Automotive mechanics (volume i)(part 2, chapter15) intake and exhaust systems

213-246_May_chap 15

12/9/06

10:07 AM

Page 231

231

Chapter 15

Intake and exhaust systems

Air cleaners
Carburettor air cleaners
EFI air cleaners
Diesel air cleaners
Air-cleaner service
Engine manifolds
Intake-system problems
Exhaust systems
Exhaust-system service
Exhaust-system problems
Technical terms
Review questions


213-246_May_chap 15

12/9/06

10:07 AM

Page 232

232 part two engines and engine systems
The intake system is responsible for providing clean
air and carrying it into the cylinders of the engine. The
system includes the air cleaner and the intake manifold
and other ducting and passages. In petrol engines, the
air from the intake system carries the air–fuel mixture
into the cylinders. In diesel engines, the intake system
carries only air.
The exhaust system carries the exhaust gases away
from the engine and reduces the exhaust noise. It
consists of the exhaust manifold, exhaust pipes, and
one or more mufflers. Most petrol engines also have a
catalytic converter to reduce the exhaust emissions.
■ This chapter covers normal intake and exhaust
systems. Induction systems and turbochargers are
covered in Volume 2.

Air cleaners
An air cleaner has a filter element through which all
the air passes before it enters the engine. The air
cleaner body also acts as a silencing chamber to muffle
the sound of the incoming air.
A considerable amount of air passes through the
intake system into the engine. By mass, it is about
fifteen times the amount of fuel. The air must be

filtered because, even under good conditions, dust and
grit are present in the air.
If unfiltered air is allowed to enter the engine, it
will act as an abrasive and cause premature wear to the
valve guides, piston rings, pistons and cylinder walls.

figure 15.1

On a carburettor engine, the air cleaner is
usually mounted on top of the carburettor

Dry-element air cleaners
This type of air cleaner (Figure 15.2) contains a
replaceable element, which is made from pleated paper
or cellulose fibre. This is a very fine porous material. It
is fine enough to filter the impurities from the air, but
porous enough to allow the clean air to pass through
with very little restriction.
The air cleaner body is made of pressed steel. The
top of the filter can be removed to access the
replaceable filter element.

Types of air cleaners
There are a number of different types of air cleaners, all
of which contain some type of filtering element to
remove dust from the air. Air cleaners for passenger
and light commercial vehicles have a dry filter element,
but air cleaners with wet elements have been used.
These have a filtering element that is wet with oil.
There are different arrangements of the filtering

systems for carburettor engines, EFI engines and diesel
engines.

Carburettor air cleaners
Most carburettor engines have a large circular air
cleaner like the one shown in Figure 15.1. This is
located on top of the carburettor. Apart from its
filtering action, the filter of a carburettor engine can
act as a flame trap. If there is an engine backfire, the
filter will contain the flame within the air cleaner.

figure 15.2

Dry-type carburettor air cleaner cut away to
show the filter element FORD

Hot-air controls in air cleaners
On carburettor engines, a shroud fitted around the
exhaust manifold provides heated air, which can be
taken into the air cleaner through a connecting pipe.
The air cleaner has a flap valve in its air inlet,
which automatically controls the amount of heated air
that enters the air cleaner. The flap (or control valve)
in some air cleaners is operated by a thermostatic
spring, in others, by a vacuum control.


213-246_May_chap 15

12/9/06

10:07 AM

Page 233

chapter fifteen intake and exhaust systems

233

The heated air provides better vaporisation of the
fuel under cold conditions. It also reduces the amount
of unburnt hydrocarbons that are emitted through the
exhaust.
Thermostatic control
This arrangement is shown in Figure 15.3. When the
engine is first started the flap valve is fully open to
allow only heated air to the air cleaner. As the engine
operating temperature increases, the thermostatically
controlled flap valve gradually closes off the hot air
passage and opens the normal air intake.
A mixture of heated air and cool air (air at
atmospheric temperature) is provided until the engine
warms up. With the engine warm, the flap valve will
have closed off the hot air passage and fully opened
the air intake.

