GMC 12567679 Manifold Assembly, Intake

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Disconnect the cable from the negative battery terminal. Remove the air intake duct assembly. Remove the PCV valve and hose connecting the intake manifold to the valve cover. Remove the upper intake manifold (1997 and earlier MFI models only). Tag and disconnect all electrical connectors at the throttle body and manifold. Remove the fuel lines and any wiring attached to the lower intake manifold. Remove the fuel rail bracket. Remove the spark plug wires from the coil pack. Mark the spark plug wires for reassembly. Pull them up through the intake manifold and lay them over the left side of the engine. Remove the bolt holding the heater hose tube to the right rear of the manifold. Remove the mounting nuts and separate the manifold from the cylinder head. Remove the EGR tube for cleaning. Remove the old gasket and transfer all components still attached to the old manifold to the new one. Before installing the manifold, clean the cylinder head and manifold gasket surfaces. Apply a thin coat of RTV sealant to the intake manifold and cylinder head mating surfaces. Place a new gasket on the manifold, hold the manifold in position against the cylinder head, and install the mounting nuts finger tight. Tighten the mounting nuts in several steps and in the correct sequence. Install the remaining components in the reverse order of removal.

Before installing the manifold, you should clean the cylinder head and manifold gasket surfaces and apply a thin coat of RTV sealant to the intake manifold and cylinder head mating surfaces.

Follow similar steps starting from removing the upper fan shroud, air cleaner assembly, draining the cooling system, and disconnecting the upper radiator and heater hoses. Unbolt the EGR valve, move heater hoses, and remove the ignition coil. Remove the small brace from the air conditioning compressor to the intake manifold and turn the engine to TDC for number 1 piston before removing the distributor.

Remove the two rear braces from the drive belt tensioner, unbolt the emission relays bracket, and proceed to remove the spark plug wires, coil, and distributor, marking the distributor rotor's relationship before removal. Disconnect the fuel lines at the TBI unit, remove accelerator, cruise control, and TV cables from the manifold, detach the vacuum brake booster pipe, and label and disconnect various lines and wires at the manifold and TBI unit. Move the EGR hose and begin loosening the manifold mounting bolts, followed by prying up the front of the manifold after removing all bolts.