GM Cadillac 1967-1989 Repair Guide

Intake Manifold

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REMOVAL & INSTALLATION



Carbureted Engines

See Figures 1, 2, 3 and 4

  1. Remove the negative battery terminal, air cleaner, heat tube and PCV valve.
  2.  
  3. Disconnect the throttle and cruise control linkages.
  4.  
  5. Remove the coil wires or HEI electrical connector from the distributor.
  6.  
  7. Remove the distributor cap and the ignition wires. Mark the position of the rotor and the wires for reinstallation.
  8.  
  9. Disconnect the temperature sending unit and the electrical connection from the air conditioning compressor. Remove the SCS solenoid (if so equipped).
  10.  
  11. Disconnect the two wires from the downshift switch. On 1977 and later models disconnect the throttle return spring and downshift switch bracket. Disconnect the electrical choke (if so equipped).
  12.  
  13. Remove the plug from the anti-dieseling solenoid and any other necessary electrical connection.
  14.  
  15. Disconnect the power brake booster vacuum line and the modulator vacuum line.
  16.  
  17. Disconnect the fuel line from the carburetor.
  18.  
  19. Disconnect the vacuum advance line (if so equipped) and the canister purge hoses and position them out of the way.
  20.  
  21. Remove the air conditioning compressor and position it out of the way. DO NOT disconnect the refrigerant lines.
  22.  
  23. Disconnect the coolant by-pass hose at the manifold (if so equipped).
  24.  
  25. Remove the carburetor.
  26.  
  27. Remove the manifold bolts and remove the manifold.
  28.  
  29. Installation is the reverse of removal, taking note of the following:
    1. Coat the ends of the new rubber end seals with RTV sealer. Place the seals on the front and rear of the engine block. Position the seal tabs in the hole provided. Tuck the beveled ends of the seals under the edge of the cylinder head.
    2.  
    3. Apply a thin layer of graphite along both sides of the top fiber part of the intake gasket.
    4.  
    5. Position the intake manifold on the cylinder heads by lowering it straight down. The manifold is centered evenly by tightening the third bolt from each side. Tighten all the mounting bolts to the specifications listed in the Torque Specification Chart.

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      Fig. Fig. 1: Intake manifold gaskets and seals - 8-307 engine



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      Fig. Fig. 2: Intake manifold torque sequence - 8-307 engine



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      Fig. Fig. 3: Intake manifold torque sequence - 6-252 engine



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      Fig. Fig. 4: Intake manifold torque sequence - 8-350 engine

    6.  

  30.  

Fuel Injected Engines

See Figures 5, 6, 7, 8, 9, 10, 11, 12 and 13 EXCEPT 8-250 AND 8-273 ENGINES

  1. Disconnect the negative battery cable and remove the air cleaner and crankcase filter.
  2.  
  3. Disconnect the throttle cable and cruise control linkage at the throttle body. Remove the cable from the bracket and move it aside.
  4.  
  5. Disconnect the coolant temperature switch wire, the HEI wire, speed sensor wire, downshift switch wire, and the injector wiring harness from the fuel rail brackets and move the harness out of the way.
  6.  
  7. Disconnect the two vacuum hoses from the throttle body to the thermal vacuum switch (TVS).
  8.  
  9. Disconnect the vacuum hoses and power brake pipe from the rear of the throttle body.
  10.  
  11. Bleed the pressure from the fuel delivery system, as outlined in the Fuel Pump Removal section in Fuel System . Using a back-up wrench to avoid kinking the fuel line, disconnect the fuel line from the fuel rail.
  12.  
  13. Disconnect the EGR solenoid wires, air temperature sensor wire and the MAP sensor vacuum hose.
  14.  
  15. Remove the PCV valve from the rocker cover and move it out of the way.
  16.  
  17. Remove the spark plug wires and the distributor cap.
  18.  
  19. On the 425 and 500 engines, disconnect the front fuel rail. Be careful not to kink any of the lines. On the 350 and 368 engine, drain the radiator, disconnect the upper radiator hose, the thermostat bypass hose and the heater hose at the rear of the manifold.
  20.  
  21. Remove the air conditioning compressor and tie it out of the way. Do not disconnect the refrigerant lines.
  22.  
  23. Remove the fuel feel (DFI) and return hose from the fuel pressure regulator.
  24.  
  25. Remove the intake manifold retaining screws and remove the manifold. Do not pry or lift the manifold by the fuel rails or their mounting brackets.
  26.  

