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Automotive mechanics (volume II)(Part 3, chapter20) diesel fuel system service

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Chapter 20

Diesel fuel system service

Servicing fuel filters
Bleeding and checking the fuel system
Injector service
Removing and installing injectors
Servicing injectors
Injector testing
Injector faults

Removing and installing injection pumps
Spill-timing an in-line pump
Injection pump servicing
Diesel engine problems
Checking diesel electronic controls
Technical terms
Review questions

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392 part three diesel engines
A diesel engine needs clean fuel, regular servicing of
fuel filters, tight leak-free fuel connections, and
external cleaning as part of its general maintenance.
Injectors need servicing at regular intervals, but
injection pumps should require very little service if the
other parts of the fuel system are correctly maintained.
In addition, the air cleaners, while not directly part
of the fuel system, must be serviced regularly so that
the engine is always supplied with clean air for use
with the fuel.
Servicing fuel injection components is a specialised
field. However, this chapter will provide an appreciation of how this type of servicing is carried out.

Servicing fuel filters
Because of the very small clearances in the injection
pump and the injectors, diesel fuel must be kept clean.
All necessary precautions should be taken when
handling or storing fuel so that it does not become
Also, it is important to make sure that poor
servicing does not affect the fuel after it is put into the
tank of the vehicle. Dirty fuel will not only cause

engine operating problems, but it will also damage
injection components and result in costly repairs.
The following are some general points that relate to
servicing fuel filters:
1. Before servicing a filter, clean all external oil and
dirt from around the filter. Maintain clean
conditions throughout.
2. If fitted with a drain plug, drain the filter before
removing the filter bowl.
3. After removing the canister or bowl, clean inside
the filter head with a lint-free cloth and diesel fuel.
Also clean the bowl.
4. Inspect the sealing ring and renew it if it is not in
good condition.
5. When installing, tighten the filter canister or the
filter centrebolt correctly.
6. After installing or assembling the filter, prime and
bleed the system and check for fuel leaks.

figure 20.1

Removing and installing a canister-type fuel
filter TOYOTA

Before installing, the filter seal should be coated
with fuel. When installing, the filter is hand-tightened
until the seal makes contact, then the filter is tightened
about an extra half-turn.
Some sedimenters can be drained to remove water and
deposits. The sedimenter is then flushed by using the
hand-priming pump. Some sedimenters have a bowl
that can be removed and cleaned. Others have a throwaway canister.
To check the operation of a sedimenter water-level
switch, the warning device is removed from the top of
the sedimenter (in some cases from the bottom) and
the switch operation is checked with an ohmmeter as
shown in Figure 20.2.
Filters with disposable elements

Canister fuel filters
Canister filters, or throw-away filters, are threaded onto
the filter housing. When servicing the filter, the complete
canister is removed and discarded. The filter can be
removed with an oil filter tool, but when the new filter is
installed it should be tightened by hand (Figure 20.1).

The type of filter shown in Figure 20.3 has a disposable element. The bowl is held to the top cover by a
centre bolt. A plug in the bottom of the centre bolt
allows the filter to be drained before the bowl is
removed. After removing, the bowl is washed in clean
fuel and a new filter element is installed.

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chapter twenty diesel fuel system service

figure 20.2

Removing and checking a sedimenter
warning switch TOYOTA

figure 20.3

Fuel filter with a disposable element

figure 20.4

Strainer used with a banjo connection


Strainers of fine mesh are fitted to some systems.
A strainer can be used at the fuel tank, the supply
pump, or at a banjo connection (Figure 20.4).
Strainers are serviced by washing in fuel and blowing

Bleeding and checking
the fuel system
Air will enter the fuel system if there is a leak, or if a
filter or any other part of the system has been removed.
With air in the system, the injection pump will not be
able to provide proper pressure, and injector operation
will be upset.
Fuel pumps have an overflow pipe which helps to
get rid of air from the system, and the injectors have a
leak-off pipe. Nevertheless, the system must be bled
manually as follows:
1. Loosen the bleed plug on top of the filter, which is
on the pressure side of the hand-priming pump.

