Exhaust system
1 The exhaust system consists of front, intermediate and rear sections, the number varying according to model. The system is suspended from the underbody on rubber mountings, and bolted to the exhaust manifold at the front. Flanged joints incorporating gasket seals or pipe clamps are used to secure the sections. The front section downpipe is of twin, or “siamesed” type and is attached to the manifold by a flanged joint incorporating compression springs or by a single spherical joint. On TU series engines, a ball-and-socket type joint is provided between the front downpipe and intermediate pipes, to allow for engine movement.

2 Later fuel-injected models are equipped with a catalytic converter as part of the exhaust emission control system.

Emission control systems 3 Various systems may be fitted to reduce the emission of unburned hydrocarbons and harmful exhaust gases into the atmosphere.

Basically, these systems can be divided as follows:
a) Air inlet heating system.

b) Crankcase ventilation system.

c) Electro-pneumatic ignition timing retarding system.

d) Catalytic converter.

e) Fuel vapour recirculation system.

4 The operation of the systems is described briefly in the following paragraphs.

Air inlet heating system 5 This system is fitted to certain carburettor and all single-point fuel injection models, and assists the vaporisation of the fuel, providing more complete combustion of the fuel/air mixture (see illustration). This is achieved by controlling the temperature of the air entering the engine.

1.5 Typical air intake heating system

1 Air cleaner
2 Air ducting
3 Exhaust manifold
hot air duct
4 Flap valve
5 Wax thermostat
a Cold air
b Hot air

6 The air drawn through the air inlet pipe from the engine compartment is mixed with hot air drawn from a shroud around the exhaust manifold. The proportions of hot and cold air are controlled by the position of a flap valve, which in turn is controlled by a wax thermostat and a vacuum capsule (connected to the inlet manifold).

Crankcase ventilation system 7 This system is fitted to all models, and prevents the gases produced in the crankcase from being released into the atmosphere, at the same time preventing a build-up of pressure in the crankcase (see illustration).

1.7 Typical crankcase ventilation system

1 Oil filler cap with oil trap 2 Air filter
3 Throttle valve
4 Inlet manifold
5 Jet
6 Ventilation hose
7 Calibrated jet
8 Sump
9 Camshaft cover

8 Crankcase gases are drawn into the air inlet tract, where they are mixed with clean air. The gases are then burnt with the fuel/air mixture in the engine, and expelled through the exhaust.

Electro-pneumatic ignition timing retarding system
9 This system is used on models fitted with the Mono-Jetronic A2.2 fuel injection system, and reduces the nitrous oxide (NOx) content in the exhaust gases (see illustration).

1.9 Electro-pneumatic ignition timing retarding system

1 Coolant temperature sensor 2 Electronic control unit 3 Solenoid valve
4 Distributor vacuum capsule

This is achieved by reducing the temperature at the end of the combustion by reducing the ignition advance at certain engine temperatures.

10 The engine temperature is measured by a coolant temperature sensor, and this information is transmitted to the electronic control unit, which controls the solenoid valve.

Under certain engine temperature conditions, the solenoid valve cuts off the vacuum to the distributor vacuum capsule, therefore reducing the ignition advance.

Catalytic converter
11 Catalytic converters have been introduced progressively on all models in the range, to meet emissions regulations.

12 The catalytic converter is located in the exhaust system, and operates in conjunction with an exhaust gas oxygen sensor to reduce exhaust gas emissions. The catalytic converter effectively cleans the exhaust gases by speeding up their decomposition.

13 In order for a catalytic converter to operate effectively, the air/fuel mixture must be very accurately controlled, and this is achieved by measuring the oxygen content of the exhaust gas. The oxygen sensor transmits information on the exhaust gas oxygen content to the electronic control unit, which adjusts the air/fuel mixture strength accordingly.

Fuel vapour recirculation system 14 This system has been introduced progressively on all fuel injection models, and prevents fuel vapour from the fuel tank from being ejected into the atmosphere (see illustration).

1.14 Fuel vapour recirculation system

1 Fuel filler cap
2 Charcoal canister
3 Hose
4 Calibrated orifice
5 Hose
6 Solenoid valve
7 Coolant temperature sensor 10 Safety valve

15 The fuel filler cap is sealed, and the fuel vapours from the tank pass into a carbon canister, via a calibrated orifice and a pipe.

The fuel vapour is absorbed by the carbon filling in the canister.

16 When the engine is running, it draws a proportion of its inlet air through the carbon canister, and this air picks up the fuel vapour contained in the carbon canister.

17 A solenoid valve mounted in the pipe between the canister and the inlet manifold prevents the system from operating when the engine is cold. The solenoid valve is controlled by the electronic control unit, on the basis of information received from the coolant temperature sensor.