figure 15.4

Vacuum operated hot-air control on an air
cleaner MITSUBISHI

At intermediate temperatures, the flap valve will be
partly open and air entering the air cleaner will be a
mixture of cool air and hot air, being regulated by the
thermosensor valve.
Wet-type air cleaners
There are two types of wet air cleaners: oil-wetted and
oil bath.
Oil-wetted air cleaner

figure 15.3

Arrangement for heated air to a carburettor
air cleaner
1 air cleaner, 2 flap valve, 3 cool air, 4 thermostatic control,
5 hot air from around the exhaust manifold MAZDA

Vacuum control
A vacuum control unit is shown in Figure 15.4. This
has a diaphragm with a rod attached to a control valve
(flap valve). The chamber above the diaphragm is
connected by a tube to the intake manifold.
When the engine is started, intake manifold vacuum
(negative pressure) applied to the diaphragm opens the
control valve and allows hot air into the air cleaner.
A thermosensor valve, located inside the air
cleaner, senses changes in the air temperature. When
this is less than 30°C, the thermosensor valve is open.
This allows vacuum to reach the diaphragm and open
the control valve to supply hot air.

When the air temperature rises to 45°C, the thermosensor valve cuts off the vacuum. The spring pushes
the diaphragm down and the control valve closes off
the hot air.

An oil-wetted air cleaner has an element made of metal
strands packed closely together. These are wet with oil.
The air moving through the air cleaner passes through
the element where particles of dust are collected on the
oily strands.
Oil-bath air cleaner
This type of air cleaner uses a similar element to an
oil-wetted type but, in addition, has a bath of oil in the
bottom of the cleaner. Air entering the cleaner passes
across the surface of the oil, which collects the
particles of dust (Figure 15.5).
The air passing through the cleaner suddenly
changes its direction as it reaches the oil. The dust
particles do not change direction, but continue on into

figure 15.5

Principle of an oil-bath air cleaner


213-246_May_chap 15

12/9/06

10:07 AM

Page 234

234 part two engines and engine systems
the bath of oil. The dust is trapped in the oil and sinks
to the bottom of the container.
The air is further filtered through an oil-wet filter
element before entering the engine.
■ Oil-wetted or oil-bath air cleaners are only likely to
be found on older vehicles or in special applications.

EFI air cleaners
Multipoint electronic fuel injection (EFI) systems
usually have the air cleaner located at the side of the
engine and connected into the intake system by large
hoses and ducts.
Air cleaners used with EFI can be rectangular or
round. Apart from their shape and location, the filter
elements are similar to air cleaners for carburettor
engines.
The EFI air cleaner in Figure 15.6 has a plastic
body. The flat rectangular filter is made of cellulose
fibre and this is supported in the air-cleaner body and
enclosed by a cover. The air cleaner is mounted beside
the engine. It is located in the air-intake system, ahead
of the airflow sensor and throttle body.
Air enters through the air intake at the side of the
air cleaner body and passes upwards through the filter
element.

■ Engines with throttle-body EFI have the air filter

mounted on top of the throttle body assembly and
are similar to carburettor air cleaners.

EFI air-cleaner and ducts
Figure 15.7 shows the components of an EFI aircleaner assembly with its hoses and ducting. The air
intake is made of moulded plastic material and located
at the front of the engine compartment. The intake
shown has an air chamber that can hold a volume of
air. This acts as a resonator to reduce the noise of the
incoming air.
The system shown also has a supplementary
resonator fitted after the air cleaner. This helps to
reduce air pulsation.
Figure 15.8 shows the air cleaner and air ducts for a
different EFI system. This carries air from the front of
the vehicle to the throttle body on the intake manifold
of the engine.
Figure 15.8(a) shows the parts of the system. The
air cleaner is bolted to the body beside the engine.
There is a long duct between the air cleaner and the
front of the car for air intake, and a flexible hose
between the air cleaner and the throttle body.
Figure 15.8(b) shows the dismantled air cleaner
assembly. This has an air filter element and also a
noise-reduction filter. The airflow sensor for the EFI
system is attached to the air cleaner cover. When the
cover is assembled to the body, the airflow sensor
fits inside the filter element. An electrical connector
on the sensor connects it to the electronic control
unit.