2. Operate the hand-priming pump until fuel flows
from the bleed plug. Continue until the fuel is
completely free of air bubbles. Then tighten the
3. If there is a second filter, perform the same
bleeding operation.
4. Start the engine and bleed each injector pipe in
turn. With the engine idling, loosen the union nut at
the injector just enough to allow fuel to leak from
the connection. When the fuel is free of air, tighten
the injector pipe nut.
Air can be bled from the system by loosening
any of the vent plugs, or by loosening a fuel line

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394 part three diesel engines
connection. Generally, bleeding should start close to
the priming pump and follow through the system to the
injectors. Any air in the injectors themselves will be
injected into the cylinders, or will find its way to the
leak-off pipe at the top of the injectors.

■ The symptoms produced by faulty injectors in a
diesel are similar to those produced by faulty spark
plugs in a petrol engine.

■ Any air that is trapped in the system will tend to
rise to the highest point which helps it to be bled

There are a number of ways to locate a faulty injector.
Some can be carried out on the engine but others
require the injectors to be removed and tested.

Checking for fuel leaks
The fuel filters, fuel lines and various connections
should be checked for leaks with the engine running
(Figure 20.5). Parts of the system that are on the
suction side of an injection or a supply pump are below
atmospheric pressure. With faulty sealing of these
parts, air could leak into the system or fuel could leak
from the system.
On the other hand, parts that are on the pressure
side of a supply pump could leak fuel, but should not
allow entry of air.
Any leak is likely to affect the operation of the
engine. Also, distillate is an oily fuel, so any fuel that
leaks will soon collect dirt and dust and result in a very
messy engine.

figure 20.5

Locating a faulty injector

Isolating an injector
Faulty injectors can be located in some systems by
loosening off the injector pipe at each injector in turn,
with the engine running at fast idle (Figure 20.6). This
cuts off the fuel supply to the particular injector and
causes a noticeable drop in engine speed for a good
injector. However, no change in speed will occur if the
injector is faulty.
This is the same as the procedure used for bleeding
the injector pipes. If air is in the pipes and is causing
the problem, it will be bled at the same time as the
injector is being checked.
■ This procedure does not apply to electronicallycontrolled injectors.

Fuel lines, connections and components are
checked for leaks with the engine running

figure 20.6

Bleeding an injector pipe by loosening a
union at the injector PERKINS

Injector service

Checking injector spray

Injectors are designed to inject a finely atomised spray
of fuel into the combustion chamber. Faulty injectors,
which will be unable to perform that function, can
cause misfiring, engine knock, engine overheating,
loss of power, smoky black exhaust, or increased fuel
Injectors should be removed for cleaning and
testing at the recommended maintenance periods,
usually every 30 000 km.

An injector can be checked for operation on the engine
after it has been removed from the cylinder head. The
injector is fitted to its pipe, but pointing away from the
engine. The union nuts of the other injectors must be
loosened, if they are still in place, to prevent fuel from
being injected into the cylinders.
The engine is cranked over with the starter so that
the injector sprays into the air and the pattern of the
spray can be observed. It should be a uniform fine

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chapter twenty diesel fuel system service


spray, with no indications of wetness, streaks, side
sprays or dribbles (Figure 20.7). When cranking is
stopped, the nozzle should cut off and not dribble.
■ Hands must be clear of the injector while the
engine is being cranked. See the safety note in later
section ‘Injector testing’.

figure 20.7

Injector operation
(a) spray pattern when pressurised (b) condition when cranking stopped

Testing an injector
A faulty or doubtful injector should be removed from
the engine and pressure-tested on an injector tester.
The method is outlined later in the section ‘Injector
As well as bench testing, test equipment is available
for pressure testing the injection of an engine while it
is running. This consists of gauges, valves and fittings.
Basically, a pressure gauge is connected between
the injection pump and the injector and this checks the
operating pressure. This information is then used to
assess the condition of the injector and, to some extent,
the condition of the injection pump.
figure 20.8

