GMC 12555082 Engine Exhaust Manifold

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Remove the cable from the negative battery terminal. Remove the air cleaner assembly and duct. Remove the oxygen sensor from the manifold. Raise the vehicle and securely support it on jackstands. Disconnect the exhaust pipe from the exhaust manifold. You may need to apply penetrating oil to the fastener threads as they are usually corroded. On air-conditioned models, remove the air conditioning compressor rear mount, and remove the nut and the oil filler tube without disconnecting the lines. Remove the nut on the oil filler tube assembly. Remove the exhaust manifold nuts and separate the exhaust manifold from the engine. Remove the exhaust manifold gasket. Before installing the manifold, clean the gasket mating surfaces on the cylinder head and manifold. Remove all old gasket material and carbon deposits. Check the bolt threads for damage. Place a new exhaust manifold gasket in position on the cylinder head, then place the manifold in position and tighten the mounting nuts. Install the remaining components in the reverse order of removal. Start the engine and check for exhaust leaks between the manifold and cylinder head, and between the manifold and exhaust pipe.

On the right side manifold, the air cleaner assembly and the heat stove pipe on TBI models need to be removed.

The oxygen sensor.

After removing the exhaust manifold, the manifold and cylinder head mating surfaces should be cleaned.

The manifold should be placed in position and the mounting nuts should be tightened.

The manifold should be positioned on the cylinder head and the mounting bolts should be installed, tightening them in three equal steps.

To remove the rear power steering bracket, the power steering pump pulley and mounting bolts need to be removed.

The remaining components should be installed in the reverse order of removal.