■ With EFI systems, it is essential that there are no
air leaks. All the air entering the engine is
accurately measured by the airflow sensor. An air
leak at a connection after the sensor would upset
the air–fuel mixture.
EFI intake system

figure 15.6

Air cleaner for an EFI system

Figure 15.9 shows the intake system for a fourcylinder engine. The air is taken in through the air
intake at the front of the engine. It passes through the
air cleaner, the airflow sensor and the throttle body to
the plenum chamber. This acts as a form of air
reservoir. Air is then carried through the intake
manifold to the cylinders of the engine.


213-246_May_chap 15

12/9/06

10:07 AM

Page 235

chapter fifteen intake and exhaust systems
cover
air intake hose

filter
air cleaner body

resonator

clip
air intake

figure 15.7

Air cleaner and ducting for an EFI engine

figure 15.8

Air intake system for an engine with EFI

HYUNDAI

HYUNDAI

235


213-246_May_chap 15

12/9/06

10:07 AM

Page 236

236 part two engines and engine systems
plenum chamber

mounting
bracket

throttle body

cover
filter
element

air
cleaner
body

air intake

baffle

body

intake manifold

vanes

dust
bowl

clamp
bolt

air ducting

figure 15.9

figure 15.11

Cyclone-type air cleaner

Air intake system and intake manifold for a
four-cylinder EFI engine TOYOTA

Diesel air cleaners
Diesel engines often have more than one air cleaner
and these are often mounted away from the intake
manifold. They have ducting which connects them to
the engine (Figure 15.10). Off-road vehicles are likely
to have a precleaner and a main cleaner.
The air intake of some off-road vehicles is mounted
externally and raised almost to the height of the
passenger cabin. This keeps the air intake above the
dust created by the vehicle.

The cyclone filter is so named because of the
swirling action of the air as it passes through the air
cleaner. To create this airflow, vanes are fitted inside
the body of the air cleaner.
The air cleaner operates in the following way: Air

entering the air cleaner passes over the angled vanes
and these impart a rotary motion to the airflow. This
spins out the heavier particles of dust, which are
collected in the bowl at the bottom of the cleaner.
The air then passes through a dry-filter element for
further cleaning before passing on to the intake
manifold.
■ The cyclone filter and a dry air filter are combined
in the filter shown, but cyclone filters are also made
as separate air cleaners.

Air-cleaner service

figure 15.10

Air cleaner of the type used for diesel
engines

Cyclone-type air cleaners
A cyclone-type air cleaner is shown in Figure 15.11.
The cyclone filtering arrangement is not efficient
enough on its own, and so it is used as a precleaner for
a dry-type filter.

Filter elements should be removed for service at
periods recommended by the manufacturer. However,
if the vehicle is operating in unusually dusty
conditions, the air cleaner must be serviced more
frequently.
Servicing the element varies according to its type,

as indicated below.
■ The main purpose of the air cleaner is to keep
damaging dust from entering the engine. If the
element becomes clogged, is damaged, or does not
fit properly, it will not do its job and the engine will
suffer.


213-246_May_chap 15

12/9/06

10:07 AM

Page 237

chapter fifteen intake and exhaust systems

Dry-element cleaners
The element can be removed for cleaning and
examined against a light for punctures. Paper-type
elements should not be washed in any type of cleaning
solution, as this will destroy the filtering effect.
There are two methods of cleaning:
1. The element can be carefully and lightly tapped on
a clean flat surface to dislodge the dust particles.
The element must be kept flat as this is being done.
Do not strike the element on its edge, or in such a
way that it will become distorted or damaged and
so fail to seal when reinstalled.

2. The element can be cleaned by blowing with air
(Figure 15.12).
With a flat filter, air is blown from the inside
to the outside, that is, in the opposite direction to
normal air flow.
With a round filter, air is carefully blown from
the centre of the element outwards to dislodge dust
from the outer surface of the filter paper.
■ Care must be taken not to blow holes in the paper,
so the nozzle of the air gun must be held at least
100 mm away from the inside of the element.