Removing and installing injectors
When removing an injector, the injector pipe should be
disconnected at both the injector and the pump end so
that it is quite free. Removing an injector with the pipe
disconnected only at the injector could bend the pipe.
It will then be hard to reconnect.
The leak-off pipe is attached to the top of the
injector by nuts or by a union. This pipe is also
completely removed.
Most injectors for smaller diesel engines are
screwed into the cylinder head. These are removed
with a special spanner that fits on to the body of the
injector (Figure 20.8).
Flanged injectors are secured to the cylinder head

Removing threaded injectors from the
cylinder head TOYOTA

by bolts or studs. When the bolts or nuts are removed,
the injector can be loosened with a special tool or
lever, if necessary, and then removed from the recess
in the cylinder head (Figure 20.9).
Installing injectors
Before installing an injector, the recess in the cylinder
head and the end of the injector must be clean. The
washers and heat shield for the particular injector must
be in place. Some points that relate to installing an
injector are as follows:

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396 part three diesel engines
a spanner until the pipe is firmly in position. Do not
5. Leak-off pipes. These are installed in place on, or
near, the top of the injectors.

Servicing injectors

figure 20.9

Flanged injectors are held in the cylinder
head by bolts

1. Threaded injector. Check that it screws easily into
the cylinder head. After seating on the sealing
washers and heat shield, the injector is tightened to
a specified torque (Figure 20.10).
■ Overtightening could cause the nozzle to deform
and the needle could stick.

Injectors can be pressure-tested with an injector tester,
sometimes referred to as a ‘pop’ tester. The tester is
used to check the condition of injectors when they
have been removed from an engine and before they are
dismantled. The tester is also used to check and adjust
injectors after they have been dismantled and cleaned
or repaired.
Injector service includes dismantling, cleaning,
reassembling and then pressure testing. With some
types of injectors, the nozzle and needle can be
reconditioned but, with other types, the nozzle will
have to be renewed if it is in poor condition.
Diesel fuel injection workshops have special
reconditioning and testing equipment. They specialise
in the repair of injectors and injection pumps and often
provide exchange injectors.
The method of dismantling injectors is outlined
under the headings that follow. Screw-type injectors
and flanged injectors have different constructions and
so have different dismantling procedures. As well as
these there are injectors that are not designed to be
Dismantling a threaded injector
The injector to be dismantled is held in a special tool
in a vice. The nozzle holder is held by the tool and the
injector body is unscrewed from it (Figure 20.11).
These two main parts are then separated so that the
inner parts of the injector can be removed.

figure 20.10

Installing injectors: they should be tightened
to a specified torque – the sealing washer is
used at the base of the injector TOYOTA

2. Flanged injector. Check that it is a free fit in the
recess. Use a new copper sealing washer. Tighten
the bolts or nuts evenly so that the injector is not
3. Injector pipes. When being installed, the injector
pipes should be checked at both ends to see that they
fit squarely before the union nuts are connected.
4. Union nuts. Tighten the union nuts at both ends of
the injector pipes by hand. Then tighten them with

figure 20.11

Dismantling a threaded injector

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chapter twenty diesel fuel system service


A dismantled injector of this type is shown in
Figure 20.12. The shims are used to adjust the injector

figure 20.13

Dismantling a flanged injector
(a) loosening nozzle nut (b) removing nozzle
(c) nozzle removed from holder LUCAS/CAV

figure 20.12

Dismantled parts of a threaded injector – the
heat shields and washers are fitted under
the injector when it is installed

