5. Disconnect the heater hose at the rear of the manifold.
  6.  
  7. Disconnect all electrical connections and vacuum lines from the manifold. Remove the EGR valve if necessary.
  8.  
  9. On vehicles equipped with power brakes remove the vacuum line from the vacuum booster to the manifold.
  10.  
  11. Remove the distributor (if necessary).
  12.  
  13. Remove the fuel line to the carburetor.
  14.  
  15. Remove the carburetor linkage.
  16.  
  17. Remove the carburetor.
  18.  
  19. Remove the intake manifold bolts. Remove the manifold and the gaskets. Remember to reinstall the O-ring between the intake manifold and timing chain cover during assembly, if so equipped.
  20.  
  21. Installation is the reverse of removal. Use plastic gasket retainers to prevent the manifold gasket from slipping out of place, if so equipped. On the small block V8s, place a 3 / 16 in. (4.8mm) bead of RTV type silicone sealer on the front and rear ridges of the cylinder block-to-manifold mating surfaces. Extend the bead 1 / 2 in. (12.7mm) up each cylinder head to seal and retain the manifold side gaskets.
  22.  

Before installing the intake manifold, be sure that the gasket surfaces are thoroughly clean.

DIESEL ENGINES

See Figure 10

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Fig. Fig. 10: Exploded view of the diesel intake manifold mounting and tightening sequence

  1. Disconnect both batteries.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Remove the crankcase ventilator tubes, and disconnect the secondary fuel filter lines. Remove the secondary filter and adaptor.
  6.  
  7. Loosen the vacuum pump hold-down clamp and rotate the pump to gain access to the nearest manifold bolt.
  8.  
  9. Remove the EPR/EGR valve bracket, if equipped.
  10.  
  11. Remove the rear air conditioning bracket, if equipped.
  12.  
  13. Remove the intake manifold bolts. The injection line clips are retained by these bolts.
  14.  
  15. Remove the intake manifold.
  16.  


WARNING
If the engine is to be further serviced with the manifold removed, install protective covers over the intake ports.

  1. Clean the manifold gasket surfaces on the cylinder heads and install new gaskets before installing the manifold.
  2.  

The gaskets have an opening for the EGR valve on light duty installations. An insert covers this opening on heavy duty installations.

  1. Install the manifold. Torque the bolts in the sequence illustrated.
  2.  
  3. The secondary filter must be filled with clean diesel fuel before it is reinstalled.
  4.  
  5. Reverse the remaining removal procedures to complete the installation.
  6.  

 
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