237

a matching groove and tab. Failure to match these
during reassembly can distort the cover and cause air
leaks.
Where the cover of the air cleaner is secured by a
wing nut, it should not be overtightened because this
can also cause distortion.
Oil-wetted and oil-bath cleaners
The element of an oil-wetted filter is serviced by
immersing it in cleaning solvent and agitating it to
remove the oil and dirt.
After draining, and blowing with air, the element is
re-oiled with engine oil. It is then allowed to stand so
that surplus oil will drain off before it is reinstalled.
The filter element of an oil-bath air cleaner is
removed and serviced in a similar way to an oil-wetted
type. The oil in the cleaner body is discarded and the

body is washed to remove dust deposits. It is then
filled to the level mark with engine oil.
■ Avoid overfilling, as this can have a restricting
effect on the air flow and cause loss of engine
power.
Cyclone cleaner service

inside
outside

figure 15.12

The air-cleaner element can be blown lightly
to remove dust MAZDA

This type of air cleaner is serviced by removing the
dust bowl from the bottom and cleaning out the dust.
The inside of the body can be wiped out with a
damp cloth. When operating in dusty conditions, the
bowl should be removed and cleaned frequently to
prevent it from becoming overloaded. If this occurs,
the filter element of the main filter will be doing all the
filtering and could become clogged.
If the cyclone air cleaner also has a filter element,
this can be removed and cleaned in the same way as
other dry-type elements.

Renewing the filter element
While the filter element can be cleaned, the pores of
the filtering material will gradually become blocked.

This will restrict air flow and so manufacturers specify
that the filter element should be renewed after a certain
period. For example, every 30 000 km of operation, or
more often if the vehicle is used in dusty conditions.
When reassembling the element to the air cleaner,
make sure that it fits and seals correctly. Sealing is
important to prevent unfiltered air from entering the
system.
On some carburettor air cleaners, the body and the
cover are located in relation to each other by means of

EFI air-cleaner service
With EFI filters, clips are used to secure the cover to
the body. Releasing the clips enables the cover to be
separated from the body. The filter element can then
be removed.
The element is cleaned in the same manner as other
dry-type elements. If electrical connections have to be
disconnected to access the filter, this should be done
carefully.
The ducts and hoses should be checked to make
sure that the connections are tight and that the joints do
not have air leaks.


213-246_May_chap 15

12/9/06

10:07 AM

Page 238

238 part two engines and engine systems

Engine manifolds

Carburettor engine manifolds

There are basic differences between the manifolds
used on carburettor engines, EFI engines and diesel
engines. This applies particularly to intake manifolds.
Some of their features are:

Figure 15.13 shows a typical cylinder head and its
intake and exhaust manifolds. This is for a fourcylinder carburettor engine. It is a crossflow cylinder
head, with the intake manifold on one side and the
exhaust manifold on the other.
The intake manifold has a mounting for the
carburettor and a flange which bolts onto the cylinder
head. It has four branches that carry the air–fuel
mixture from the carburettor to the cylinders. The
manifold is made from aluminium alloy for reduced
weight and good heat transfer.
Most carburettor intake manifolds are heated to
improve the vaporisation of the air–fuel mixture when
the engine is cold. The manifold shown has a waterjacket under the carburettor mounting. This is supplied
with a flow of engine coolant.

1. Carburettor engines have intake manifolds that

carry a mixture of air and fuel into the engine.
2. EFI engines with throttle-body injection have
intake manifolds that are similar to carburettor
manifolds. They also carry a mixture of fuel and air
into the engine.
3. EFI engines with multipoint injection have intake
manifolds that carry air. Injectors in the manifold
spray fuel into the intake ports of the cylinder
head.
4. Diesel engines have manifolds that carry air only.
The fuel is injected directly into the cylinder.

figure 15.13

Cylinder head and manifolds for a carburettor engine

HOLDEN LTD


213-246_May_chap 15

12/9/06

10:07 AM

Page 239

chapter fifteen intake and exhaust systems

239

EFI engine intake manifolds
An inlet manifold for an EFI engine is shown in
Figure 15.14. This is made of aluminium alloy. It has
long branches and a plenum chamber. The plenum
chamber provides a surge chamber which reduces
intake air resistance.
The branches of the manifold are designed to be of
equal length. The long branches create an inertiacharging effect that improves intake efficiency.

