GM Full-Size Trucks 1980-1987 Repair Guide

Exhaust Manifold

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REMOVAL & INSTALLATIONIn-line 6-Cylinder



250 (4.1L) ENGINE

See Figure 1

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect and remove the air cleaner assembly, including the carburetor preheat tube.
  4.  
  5. Remove power steering pump bracket and AIR pump brackets if equipped.
  6.  
  7. Remove PAIR pipes.
  8.  
  9. Disconnect the exhaust pipe at the exhaust manifold. You will probably have to use a liquid rust penetrant to free the bolts.
  10.  
  11. Remove the engine oil dipstick bracket bolt.
  12.  
  13. Liberally coat the manifold nuts with a rust penetrating lubricant. Remove the exhaust manifold bolts and remove the manifold.
  14.  

To install:
  1. Mount the manifold on the cylinder head and start all bolts.
  2.  
  3. Torque the bolts to specification using the torque sequence illustrated. Complete the installation by reversing the removal procedure.
  4.  



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Fig. Fig. 1: 250 (4.1L) in-line six exhaust manifold torque sequence

292 (4.8L) ENGINE
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly and air ducts.
  4.  
  5. Tag and disconnect the throttle linkage at the carburetor. Tag and disconnect the fuel line, vacuum lines, hoses, and electrical connections.
  6.  
  7. 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.
  8.  
  9. Remove the carburetor, with spacer and heat shield (if equipped).
  10.  
  11. 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.
  12.  

It may be necessary to remove the generator rear bracket and/or air conditioning compressor 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.  

To install:
  1. Before reassembling the two manifolds, check the exhaust manifold for warpage by laying a straight edge across the full length of the exhaust ports. If at any point a gap of 0.030 inch (0.080 mm) or more exists, the manifold will not likely seat properly and will require replacement.
  2.  
  3. When reassembling the manifolds, install the connecting bolts loosely first. Place the manifolds on a straight, flat surface and hold them securely during 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.
  4.  
  5. Position a manifold gasket over manifold end studs on the cylinder head. On all manifolds, always use new gaskets.
  6.  
  7. Align and install manifold assembly to the cylinder head. Initially tighten all bolts finger tight.
  8.  
  9. Torque all manifold to cylinder head bolts to 40 ft. lbs. (55 Nm).
  10.  
  11. Complete manifold attachment by tightening the inlet to exhaust manifold bolt and the two nuts at the center of the manifold to 45 ft. lbs. (61 Nm).
  12.  
  13. Reconnect exhaust pipe to manifold using a new packing.
  14.  
  15. Install the carburetor, with spacer and heat shield (if equipped).
  16.  
  17. Reconnect the transmission downshift linkage, if equipped, and reinstall the PCV valve hose from the rocker cover. On models equipped with air injection, reconnect the air supply hose from the check valve on the air injection manifold.
  18.  
  19. Reconnect the throttle linkage at the carburetor. Reconnect the fuel line, vacuum lines, hoses, and electrical connections.
  20.  
  21. Reinstall the air cleaner assembly and air ducts.
  22.  
  23. Reconnect negative battery cable.
  24.  

Gasoline V6 and V8s

See Figures 2, 3, 4, 5, 6, 7 and 8

Tab locks are used on the front and rear pairs of bolts on each exhaust manifold. When removing the bolts, straighten the tabs from beneath the car using a suitable tool. When installing the tab locks, bend the tabs against the sides of the bolts, not over the top of the bolt.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Remove the hot air shroud, if equipped.
  6.  
  7. Loosen the alternator and remove its lower bracket.
  8.  
  9. Raise the truck and support it safely using jackstands. It will be easiest for the following steps if the truck is supported at a height which will allow for both underhood and undervehicle access.
  10.  
  11. Disconnect the crossover pipe from both manifolds by remove the stud nuts, carefully lowering the pipe and by removing the pipe collars (if equipped).
  12.  



Click image to see an enlarged view

Fig. Fig. 2: Be careful when removing the crossover pipe stud nuts, some applications are spring loaded and may jump loose while unthreading



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Fig. Fig. 3: Some applications use a collar to achieve a better seal between the crossover pipe and the exhaust manifold

  1. Lower the vehicle, as necessary, for underhood access.
  2.  

On models with air conditioning it may be necessary to remove the compressor, and tie it out of the way. Do not disconnect the compressor lines.

  1. Remove the manifold bolts and remove the manifold(s). Some models have lock tabs on the front and rear manifold bolts which must be removed before removing the bolts. These tabs can be bent with a drift pin.
  2.  



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Fig. Fig. 4: To loosen the exhaust manifold mounting nuts you will need a deep socket or a box wrench



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Fig. Fig. 5: Once the nuts are removed, carefully pull the manifold back and free from the studs



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Fig. Fig. 6: Here the exhaust manifold has just been removed along with 2 of its 3 gaskets

  1. Reverse the above to install. Torque the bolts to specifications and bend the tab washers over the heads of all bolts.
  2.  



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Fig. Fig. 7: Plastic manifold gasket retainers, gasoline V8's



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Fig. Fig. 8: Gasoline V8 exhaust manifold with hot air shrouds

8-350 Diesel V8

LEFT SIDE
  1. Remove the air cleaner and cover the air crossover with a protective plate, screen or cover.
  2.  
  3. Remove the lower generator bracket.
  4.  
  5. Jack up the truck and safely support it with jackstands.
  6.  
  7. Remove the exhaust pipe at the manifold flange.
  8.  
  9. Lower the truck.
  10.  
  11. Remove the exhaust manifold from above.
  12.  
  13. Reverse the above procedure to install. Torque the manifold nuts and bolts according to the illustration.
  14.  

RIGHT SIDE
  1. Jack up the truck and safely support it with jackstands.
  2.  
  3. Disconnect the exhaust pipe at the manifold flange.
  4.  
  5. Remove the manifold.
  6.  
  7. Reverse the above procedure to install, tightening the manifold bolts according to the accompanying illustration.
  8.  

8-379 Diesel V8

See Figure 9



Click image to see an enlarged view

Fig. Fig. 9: 379 diesel intake manifold gasket mounting and bolt torque sequence

RIGHT SIDE
  1. Disconnect the batteries.
  2.  
  3. Jack up the truck and safely support it with jackstands.
  4.  
  5. Disconnect the exhaust pipe from the manifold flange and lower the truck.
  6.  
  7. Disconnect the glow plug wires.
  8.  
  9. Remove the air cleaner duct bracket.
  10.  
  11. Remove the glow plug wires.
  12.  
  13. Remove the manifold bolts and remove the manifold.
  14.  
  15. To install, reverse the above procedure and torque the bolts to 25 ft. lbs.
  16.  

LEFT SIDE
  1. Disconnect the batteries.
  2.  
  3. Remove the dipstick tube nut, and remove the dipstick tube.
  4.  
  5. Disconnect the glow plug wires.
  6.  
  7. Jack up the truck and safely support it with jackstands.
  8.  
  9. Disconnect the exhaust pipe at the manifold flange.
  10.  
  11. Remove the manifold bolts. Remove the manifold from underneath the truck.
  12.  
  13. Reverse the above procedure to install. Start the manifold bolts while the truck is jacked up first. Tighten the bolts to 25 ft. lbs.
  14.  

 
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