GMC 12611155 Manifold, Lower Intake (Machine)

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To remove the intake manifold covers, first disengage the locking tab on the oil filler spout with a small screwdriver and rotate it counterclockwise to remove. Next, disconnect the brake booster vacuum hose and vacuum lines from the fittings, followed by the electrical connectors for the Camshaft Position (CMP) sensor and the left knock sensor. Remove the power steering fluid reservoir mounting bracket fasteners and set the reservoir and bracket aside. Disconnect the electrical connector and vacuum hose from the switching valve at the rear of the plenum, then lift and remove the intake manifold cover, with installation being the reverse of removal. For the right side, relieve the fuel system pressure, disconnect and remove the fuel lines to the fuel rail, and disconnect the quick-disconnect fitting to the EVAP hose. Disconnect the wiring harness fasteners mounting the harness to the Engine Control Module (ECM) bracket, disconnect the cable from the negative battery terminal, and remove the after run coolant pump-to-ECM mounting bracket fasteners, setting the pump aside. Disconnect and remove the ECM, then remove the ECM bracket mounting fasteners from the intake plenum and cylinder head before lifting and removing the intake manifold cover, with installation being the reverse of removal. For the upper intake manifold, first remove the intake manifold covers if equipped, relieve the fuel system pressure, disconnect the cable from the negative battery terminal, and remove the intake plenum. Disconnect and remove the fuel lines to the fuel rail, disconnect the quick-disconnect fitting to the EVAP hose, disconnect the fuel injector's electrical connectors from the main engine harness, and disconnect the vent tube from the fuel pressure regulator. If replacing the upper intake manifold, remove the fuel rail from the manifold. The intake manifold is secured with six bolts along its base; remove these bolts and pull the intake manifold and fuel rail away from the engine. When installing, use new manifold gaskets and tighten the bolts in several stages, working from the center out to the specified torque, with installation otherwise being the reverse of removal. For the lower intake manifold, first remove the upper intake manifold, then remove the lower intake manifold-to-cylinder head bolts and take the manifold off the cylinder heads. For installation, use new manifold gaskets and tighten the bolts in several stages, working from the center out to the specified torque, with installation otherwise being the reverse of removal.

To remove the intake manifold, the following must be done; disconnect the cable from the negative terminal on the battery and then release the fuel pressure. Further, un-bolt the air intake duct and, take off electrical connector of the throttle body along with the connectors of fuel injectors, EVAP purge solenoid and MAP sensor. Aside from the removed wiring harness connections, there are more brackets which should be detached from the upper part of the intake manifold and the wiring harness should be set aside. As a general procedure it is good that the fuel rails and injectors can be pulled out together so that there is no harm done to what is being worked on in this case the intake manifold. Remove all vacuum hoses that are connected on manifold or throttle body, then ease off the intake manifold bolts in reverse order of the lightening sequence in crawl-allity or a quarter turn till they are easy to remove fully. If the manifold is seized, use of a prybar can be gently used to separate the gasket surfaces thus releasing the gasket from its sealed position without damaging the sealing areas. After the manifold has been detached make sure that the mating surfaces in the cylinder head, block and the manifold are clean. Clean away all remains of the old gasket materiel carefully in a manner that does not harm the surfaces, and use safety solvent to wet a cloth. Hit on the threads with a tap to push the coarse threads into the holes further then use compressed air to blow out dirt. Align the new gaskets to the intake manifold so that they click into their appropriate position. Gently position the manifold and using medium strength locking compound; fit the bolts and tighten them strictly in the sequence to a certain torque value but not beyond the recommended torque. Last but not the least, do the installation in the very style it was pulled apart, start the engine and look for vacuum leaks particularly round the intake manifold joints.

The remainder of the installation follows the reverse order of removal, checking the coolant level and starting the engine to check for vacuum leaks at the intake manifold joints.

For these models, disconnect the PCV tube and EVAP hose, remove the fuel rail shield, and disconnect any electrical connectors before lifting off the intake manifold and gasket.

Apply medium-strength thread locking compound to the bolt threads, install and tighten the bolts in the correct sequence, and complete the installation in reverse order of removal.

Proceed to remove the intake manifold insulator fasteners and insulator, followed by the intake manifold mounting fasteners, noting the locations of the stud bolts, and finally remove the intake manifold from the cylinder head.

Lift the old gaskets off, use a gasket scraper to remove all traces of sealant and old gasket material, and clean the mating surfaces with brake system cleaner.

Loosen the six mounting bolts from the upper intake manifold but do not remove them, then remove the manifold and gasket as a unit, discarding the gasket afterward.

Start by removing the engine cover and the air outlet tube from the air filter housing, then move the PCV tube from the air filter inlet. Disconnect the electrical connectors to the intake manifold tuning valve, throttle body, and MAP sensor, as well as the brake booster vacuum hose and wiring from the throttle body.

Remove the alternator bracket into which the mounting bolt was threaded, loosening the upper alternator mounting bolt and sliding it out far enough to remove this bracket.

The remainder of the installation follows the reverse order of removal. Finally, reconnect the battery and run the engine to check for vacuum and fuel leaks.