Dismantling a flanged injector
The injector is held in a bench fixture for dismantling,
as shown in Figure 20.13. The nozzle is held on the
nozzle holder by the nozzle nut. Unscrewing the nut
allows the nozzle to be removed.
There are various designs of flanged injectors and
so the procedure for dismantling and reassembling
varies. The dismantled injector shown in Figure 20.14
has a threaded adjusting nut at the top for adjusting the
The injector is dismantled from the top first. The
adjusting nut and spring are removed to relieve the
spring loading from the needle. This is done before
dismantling the bottom of the injector.
Other injectors are dismantled in a similar way, but
some have a shim adjustment instead of a screw-type
Cleaning the nozzle and needle
After dismantling, the nozzle is examined for carbon
deposits. The needle should not stick and should lift

figure 20.14

Dismantled flanged injector
1 cap nut, 2 adjusting nut, 3 nozzle holder,
4 spring and seat, 5 spindle, 6 nozzle, 7 needle, 8 nozzle nut,
9 leak-off connections, 10 assembled injector LUCAS/CAV

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398 part three diesel engines
out freely as it is removed from the nozzle. The nozzle
and needle should be clean and not damaged or blued
from overheating.
Wash the nozzle and needle in clean fuel. Use a
wooden stick to clean the needle and a brass-wire
brush to clean the outside of the nozzle (Figure 20.15).
A pintle-type nozzle is shown.

figure 20.16

Checking the needle for free movement in
the nozzle
(a) withdrawing the needle (b) releasing TOYOTA

4. Recheck the parts if the needle sticks, otherwise
renew the needle and nozzle.
■ Needles and nozzles are matched parts and so
needles cannot be interchanged between nozzles.
Cleaning a multihole nozzle
figure 20.15

Cleaning a pintle-type nozzle and needle

After cleaning, inspect the seat in the nozzle for burns
and corrosion and check the end of the needle for wear.
With the nozzle and needle wet, check that the
needle moves freely in the nozzle (Figure 20.16).
During the check, do not touch the mating surfaces of
the parts. The clearance between the parts is so small
that expansion from body heat is sufficient to alter the
fit of the needle in the nozzle.
To carry out the check, proceed as follows:

The use of a nozzle-cleaning kit is shown in Figure
20.17. This has a brass-wire brush for removing
carbon, brass scrapers for cleaning the internal
passages, and a probing tool for cleaning out the spray
holes in the end of the nozzle.
The cleaning procedure is shown in diagrams 1 to 8
in the illustration, corresponding to the following
1. Remove carbon from the tip of the nozzle with the
brass brush.
2. Clean the small feed channels with a suitable piece
of wire or a drill.

1. Hold the nozzle at about 60° and pull the needle out
about one-third of its length.

3. Clean the fuel gallery with the special groove

2. Release the needle – it should sink down smoothly
into the nozzle by its own weight.

4. Clean the end of the nozzle with the shaped scraper.

3. Repeat the test, rotating the needle slightly each
time so that it is tested in different positions.

5. Clean the seat in the nozzle. The tool is tapered like
the needle, but it has a flat side which acts as a

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chapter twenty diesel fuel system service

figure 20.18

figure 20.17

Cleaning a nozzle and needle


Using an injector tester



A different design of tester is shown in Figure
20.19. This enables the parts of a tester to be seen. It
consists of a pumping element that is operated by a
hand lever and a pressure gauge that can be isolated by
turning the hand wheel of a check valve. It also has a
fuel reservoir and a filter. Distillate or special test oil is
used in the tester.
Before making the test, the check valve is closed to
isolate and protect the pressure gauge. The hand lever
is then moved up and down quickly several times to
remove air from the injector.

6. Clean the spray holes with a short piece of fine wire
held in the probing tool. Insert the wire in the spray
hole, and turn and push it carefully until the hole is
clear and the wire enters freely.
7. Clean the needle by brushing the tip with a brasswire brush.
8. Reassemble the nozzle to the holder.
Reassembling an injector
Reassembling an injector is the reverse procedure to
dismantling. Particular attention must be paid to
cleanliness. The parts of an injector are tightened to a
specified torque. Overtightening will cause distortion.

