Repair 7

DIY Intake Manifold

A vehicles intake manifold distributes the mixture of fuel and air to the engine cylinders. If the intake manifold is cracked or the mating surfaces are warped, this will cause the fuel/air to leak and the manifold must be replaced. The following instructions are general for removing and installing the manifold. The exact procedure can vary with each model, however, especially regarding the exact wires and lines connected to the manifold. It is very important that you have a manual written specifically for your model vehicle.

Removal

Because you are working on the fuel system, you need to depressurize the system. Remove the fuel pump relay from the fuse box and then start the engine until it stalls. You are also working with electrical connectors, so disconnect the negative cable from the battery. The manifold is also connected to the cooling system, so you must either drain the coolant or clamp off the coolant hose to the manifold before disconnecting it. Once all these precautions are done, disconnect all electrical connectors and lines attached to the manifold. This can include hoses from the radiator and air duct, the fuel lines, fuel rail and the fuel pressure regulators vacuum hoses, along with the electrical connectors to the crankshaft and camshaft position sensors, A/C compressor, alternator and starter. Now remove the nuts and/or bolts securing the manifold--use a torque wrench and make 1/4-turns until you can remove the bolts by hand. Remove the intake manifold.

Installation

Remove all traces of the gasket/sealant material from the engine cylinder heads with a gasket scraper, and make sure there is none on the manifolds surfaces as well. Clean those surfaces with acetone or lacquer thinner. If any material falls into the cylinder head intake ports, remove it with a vacuum cleaner. Clean up the bolts (or the manifolds studs) and apply a thin coat of engine oil to the threads. Apply a new gasket or RTV sealant to the manifolds mating surface. Make sure the intake ports, coolant holes and bolt holes are all properly aligned as you install the manifold in place and tighten the nuts/bolts. Now reconnect all the hoses, lines and electrical connectors to the manifold. Once everything is connected, you can unclamp the coolant hoses and reconnect the battery cable and fuel pump relay. Re-pressurize the fuel system by repeatedly turning on the engine for two seconds and then leaving it off for five. Start up the engine and see if oil or coolant leaks at the manifolds joints.