To install:
  1. Clean all gasket material from the mating surfaces of the manifold, cylinder heads and block.
  2.  
  3. Place new rubber intake manifold seals over the rails at the front and rear of the cylinder block. The tabs on the gasket should be positioned in the holes in the rails and the beveled ends of the gasket tucked into the slot at the mating of the head and rail.
  4.  

For the 8-368 cu. in. engine proceed to Steps 19-21.

  1. Apply gasket sealer to the sheet metal gasket-shield on the engine. The holes in the gasket should engage the dowel pins on the cylinder heads. Be careful not to use too much sealer near the injector tips.
  2.  
  3. Carefully position the manifold on the top of the engine. Install and tighten the intake manifold retaining screws to the specified torque.
  4.  
  5. Assemble and install the remaining components in the reverse order of removal.
  6.  

To insure a leak free installation the following steps should be taken on the 8-368 cu. in. engine.

  1. Coat the ends of the new rubber end seals with RTV sealer. Place the seals on the front and rear of the cylinder block. Position the seal tabs in the holes provided. Tuck the beveled ends of the seals under the edge of the cylinder head.
  2.  
  3. Apply a thin layer of graphite along both sides of the top fiber part of the intake gasket. Install intake gasket.
  4.  
  5. Position the intake manifold on the cylinder heads by lowering straight down. The manifold is centered evenly by tightening the third bolt from each side. Tighten all mounting bolts to 30 ft. lbs. (41 Nm).
  6.  

1982-85 8-250 ENGINE
  1. Drain the coolant from the radiator and disconnect the upper radiator hose from the upper thermostat housing.
  2.  
  3. Disconnect the electrical connections from the following: Coolant sensor, MAT sensor, throttle position sensor, the 12 volt feed wire and the 4 way connector, ISC motor and the injectors.
  4.  
  5. Disconnect the heater hose from the rear of the intake manifold.
  6.  
  7. Disconnect the fuel lines from the throttle body.
  8.  
  9. Mark and remove the distributor assembly.
  10.  
  11. Remove the rocker arm covers then remove the rocker arm support with the rocker arms intact by removing the five nuts which attach the support to the stud-headed head bolts. Keep the pushrods in sequence so they may be reassembled in their original position.
  12.  
  13. Partially disconnect the air conditioning compressor and move to one side without discharging the air conditioning system.
  14.  
  15. Remove the vacuum harness connections from the TVS at the rear of the intake manifold.
  16.  
  17. Remove the 16 intake manifold bolts and remove the two bolts securing the lower thermostat housing to the front cover.
  18.  
  19. Bend the front and rear engine lift brackets out of the way then remove the intake manifold and lower thermostat housing as an assembly by lifting straight up.
  20.  

To install:
  1. Position new gaskets to the cylinder head and crankcase.
  2.  

The right intake manifold gasket for 1984-85 models contains a restrictor which controls the flow of exhaust gas into the intake manifold. The manifold gasket with the restrictor has "RIGHT BANK" printed on it to aid in identification. It is important to use the correct gasket.

  1. Apply RTV sealant to the four corners where the end seals will meet the side gaskets, place the end seals into position, then again apply RTV sealant at the four corners.
  2.  
  3. Using new O-rings, assemble the lower thermostat housing and water transfer pipe to the intake manifold.
  4.  
  5. Lightly coat a new water pump to thermostat O-ring with chassis grease and position the O-ring the the water pump outlet. Do not insert the O-ring into the thermostat housing bore.
  6.  
  7. Carefully lower the intake manifold/thermostat housing assembly straight down onto the engine so that the dowel pins in the crankcase engage the intake manifold and the thermostat housing is positioned over the water pump outlet.
  8.  
  9. Loosely install the 16 intake manifold bolts. Four different length bolts are used. Engine lift hooks are installed under the front right and left rear mounting screws. Bolt lengths may differ on earlier years, use the correct bolts. Torque the bolts to values and the sequence shown in the illustrations.
  10.  

