Q: How to replace the intake manifold on LY2 and LY6 engines on 2007 GMC Sierra 3500 Classic?
A: To remove ly2 and ly6 intake manifolds, start by removing the air cleaner outlet duct and the generator. Loosen the engine harness retainer and remove the retainer from the stud and locator pin. Remove all the engine harness electrical connectors on the evap canister purge solenoid , manifold absolute pressure (MAP) sensor, ignition coil harness , left side fuel injectors , throttle actuator, right side fuel injectors, engine coolant temperature (ECT) sensor. Throttle back the engine harness branches to the cowl panel, then reposition the Brake Booster Vacuum Hose clamp and pull the vacuum hose from the booster fitting. Unplug the evap canister purge tubes and feed line and the positive crankcase ventilation (PCV) hoses from the Intake Manifold. Remove the Intake Manifold boltheads (512) and detach the Intake Manifold (500), covering the cylinders head ports to avoid debris entry. Remove the Intake Manifold gaskets (514) and if replacing the manifold be sure to remove the Brake Booster Vacuum Hose from Intake Manifold nipple, upper Intake Manifold cover nut, and the cover itself. Take out the MAP Sensor retainer and the MAP Sensor, and disconnect the evap tube quick connect fitting and free the retainer for the evap canister purge solenoid. Remove Throttle Body and its gasket, and then detach Fuel Rail evenly to remove it and dump Fuel Injector lower o-ring seals. When installing, connect the Brake Booster Vacuum Hose nipple to a new Intake Manifold, fit new Fuel Injector lower o-ring seals then inject clean engine oil and install the Fuel Rail and tighten the bolts to 10n.m (89 lb in). Mount a new Throttle Body Gasket onto the Intake Manifold, install the Throttle Body, and fasten it in using bolts/nuts (tightened to 10 N.m (89 lb in)). Note: connect the evap tube quick connect fitting, lubricate the seal to the MAP Sensor, and the MAP Sensor and the retainer. Install the upper Intake Manifold cover and nut and tighten until tight, reattach the Brake Booster Vacuum Hose and clamps. Replace new Intake Manifold gaskets (514) and the Intake Manifold (500), tightening the bolts (512) with 5 n.m (44 lb in) and 10n.m (89 lb in), respectively, in the series. Re-attach the pcv hose , fuel feed line , and evap canister purge tube , then connect the Brake Booster Vacuum Hose to the booster connection. Unfasten the engine harness branches, reconnect the ect sensor, and secure one end of engine harness clip to generator bracket and tighten the bolt to 9 n.m (80 lb in). Lastly, connect the electrical connectors to the right and left side fuel injectors, throttle actuator, ignition coil harness, map sensor, and evap canister purging solenoid, install the engine harness retainer and nut tightened to 5 n.m (44 lb in), and re-install the generator and air cleaner outlet duct.