GMC 12550122 Engine Exhaust Manifold

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To take off the exhaust manifold, first disconnect the negative battery cable and lift the vehicle on jackstands. Apply penetrating oil to the exhaust pipe-to-manifold studs and nuts then remove the nuts which hold the exhaust pipe(s) to the manifold(s). On TBI models, this will involve removing the air cleaner assembly and also heat stove pipe on right side manifold. Disconnecting spark plug wires and brackets as well as unbolt air conditioning compressor with its bracket then leave only one screw that you loosened for last. Remove oil dipstick and tube bracket. Removing rear brace from alternator (unbolt), spark plug wires, EGR pipe (1996 and later models) etc. Take out power steering pump pulley after removing rear power steering bracket by removing mounting bolts. Bend lock tabs back, then remove mounting bolts followed by separation of exhaust from cylinder head. Clean both surfaces where manifold mates with cylinder head. Place it over cylinder head onto which it is mounted with installing three fastening screws in a sequence which divides them into three equal parts. Reassemble everything else that remains and make sure there are no leaks when cranking up engine.

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

Remove the cable from the negative battery terminal.

After reassembling the remaining components, it is important to check for exhaust leaks when starting the engine.

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

Penetrating oil should be applied to the fastener threads.

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

The oxygen sensor.