Final intake manifold torque must not exceed 22 ft. lbs. (30 Nm).

  1. Secure the thermostat housing to front cover with the two bolts. Tighten the stud headed bolt to 30 ft. lbs. (41 Nm) and the tapping screw to 8 ft. lbs. (11 Nm).
  2.  
  3. Connect the water hose to the nipple at the rear of the intake manifold.
  4.  
  5. Connect the upper radiator hose and refill the cooling system.
  6.  
  7. Install the distributor as outlined earlier in this section.
  8.  
  9. Install the air conditioning compressor.
  10.  
  11. Install the pushrods in the positions from which they were removed. Make sure they are fully seated in their valve lifters. Since this cannot be seen, the feel for this condition must be developed.
  12.  
  13. Position the valve train support with the rocker arms and pivots installed over the five stud-headed head bolts. Carefully position the pushrod into the seat in each rocker arm and loosely install the five remaining nuts, recheck the pushrods for correct position and tighten the retaining nuts alternately and evenly checking the position of the pushrods from time to time. When the nuts are all the way down, tighten to 35 ft. lbs. (47 Nm).
  14.  
  15. Install both rocker arm covers.
  16.  
  17. Make all vacuum connections.
  18.  
  19. Connect the electrical connections to the following: Coolant sensor, MAT sensor, throttle position sensor, the 12 volt feed wire and the 4 way connector, ISC motor and the injectors.
  20.  
  21. Start the engine and adjust the ignition timing as necessary. Check for leaks.
  22.  

1986-89 8-250 AND 8-273 ENGINES
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Drain the engine coolant.
  6.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the 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 right side cross brace.
  2.  
  3. Remove the coolant recovery tank.
  4.  
  5. Remove the drive belts.
  6.  
  7. Remove the idler pulley assembly.
  8.  
  9. Remove the power steering line brace connected to the right cylinder head.
  10.  
  11. Disconnect the power steering pump and tensioner bracket assembly and position it toward the front of the engine.
  12.  
  13. Tag and disconnect the electrical leads at the alternator and then remove the alternator.
  14.  
  15. Disconnect the cruise control and its bracket. Disconnect the TV cables. Position both assemblies out of the way.
  16.  
  17. Tag and disconnect all wires, hoses and lines which might interfere with manifold removal.
  18.  
  19. Disconnect the upper radiator and heater hoses.
  20.  
  21. Disconnect the spark plug wire protectors, remove the distributor cap and position the cap and wire assembly out of the way.
  22.  
  23. Mark the position of the distributor rotor and remove the distributor.
  24.  

Never rotate the engine with the distributor removed.

  1. Bleed the fuel pressure at the fuel line Schrader valve as detailed in Emission Controls and then disconnect the fuel and vacuum lines at the throttle body.
  2.  
  3. Disconnect the vacuum supply solenoid and its lines.
  4.  
  5. Remove the valve covers and the rocker arms and pushrods.
  6.  

The pushrods should be marked so that they may be installed in their original sequence.

  1. Remove the mounting bolts and remove the intake manifold.
  2.  

To install:
  1. Remove all traces of old gasket and/or sealant material.
  2.  
  3. Install new end seals. Apply RTV sealant to the ends that will meet with the side gaskets.
  4.  
  5. Install new manifold gaskets and position the manifold.
  6.  
  7. Tighten the manifold bolts in the order shown in the illustration, to the proper torque. Refer to the Torque Specification Chart.
  8.  
  9. Install the pushrods in the positions from which they were removed. Make sure they are fully seated in their valve lifters. Since this cannot be seen, the feel for this condition must be developed.
  10.  
  11. Position the valve train support with the rocker arms and pivots installed over the five stud-headed head bolts. Carefully position the pushrod into the seat in each rocker arm and loosely install the five remaining nuts, recheck the pushrods for correct position and tighten the retaining nuts alternately and evenly checking the position of the pushrods from time to time. When the nuts are all the way down, tighten to 35 ft. lbs. (47 Nm).
  12.  
  13. Install both rocker arm covers.
  14.  
  15. Make all vacuum connections.
  16.  
  17. Connect the electrical connections to the following: Distributor, oil pressure switch, coolant sensor, EGR solenoid, ISC motor, throttle position sensor, EFE grid, MAP sensor, ISC motor and the injectors.
  18.  
  19. Connect the cruise control and its bracket. Connect the TV cables.
  20.  
  21. Install the alternator and bracket.
  22.  
  23. Install the power steering and tensioner assembly.
  24.  
  25. Install the power steering line brace to the right hand cylinder head.
  26.  
  27. Install the accessory drive belt.
  28.  
  29. Install the coolant reservoir tank.
  30.  
  31. Install the right hand cross bar brace.
  32.  
  33. Fill the cooling system.
  34.  
  35. Install the air cleaner assembly.
  36.  
  37. Install the negative battery cable.
  38.  