Injector testing
There are various designs of injector testers, but they all
have the essentials of a high-pressure pump, a gauge, a
hand valve and a method of holding the injector.
An injection tester is shown in Figure 20.18. For
testing and adjustment, the injector is connected to the
tester and subjected to high pressure. This enables the
pressure setting and spray pattern to be checked.

figure 20.19

An injector tester
1 fuel container and filter, 2 check valve, 3 airbleed screw, 4 injection pump, 5 hand lever, 6 pressure
gauge, 7 pipe, 8 injection pressure-adjusting screw, 9 locknut

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■ For safety, the operator must be clear of the nozzle
when spraying. The spray has a very great penetrating force and under no circumstances should it
be allowed to come into contact with hands.
Injector tests

atomised spray of uniform pattern should be produced.
Good, fair and bad patterns are illustrated in Figure
■ The spray form will vary for the different types of
injector nozzles.

Using the injector tester, tests are made for the
following conditions: opening pressure, leakage and
spray. These are for the normal, hydraulic-operated
injectors. They do not apply to electro-hydraulic
injectors as used in common-rail injection systems.
Injector opening pressure
The opening pressure of an injector is checked by
building up pressure with the pump lever. When
nearing opening pressure, the lever is then moved
slowly downwards until the needle valve opens. At this
point, the injector sprays and the pointer of the
pressure gauge flicks. This is the opening pressure.
The pressure gauge can be graduated in bars or in
kilopascals (kPa). The opening pressure of injectors is
around 15 000 to 18 000 kPa, or 145 to 175 bars.
■ A bar is the atmospheric pressure at sea level.
Depending on the injector design, its opening
pressure is adjusted by increasing or decreasing the
thickness of the shims against the injector spring.
Where the injector has a threaded adjustment, the
pressure is set by screwing the nut up or down to
increase or decrease the force of the spring.

figure 20.20

Spray from injector nozzle showing good, fair
and bad conditions
(a) before injection commences (b) during injection (c) after
injection ceases

Injector faults

Seat tightness

A fault-finding chart is shown as Table 20.1. This sets
out some of the general faults that could be found
when testing injectors.
Where the injector does not test correctly and the
fault cannot be rectified by cleaning, the nozzle and
needle will have to be renewed or reconditioned.
Needles with uniform tip angles can be restored by
grinding the tapered end on a special machine. The
nozzle can be restored by lapping the needle seat in the
end of the nozzle. This is the type of work that is
performed in specially equipped diesel workshops.

The tip of the nozzle should remain almost dry under a
pressure of about 10 bars below the injector’s opening
pressure. At this pressure, there should be no tendency
for a drop to form on the tip of the injector.

Removing and installing
injection pumps

Back leakage
The pressure is brought up to just below injection
pressure, and the hand lever is released. The time taken
for the pressure to drop back is then noted. For
example, a drop from 150 to 100 bars in 6 seconds
could be acceptable. If the back leakage is faster than
this, it indicates excessive clearance between the
needle and the nozzle, or a possible leak between the
nozzle and the nozzle holder.

Spray form
With the check valve closed, the hand lever is operated
smartly and the spray pattern is observed. A finely

Injection pumps are mounted to the engine in a number
of different ways. There are also different ways in
which they are driven, so there is no set procedure that
applies to all injection pumps.

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table 20.1 Injector fault-finding chart



Needle does not buzz while injecting

Needle too tight, or leak past needle

Clean nozzle – if necessary, renew
nozzle and needle

Nozzle opening pressure too high
or too low

Needle seized, corroded
Needle seized, dirty
Nozzle openings clogged

Adjust for specified pressure
Renew nozzle and needle
Clean nozzle
Clean nozzle

Nozzle pressure too low

Pressure spring broken

Renew spring and readjust pressure

Nozzle drip

Nozzle leak due to carbon deposit
Sticking needle

Clean nozzle – if fault persists, renew
nozzle and needle

Form of spray distorted

Excessive carbon on needle tip
Injection holes partially blocked

Clean nozzle and needle
Clean nozzle and needle

Excessive back leakage

Needle loose fit
Foreign matter on nozzle faces and
Nozzle cap nut not tight

Renew nozzle and needle

Faulty fitting, tightening or cooling

Renew nozzle and needle
Check cooling system

Nozzle blueing

Injection pumps are driven at camshaft speed and
are timed to inject at a specified number of degrees
before TDC on the compression stroke. An injection
pump that has been removed must be reinstalled so
that the injection timing is correct. Timing marks are
provided for this purpose.