cover

plenum chamber

upper
intake manifold
air inlet

fuel rails
and injectors

seal

figure 15.14

Intake manifold for an EFI engine – arrows
show the air flow HYUNDAI
lower intake
manifold

V-type engine intake manifolds
V-type engines have the intake manifold located in the
valley between the two cylinder heads. Branches of
the manifold go to the intake ports at each side.
Figure 15.15 shows the parts of an intake manifold
assembly for a V-6 engine. The lower intake manifold
fits between the cylinder heads and the upper intake
manifold is bolted to it. The cover is then bolted to the
upper intake manifold to form the plenum chamber (air
chamber).
Seals are used between the parts so that the
assembly is airtight. The injectors fit into holes in
the lower intake manifold. They are attached to the
fuel rails, which supply them with fuel.
Variable intake manifold
With EFI engines, the branches of an intake manifold
(also called runners) are designed to have a particular
length and diameter to suit the engine. The design is
something of a compromise, because the requirements
of an intake manifold at high engine speeds are
different to those at low speeds.
At low engine speeds, the branches of the intake
manifold need to be of small diameter so that the

figure 15.15

Parts of an intake manifold assembly for a
V-type engine – the fuel rails and injectors
are also shown HOLDEN LTD

velocity of air is maintained. At high engine speeds,
the branches need to be larger in diameter so that the
air flow is not restricted.
There is also the pulsation of the air in the manifold
to be considered. A ram air effect can be created in the
manifold if it is tuned to the right length. The ram
effect originates with piston and valve action, which
produces pulsations in the manifold. The pulsations
can be accentuated by the design of the manifold and
used to produce the ram effect.
Dual branches or runners
To provide for the different requirements at high and
low engine speeds, intake manifolds can be designed
with dual branches as shown in Figure 15.16. The


213-246_May_chap 15

12/9/06

10:07 AM

Page 240

240 part two engines and engine systems
throttle body

control valves
plenum

cylinder head
valve
closed

(a)

throttle body

lever

valve plate
intake port

figure 15.17

Lower part of an intake manifold with dual
branches and control valves FORD

valve
open

(b)

figure 15.16

Intake manifold with dual branches (runners)
(a) air flow at low engine speeds (b) air flow at
high engine speeds FORD

diagrams show a cross section of one branch. There are

two paths that the air can take, a long path and a short
path. These are controlled by throttle-type valves.
At low speeds, the valve plate is closed as shown in
Figure 15.16(a) and the air is directed around the
longer and narrower path to the engine.
At high speeds, the valve plate is opened as shown in
Figure 15.16(b). Most of the air then passes through the
valve and takes the shorter and wider path to the engine.
The valves are located between the plenum
chamber and the manifold branches (Figure 15.17).
There is a valve plate for each branch and these are
mounted on a common shaft that is rotated by a
vacuum control unit. This, in turn, is controlled by the
engine’s power control module.

Intake-system problems
Some problems for EFI and carburettor engine airintake systems and the likely effects are:
1. Restricted filter. A blocked filter element in the air
cleaner could restrict air flow and cause loss of
engine power, particularly at higher speeds.
2. Air leaks, EFI system. An air leak after the air filter
and ahead of the throttle body will admit unfiltered
air into the system.

An air leak after the throttle body will upset the
fuel mixture, because the air will be additional to
that measured by the airflow sensor.
3. Air leaks, carburettor system. An air leak between
the air cleaner and the carburettor will allow
unfiltered air into the system.

Air leaking into the system between the
carburettor and the intake manifold will weaken the
air–fuel mixture.

