Manifold and exhaust system - Td4 (Description): Description and operation

Description

General

The inlet manifold directs cooled compressed air from the turbocharger and intercooler into the cylinders, where it is mixed with fuel from the injectors. Exhaust gases from the exhaust manifold can also be directed into the inlet manifold via a pipe from the exhaust manifold and an Exhaust Gas Recirculation (EGR) valve on the inlet manifold. The exhaust manifold allows combustion gases from the cylinders to leave the engine where they are directed into the turbocharger and exhaust system.

The exhaust system is attached to the turbocharger and is directed along the underside of the vehicle to emit exhaust gases from a tailpipe at the rear of the vehicle. An oxidation catalytic converter is installed midway along the system and a tail silencer is located at the rear of the vehicle.

Inlet Manifold

The inlet manifold is a one piece plastic moulding with inlet tracts feeding intake air into the cylinder head ports directly in the cylinder head and via the camshaft cover. The manifold is secured to the cylinder head using four studs with nuts and one bolt, all incorporating sealing washers and compression limiters.

The manifold is secured to the camshaft cover with eight bolts incorporating compression limiters. Sealing between the manifold, cylinder head and camshaft cover is achieved using moulded rubber seals located in recesses in the manifold.

A boost pressure sensor is located in the right hand end of the inlet manifold. The sensor is secured to the manifold with a bolt and sealed with an 'O' ring. On the left hand end of the manifold, four threaded holes provide for the attachment of the EGR valve. The valve is sealed to the manifold with an 'O' ring.

Exhaust Manifold

The cast iron exhaust manifold is secured to the cylinder head using eight studs with nuts. Two metal gaskets seal the manifold to the cylinder head.

A flanged connection on the underside of the manifold provides for the attachment of the turbocharger. The turbocharger is attached to the flange with three bolts and sealed with a metal gasket.

A second flange, located on the left hand end of the manifold provides the connection point for the EGR pipe. The pipe flange is secured to the manifold with two bolts. There is no gasket used between the EGR pipe and the exhaust manifold.

Exhaust System

The exhaust system comprises three major parts; a front downpipe assembly, an intermediate pipe incorporating a catalytic converter and a tail pipe assembly.

Downpipe Assembly The downpipe assembly is a tubular fabricated and welded construction. The downpipe is attached to the turbocharger by a flange which is secured with two lock nuts. The downpipe connects to an integral flexible pipe which terminates with a flange. The flange connects to the intermediate pipe and is sealed with a metal gasket. The downpipe is supported between the flexible pipe and the lower flange by a welded support bracket and a mounting rubber.

The flexible pipe is formed into a concertina shape with woven metal strands around its outer diameter. The flexible pipe allows for ease of exhaust system alignment and also absorbs engine vibrations. The woven metal strands increase the longevity of the flexible pipe.

Intermediate Pipe Assembly The intermediate pipe has a flange at its forward end with three captive studs which mate with the flange on the downpipe assembly.