Tighten cap nut after inspecting joint

In the arrangement shown, the pump drive pulley
has to be removed before the pump can be dismantled
from the engine. This means that the timing belt also
has to be removed and so care must be taken that the
camshaft timing is not disturbed.
Timing marks

Distributor injection pump
Figure 20.21 is an example of the arrangement for a
distributor-type pump. This has a toothed pulley that is
keyed to its shaft. The pulley is driven by the timing
belt. Before the pump can be removed, the injection
inlet pipe, the outlet pipe, or fuel return line, and the
injection pipes have to be removed. The connecting
plugs will also have to be removed from electronicallycontrolled injection pumps. With these parts removed,
the pump can then be unbolted from its mounting.
Distributor-type injection pumps have a mounting
flange at the front of the pump, and this is bolted to a
mounting on the rear of the timing case of the engine.
The bolt holes are slotted to allow the pump to be
turned on its mounting for injection-timing adjustment
(Figure 20.22).
Before loosening the mounting nuts to remove the
pump, check the flange and its mounting for timing
marks. If there are no marks, then the parts should be
marked so that the injection pump can be reinstalled in
its original timing position.

Figure 20.23 shows the timing belt with the pulleys for
the crankshaft, camshaft and the injection pump. All
three pulleys have timing marks and these should be
aligned and checked before the timing belt is removed.
They should also be aligned when the timing belt is
reinstalled. This will give correct valve timing and
correct injection timing.

In-line injection pump timing
With in-line injection pumps, there are two timing
marks, one on the engine and one on the injection
pump. The timing mark on the engine could be located
on the vibration damper, on the pump coupling, or on
the flywheel.
The following are general points that relate to
installing an injection pump:
1. The engine is set on the timing mark, with No. 1
piston on the compression stroke. This is the point
where injection should commence.

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402 part three diesel engines

figure 20.21

A distributor pump and associated parts removed from an engine

figure 20.22

Timing marks on the engine and flange of a
distributor pump TOYOTA

2. The injection pump is set in the position where it is
just starting to pump fuel to the injector in No. 1
cylinder. This position is identified by a mark or
pointer on the pump and a corresponding mark on
the pump coupling.
With both the engine and the pump set to their
correct injection positions, the pump is installed on the
engine. The timing marks are checked and adjustment
made if necessary.
The general procedure for injection pump timing
has been outlined above, but the actual procedure will
vary with different engines and with different pumps.

figure 20.23


Timing belt and pulleys, including a pulley for
the injection pump – the pulleys have timing
marks TOYOTA

Two examples of timing marks for an in-line pump
are shown in Figure 20.24.
The pump in Figure 20.24(a) has an open type of
coupling which enables the timing marks to be readily

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delivery valve holder and remove its valve, spring
3. Replace the delivery valve holder and attach
a ‘gooseneck’ spill pipe to it. This is shown in
Figure 20.25.

figure 20.24

In-line injection pump timing marks
(a) marks on coupling and pump (b) marks on
coupling, timing case and pump
figure 20.25

Spill-timing an in-line injection pump – the
delivery valve, spring and volume reducer
are shown in the inset LUCAS/CAV

The pump in Figure 20.24(b) is flange-mounted to
the rear of the timing case. There is a timing mark on
the pump flange and a corresponding mark on the
timing case. The pump coupling is inside the timing
case. This also carries a timing mark that is aligned
with a pointer on the timing case. These two marks are
accessible through an aperture in the timing case after
removing a small cover.