Exhaust systems
Exhaust manifolds are usually made of cast iron,
which is able to resist the high exhaust temperatures.
Exhaust manifolds can also be fabricated from
stainless steel, which is lighter than cast iron.
The exhaust manifold in Figure 15.13 is made of
cast iron and has four branches, one for each exhaust
port. The branches carry the exhaust gases from the
exhaust ports, and join together to form the exhaust
flange. The manifold flange provides a connection for
the exhaust pipe.
The exhaust manifold is covered by a shroud. This
shields other parts of the engine assembly from the
heat that radiates from the manifold. On carburettor
engines, it also provides a ‘stove’ from which the air
cleaner can receive heated air.
Parts of exhaust systems
An exhaust system for a V-type engine is shown in
Figure 15.18. With a V-type engine, there is an exhaust
manifold on each side of the engine, so dual components are used. There are two catalytic converters


213-246_May_chap 15

12/9/06

10:07 AM

Page 241

chapter fifteen intake and exhaust systems

241

catalytic converters
rear muffler
intermediate
mufflers

flange joints

oxygen sensors

figure 15.18

Exhaust system for a V-type engine

HOLDEN LTD

and two intermediate mufflers, but only one rear
muffler. Some engines have a dual system, with
separate components and pipes for each side.
The engine pipe is attached to the exhaust manifold
outlet by the exhaust flange. Brackets and mountings
on the various parts support the system in relation to
the engine and the body of the vehicle.

Exhaust systems have flexible mountings that allow
for engine movement and also prevent exhaust vibrations
from being transmitted to the body of the vehicle. This
also allows for thermal expansion of the system.
System arrangements
Exhaust pipes are designed with various shapes to suit
the location of the engine and the type and design of

figure 15.19

Components of an exhaust system

HOLDEN LTD

the bodywork of the particular vehicle. Examples of
exhaust installations can be seen in Figures 15.19 and
15.27, although there are many variations of these
arrangements.
The system in Figure 15.19 is for a four-cylinder
transverse engine. It has an exhaust manifold with
separate branches joined to a flange. The pipes joining
the components are identified, from front to rear as: the
engine pipe, or front pipe, the intermediate pipes, the
rear pipe, and the tail pipe.
Twin engine pipes are used between the manifold
and the engine pipe. These are shaped to pass under
the engine.
It has a catalytic converter and two mufflers, one in
the middle and the other at the rear end of the system.

213-246_May_chap 15

12/9/06

10:07 AM

Page 242

242 part two engines and engine systems
Some exhaust systems are designed with extractor
pipes. These have one pipe for each exhaust port. The
pipes are designed with long sweeps that prevent
back pressure. They also provide a scavenging effect,
which assists in extracting the exhaust gases from the
cylinders, thereby increasing engine performance.
The engine pipes in Figure 15.19 have this to some
extent.
Exhaust system connections
The parts of exhaust systems are joined together in
different ways. Exhaust pipes and mufflers can be
joined by fitting the end of one pipe into another
(Figure 15.20). A clamp is then used to hold the parts
firmly together.
Other connections are made with flanged joints.
Figure 15.21 shows a joint between the exhaust flange
of the manifold and a flange on the exhaust pipes. This
has two engine pipes and the exhaust gas from half the
engine’s cylinders is fed into each engine pipe.
A gasket of heat-resistant material is fitted between the

two flanges.

Flexible pipe connections
With transverse engines in particular, semiflexible
connections are used between the manifold and the
exhaust pipe, or as a connection between pipes. This
compensates for movement of the engine in relation to
the body.
Figure 15.22 shows one type of connection. This is
a semiflexible design that assists with alignment of the
pipes and also helps to reduce vibration. In this joint,
the sealing ring between the two pipes has a spherical
end, which fits into a similarly shaped end of the
exhaust pipe. The two bolts that hold the flanges of
the pipes together are fitted with springs so that the
sealing ring is held firmly onto its seat. This provides a
joint that is firm, but not rigid.
Another arrangement of flexible exhaust connection
is shown in Figure 15.23. A section of flexible, metalbraided pipe is inserted in the front exhaust pipe. This

figure 15.22

figure 15.20

Clamping arrangement for an exhaust
muffler

Semiflexible connection in exhaust system
1 mounting-bracket assembly, 2 flange on
engine pipe, 3 sealing ring, 4 conical seat, 5 flange on

