GMC 12557359 Engine Exhaust Manifold

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Disconnect the negative cable from the battery. Remove the air cleaner assembly for access to the right manifold. If you are removing the manifold with the oxygen sensor in it, disconnect the wire to the sensor. Remove the air management tube at the check valve and the pipe bracket from the manifold stud, if equipped. Remove the alternator and power steering braces from the left exhaust manifold. Disconnect the spark plug wires and the spark plugs. If there is any danger of mixing the plug wires up, we recommend labeling them with small pieces of tape. If you are removing the right manifold on V8 models, unbolt the dipstick tube. Remove the spark plug heat shields. Set the parking brake and block the rear wheels. Raise the front of the vehicle and support it securely on jackstands. Disconnect the exhaust crossover pipe from the manifold outlet. Note: Penetrating oil is usually required to remove frozen exhaust pipe nuts. Don't apply excessive force to frozen nuts-you could shear off the exhaust manifold studs. Remove the two front and two rear manifold mounting bolts first, then the center bolts to separate the manifold from the head. Some models use locking tabs under the manifold bolts to keep the bolts from vibrating loose. On these models the tabs will have to be flattened before the bolts can be removed. Installation is basically the reverse of the removal procedure. Clean the manifold and head gasket surfaces to remove old gasket material, then install new gaskets. Do not use any gasket cement or sealer on exhaust system gaskets. Install all the manifold bolts and tighten them to the specified torque. Work from the center out and approach the final torque in three steps. Apply anti-seize compound to the exhaust manifold-to-exhaust pipe studs and use a new exhaust "doughnut" gasket, if equipped.