Spill-timing an in-line pump
If an in-line injection pump has no timing marks, or if
these need to be verified, the point at which injection
commences can be found by spill-timing. This point is
where the plunger, moving upwards in its barrel, closes
off the fuel inlet port. When the inlet port closes,
injection is about to commence.
The procedure for spill timing is as follows:
1. Set the engine with No. 1 cylinder on compression
stroke, with the engine timing mark in line with the
2. Disconnect the injector pipe for No. 1 cylinder from
the delivery valve on top of the pump. Unscrew the

4. Operate the priming pump to obtain a continuous
flow of fuel from the spill pipe. If there is no flow,
rotate the pump a little.
5. With the injection pump drive coupling loose, turn
the injection pump flange slowly in the direction of
rotation. The plunger of the pump element will rise
on its pumping stroke.
6. Turn the pump very slowly and carefully observe
the flow of fuel from the spill pipe. As the plunger
rises in its barrel, the fuel from the spill pipe will
decrease to a drip. When the inlet port becomes
fully closed, the fuel will cut off completely.
This point is referred to as spill cut-off. It is
when there is no drip from the spill pipe during a
period of about 15 seconds.
7. Secure the pump drive coupling in this position,
that is, with the engine on its timing mark and the
injection pump at spill cut-off position.
8. Remove the spill pipe, replace the parts in the
delivery valve holder and reconnect the injector

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404 part three diesel engines
■ If the fuel supply to the pump has been disconnected, then the pump will have to be primed
and bled before commencing the procedure.

Injection pump servicing
Any work that has to be carried out on injection pumps
that goes beyond removal and replacement or on-thevehicle adjustments requires special facilities. These
include an air-conditioned room, an injection pump
testing machine and special tools.
Also required, for each model of pump, are specifications and data related to pump adjustments, torque
settings of bolts and screws, and performance figures
for testing purposes.
Injection pump overhaul is outside the normal
scope of a mechanic’s work. However, some idea of
the general procedures that are carried out during
pump overhaul is desirable and the following paragraphs are intended to provide only that. They do not
describe overhaul procedures.
■ Apart from specialised equipment, injection pump
work also calls for cleanliness, accuracy and
attention to detail.

figure 20.26

Pump overhaul
When an injection pump is removed from an engine, it
can be set up on a test bench to check its condition or
to locate faults. Repairs or adjustments are then made
on the basis of the test results.
An injection pump consists of a large number of
fairly small parts, which are separated during dismantling. The number of parts can be appreciated by
referring to Figure 20.26, which shows a dismantled
distributor pump. The parts would be identified as they
are being dismantled and be subjected to a visual
The pump shown is a fairly basic distributor pump,
but some pumps, such as those used with turbocharged
engines, will have additional parts.
Many parts of a pump are mated assemblies that
have been lapped together during manufacture. These
must be kept together and, if either part is excessively
worn, the assembly must be renewed.
All dismantled components are closely inspected.
Any component that shows signs of fretting, damage,
wear, corrosion, cracks or distortion is discarded and
replaced with a new part.

Dismantled parts of a basic distributor-type injection pump


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chapter twenty diesel fuel system service

During pump overhaul, all O-rings, seals, gaskets,
tab washers and locking devices that are removed are
renewed. Protection sleeves are used when installing
seals to prevent damage. All seals are coated in clean
test oil prior to assembly so that they do not operate
dry and become damaged as a result.
Injection pump testing
A fuel-pump test bench, with a distributor pump
installed, is shown in Figure 20.27. Testing machines
of this type have a variable-speed electric motor to
drive the pump and a bracket on the bed of the
machine on which the pump is mounted.
The test bench has a set of matched injectors that
are operated by the pump and graduated test tubes to
collect and measure the fuel from the injectors. There
are also various instruments including pressure gauges
and a tachometer. In addition, some test benches have
electronic measuring equipment.
■ To provide uniform results, a special test oil is used
instead of distillate.
The pump is connected to the injectors of the test
bench by a set of injector pipes. This enables the
pump, when driven by the machine, to deliver test oil
to the injectors. The pump is driven at a range of
speeds that are specified in the test data.
A graduated test tube measures the delivery of test