intermediate pipe, 6 spring, 7 flange bolt

gasket

oxygen sensor

dual pipes

figure 15.23
figure 15.21

Exhaust manifold to engine pipe connection

flexible
connection

Exhaust pipe with a braided-metal flexible
connection


213-246_May_chap 15

12/9/06

10:07 AM

Page 243

chapter fifteen intake and exhaust systems

243

provides a flexible connection between the parts of the
exhaust system that are attached to the engine, and
the parts that are mounted to the bodywork.
Exhaust mufflers
Mufflers are also referred to as resonators and
silencers, although the term muffler is usually used.
They are designed in various shapes and sizes.
A muffler contains perforated pipes, baffles and
resonance chambers, which are designed to break up
the pulsating effect of the exhaust gases and so reduce
the noise. At the same time, this must be done with as
little restriction as possible, because restrictions cause
back pressure and inhibit gas flow.
Many mufflers have a combination of baffles and
pipes which are perforated so that the pattern of the gas
flow is altered, but not restricted.
The construction of one type of muffler is shown in
Figure 15.24. This is a reverse-flow muffler, where the
direction of flow of the exhaust gases is changed
within the muffler. Gases entering through the inlet
pipe have to reverse their direction of flow before they
can leave through the outlet pipe.

figure 15.24

figure 15.25

Engine end of an exhaust system with a catalytic converter FORD

Figure 15.26 shows a different type of catalytic
converter. This has a catalytic converter chamber
attached to the exhaust manifold. The chamber holds a
ceramic core with the catalyst. The chamber is bolted
to the manifold and can be dismantled to renew the
catalyst if this becomes necessary.

Exhaust muffler showing construction and
gas flow

Catalytic converters
Many catalytic converters are fitted into the exhaust
system in the same way as mufflers (Figure 15.25).
They are used to control exhaust emissions. Chemical
action with the exhaust gas as it passes through the
converter reduces the emissions that are discharged
from the tail pipe.
One of the features of catalytic converters is that
they operate at higher temperatures than mufflers.
They are fitted with a heat shield to prevent heat from
radiating to the bodywork and adjacent parts.
■ Care should be taken to avoid burns when working
on or near a hot exhaust system, particularly with
catalytic converters.

figure 15.26

Exhaust manifold with a catalytic converter
DAIHATSU

Exhaust-system service
The exhaust system should be free of leaks, vibration
and rattles. It should also offer a free passage for the
exhaust gases.
Leaks can occur at joints in the system, or as a
result of corrosion of the muffler or pipes. Corrosion is
caused by acids in the exhaust gases that gradually
corrode the metal. This can occur more rapidly in
vehicles that are used on short trips because the
exhaust system does not become very hot.


213-246_May_chap 15

12/9/06

10:07 AM

Page 244

244 part two engines and engine systems
To reduce corrosion, many exhaust systems, including replacement systems, are made of stainless steel.
Removing and replacing a muffler
Removing a muffler
Mufflers and exhaust pipes are not always easy to
remove because they become corroded together and
the joints are hard to separate. Some points relating to
removing a muffler are:
1. Loosen or remove the clamps on the pipes.

2. Remove the mounting brackets or rubber insulators.
3. Jack up the body, if necessary, to provide clearance.
4. Separate the joints and remove the muffler.
If the joints cannot be separated easily, then it might be
necessary to do one or more of the following:
1. Tap around the joint to free it up.
2. Use a cold chisel or special tool to expand the outer
pipe at the joint.
3. Use penetrating oil.
4. If the muffler is not being used again, cut the inlet
and outlet pipes at the muffler.
Replacing a muffler
When fitting a muffler:
1. Apply exhaust sealer to the ends of the pipes.
2. Slide the muffler into position over the pipes,
making sure that it is positioned correctly.
3. Fit the clamps loosely.
4. Attach the brackets and insulators but do not
tighten.
5. Align the parts of the system.
6. Tighten the clamps and brackets.
7. Start the engine and check for exhaust leaks.
Aligning the exhaust system
The parts of an exhaust system must be installed
correctly so that they are not under strain.
Where vibration is a problem, the mountings and
joints should be loosened completely and the parts of
the system realigned so that the supports and insulators
are all in a neutral position. The flanges, joints,
brackets and supports can then be retightened.

