GMC 12552325 Engine Exhaust Manifold Assembly

First, disconnect the cable from the negative battery terminal and on the models with audio system there is an anti-theft feature that should be turned off before disconnecting the battery. Next, unload the engine cover and, at the exhaust manifold, undo the heat stove pipe. Lift the vehicle and then support it with jackstands then remove the oxygen sensor. Label and remove the 4 wires of spark plug, tied up clear of the engine. Remove the nut/bolt that connects the exhaust pipe to the exhaust manifold using a breaker bar/extension bar and apply penetrating oil if there is rust on threads and then drag the exhaust pipe down and use wire and hang it on the frame . Bolt covers and shrouds at the rear, then take off the rear air conditioning compressor bracket before removing the bolts on the exhaust manifold end and the manifold center bolts to isolate manifold from the engine. Remove the exhaust manifold gasket, and check the gasket joining surfaces on the cylinder head and manifold for cleanliness and absence of all existing gasket materials, and carbon deposits on it and also check whether the joining bolt threads of manifold are in good condition. A new exhaust manifold gasket should be applied to the cylinder head and the manifold well seated before the mounting bolts are tightened with fingers just enough to hold the manifold in place. Loosen the bolts gradually in the correct sequence until the reach the torque you want to be at. Join the exhaust pipe back and the air conditioning compressor bracket back and then lower the car. Last of all, put back the remaining pieces in a reverse order of their removal, crank the engine, and look for exhaust loss at the junction between the manifold and cylinder head and between the manifold and the exhaust pipe.