Replacing the exhaust manifolds on your Ford F-150 truck is a complicated process that varies greatly depending not only on the year of the truck but also the type of engine. The manifolds are connected to the cylinder heads and the catalytic converters. You should talk with your mechanic before attempting this type of repair.
Disconnect the truck's negative battery cable, then raise the truck and securely support it on jack stands.
Disconnect the electrical connectors to the oxygen sensor.
Remove the nuts connecting the exhaust Y-pipe to the manifolds. Apply penetrating oil to the nuts and studs, if necessary.
Remove the engine lifting bracket. For the driver's side manifold, remove the dipstick tube from the oil pan by removing its nut and pulling it out. For the passenger's side manifold, disconnect the EGR pipe from the manifold.
Disconnect the six mounting nuts for the exhaust manifold. Separate the manifold from the cylinder head and remove the old gaskets.
Place the replacement exhaust manifold with new gaskets onto the cylinder head. Install the mounting nuts with a torque wrench, tightening the centre nuts first, followed by the front pair and the rear pair.
Reconnect and install the other components in the reverse order of removal--this can include the engine lifting bracket, oil dipstick tube, EGR pipe and oxygen sensor electrical connector.
Lower the truck and reconnect the battery cable.
Disconnect the negative battery cable, raise the truck and support it on jack stands. Remove the inner splash shield from the bumper well.
Disconnect the EGR pipe at the EGR valve and exhaust manifold if you are removing the driver's side manifold on a 4.6 litre engine. On a 5.4 litre, remove the front and rear heated oxygen sensors and the exhaust support bracket.
Remove the starter if you're removing the passenger's side manifold. Also remove the stabiliser bar on a 5.4 litre engine.
Disconnect the catalytic converter assemblies from the manifold on a 5.4 litre engine by removing their nuts, then move the assemblies to the rear of the truck.
Remove the mounting nuts from the exhaust manifold and remove it. Remove the studs from the cylinder heads and discard them and the nuts.
Clean the mating surface on the cylinder heads, using a gasket scraper to remove any carbon deposits. Install new studs into the cylinder heads.
Place the exhaust manifold over the studs with new gaskets. Install new mounting nuts, working from the rear to the front and alternating between the top and bottom rows.
Install the remaining components in the reverse order of removal and lower the truck. If you need to reconnect the EGR pipe, apply a small amount of anti-seize compound on the threads.
Start the engine after installation and check for leaks in the exhaust system.