Figure 15.27 shows the various joints and supports
of an exhaust system which can be adjusted to provide
correct alignment of the system. Other systems might
have different mountings and fittings, but can be
aligned in a similar way.

Exhaust-system problems
Following are some exhaust system problems and
ways in which they are corrected. Refer also to
Table 15.1, which shows exhaust problems and their
likely cause.
Exhaust leaks
Leaks in the system can be located by exhaust noise, or
by grey to white deposits on the surfaces of the pipes
or muffler. Leaking joints that are otherwise in good
condition can be refitted after being coated with
muffler putty or sealer. If corrosion has occurred, the
muffler or pipe must be replaced.
Vibration
Vibration of the exhaust system can be caused by loose
mountings or connections, or by parts contacting the
body. Correct by realigning the system. Loose baffles
in a muffler will vibrate.
Back pressure
Back pressure in the system will prevent free flow of gas.
This can sometimes be indicated by a muffled exhaust
note from the tailpipe, or dampened exhaust pulsations.
Back pressure can be caused by a blocked muffler,
catalytic converter or a restricted pipe. The use of

incorrect fuels, fuel additives or combustion soot can
block the converter. Some engine pipes have a double
wall to reduce noise, and corrosion of the internal pipe
might not be obvious. Back pressure can be measured
by inserting a fitting in the exhaust pipe just after
the manifold and before the catalytic converter. Back
pressure guages are available for this purpose.
Exhaust noise
Excessive exhaust noise from the tailpipe can be due to
a muffler or resonator in which the baffles have
corroded so that they are no longer effective. Leaks at
the joints will cause exhaust blows.


213-246_May_chap 15

12/9/06

10:07 AM

Page 245

chapter fifteen intake and exhaust systems
Engine bracket

Resonator joint

Muffler joint

3

2
1
catalytic
converter

4

table 15.1

Muffler bracket
and insulator

An exhaust system with its joints and mountings

tailpipe

6

5

Manifold joint

figure 15.27

muffler

resonator

FORD

Exhaust system problems

PROBLEM

LIKELY CAUSE

Exhaust noise

Leaks at the joint between the exhaust manifold and the pipe

Exhaust gas leak

Faulty gasket between the manifold and the cylinder head
Burnt out muffler
Damaged catalytic converter
Burnt out or corroded pipe
Poor pipe joints

Rattling noises

Loose muffler baffles
Catalytic converter faulty
Pipes contacting the body
Loose or worn mountings

Engine power loss

Restricted muffler
Clogged catalytic converter

Damaged or restricted exhaust pipe

Tailpipe bracket
and insulator

245


213-246_May_chap 15

12/9/06

10:07 AM

Page 246

246 part two engines and engine systems

Technical terms
Filter, filter element, backfire, ducting, oil-wetted,
oil-bath, cellulose, porous, cyclone filter,
thermostatic, thermosensor, manifold, crossflow
head, heat transfer, plenum chamber, thermal
expansion, flanged joint, align, alignment, spherical,
extractor pipes, scavenging, muffler, resonator,
silencer, perforated, resonance, pulsating, inhibit,
catalyst, catalytic converter, back pressure, baffles,
penetrating oil.

Review questions

7.

Why are some intake manifolds heated?

8.

Name the parts of a multipoint EFI intake
system.

9.

What would be the effect of an air leak at a
connection after the air cleaner?

10.

What would be the likely effect of an air leak
after the throttle body of an EFI intake system?

11.

Name the parts of an exhaust system.

12.

What is likely to cause vibration in an exhaust
system?

13.

Why is a catalytic converter used?

14.

How does a catalytic converter differ from a
muffler?

15.

How would you go about aligning an exhaust
system?

1.

Why is air cleaned before it enters the engine?

2.

Name the main types of air cleaners.

3.

Describe the action of one type of air cleaner.

16.

What would cause the exhaust to be noisy?

4.

How are dry-type air cleaners serviced?

17.

How can exhaust leaks be detected?

5.

What is the purpose of the muffler?

18.

6.

How is heated air provided to a carburettor?

What are some of the points to be considered
when removing a muffler?