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Fig. Fig. 5: Intake manifold gaskets and seals - 8-250, 8-273 engines



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Fig. Fig. 6: Intake manifold bolt size and location - 1983-84 8-250 engine



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Fig. Fig. 7: Intake manifold bolt size and location - 1985 8-250 engine



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Fig. Fig. 8: Intake manifold bolt size and location - 1986-87 8-250 engine



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Fig. Fig. 9: Intake manifold bolt size and location - 8-273 engine



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Fig. Fig. 10: Intake manifold bolt torque sequence - 8-273 engine



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Fig. Fig. 11: View of the rocker arm support and intake manifold



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Fig. Fig. 12: Removing the intake manifold



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Fig. Fig. 13: View of the engine assembly with the intake manifold removed

Diesel Engines

See Figures 14 and 15

  1. Remove the air cleaner.
  2.  
  3. Drain the radiator. Loosen the upper bypass hose clamp, remove the thermostat housing bolts, and remove the housing and the thermostat from the intake manifold.
  4.  
  5. Remove the breather pipes from the rocker covers and the air crossover. Remove the air crossover.
  6.  
  7. Disconnect the throttle rod and the return spring. If equipped with cruise control, remove the servo.
  8.  
  9. Remove the hairpin clip at the bellcrank and disconnect the cables. Remove the throttle cable from the bracket on the manifold; position the cable away from the engine. Disconnect and label any wiring as necessary.
  10.  
  11. Remove the alternator bracket if necessary. If equipped with air conditioning, remove the compressor mounting bolts and move the compressor aside, without disconnecting any of the hoses. Remove the compressor mounting bracket from the intake manifold.
  12.  
  13. Disconnect the fuel line from the pump and the fuel filter. Remove the fuel filter and bracket.
  14.  
  15. Remove the fuel injection pump and lines. Fuel System for procedures.
  16.  
  17. Disconnect and remove the vacuum pump or oil pump drive assembly from the rear of the engine.
  18.  
  19. Remove the intake manifold drain tube.
  20.  
  21. Remove the intake manifold bolts and remove the manifold. Remove the adapter seal. Remove the injection pump adapter.
  22.  

To install:
  1. Clean the mating surfaces of the cylinder hears and the intake manifold using a putty knife.
  2.  
  3. Coat both sides of the gasket surface that seal the intake manifold to the cylinder heads with G.M. sealer #1050026 or the equivalent. Position the intake manifold gaskets on the cylinder heads. Install the end seals, making sure that the ends are positioned under the cylinder heads.
  4.  
  5. Carefully lower the intake manifold into place on the engine.
  6.  
  7. Clean the intake manifold bolts thoroughly, then dip them in clean engine oil. Install the bolts and tighten to 15 ft. lbs. (20 Nm). in the sequence shown. Next, tighten all the bolts to 30 ft. lbs. (41 Nm), in sequence, and finally tighten to 40 ft. lbs. (54 Nm) in sequence.
  8.  
  9. Install the intake manifold drain tube and clamp.
  10.  
  11. Install injection pump adapter. Fuel System . If a new adapter is not being used, skip steps 4 and 9.
  12.  



Click image to see an enlarged view

Fig. Fig. 14: Intake manifold torque sequence - 8-350 diesel engine



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Fig. Fig. 15: Diesel engine manifold and gasket

 
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