figure 20.27


oil from each injector during a specified period. The
quantity delivered is compared to specifications and
also with the quantity delivered by the other injectors.
Some test benches have electronic equipment that
accurately measures fuel flow and provides other
information during the test. This is displayed in graph
form in colour on the screen of the instrument.
Injection pumps can be tested for:
1. pump output
2. maximum fuel setting
3. governor action
4. feed pump operation and pressure setting
5. timing advance device operation.
The internal timing of the pump is also adjusted and
checked in relation to the timing mark on the flange of
the pump housing.
The pump output, or fuel delivery, is checked at
full-throttle setting by measuring the volume that
passes through each injector during 200 pump cycles.
■ Test oil also protects operators against the effects
of prolonged contact with distillate.
Testing and adjusting in-line pumps
In addition to the other bench tests, in-line pumps must
be phased and calibrated as part of the overhaul and
test procedure. This is done to ensure that all the

A distributor injection pump mounted on a pump-testing machine


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406 part three diesel engines
pumping elements are operating correctly in relation to
each other.
This is the procedure of checking and adjusting the
intervals (phase angle) between successive injections.
For example, the injection pump for a four-cylinder
engine has a phase angle of 90° and a six-cylinder
engine has a phase angle of 60°.
The testing machine has a degree plate. Using spill
cut-off of No. 1 cylinder pump element as a basis, the
spill cut-off of the other cylinders is checked in firing
order. These should be evenly spaced during 360° of
pump rotation.
Adjustment of the phase angle can be made by
changing the tappet spacers inside the pump or, in
some pumps, by adjusting the tappet screws. This
causes the plunger action to start earlier or later as
required to correct the phase angle.

The injection pump is mounted on the test bench
in a similar way to the distributor pump shown previously. It is then run at speeds listed in the specification
data for the particular pump. The delivery of test oil
into the calibrated test tubes is then checked for a
specified number of shots (for example, 200). All
pumping elements should deliver the same volume
during the period of the test. This can be checked by
comparing the level of oil in the graduated test tubes.
Where there is electronic measuring equipment, the
information will be displayed.

Diesel engine problems
A fault-finding chart for starting problems is shown as
Figure 20.28, and a general engine fault-finding chart
is shown as Table 20.2. Most of the complaints shown
relate to the fuel injection system – correct operation
of the system is critical to diesel engine performance.


Exhaust smoke

The pump is tested and, if necessary, calibrated
(adjusted) so that the same volume of fuel is delivered
from each pumping element. This ensures that all the
cylinders will produce equal power.
Adjustments are made by altering the positions of the
gear segments on the sleeves. Loosening the clamp and
adjusting the gear segment turns the plunger in its
barrel, and this alters the quantity of fuel that it delivers.

Black smoke from the exhaust of a diesel engine is
caused by incomplete combustion of the fuel. Blue
smoke is produced by engine lubricating oil that finds
its way into the combustion chambers.
With incomplete combustion, the fuel system is at
fault. Either too much fuel is being delivered to the
combustion chambers, or the fuel that is being
delivered is not being sprayed properly. The hydrogen

Engine will not start

Fuel system

Injection timing incorrect
Poor cylinder compression
Starting device inoperative
Glow plug inoperative
Air intake restricted

No fuel
at injection pump

Fuel at
injection pump

No fuel in tank
Fuel tank tap ‘off’
Blocked fuel line
Faulty fuel lift pump
Blocked fuel filter
Air leaks

Air in fuel system
Control rod stuck in
‘stop’ position
Leaky delivery line connection
at pump or injector
Cut-off valve stuck
Faulty injectors
Needle stuck
Holes in nozzle blocked
Incorrect injection pressure
Broken spring

figure 20.28


Battery flat/not fully charged
Cable disconnected
Faulty starter switch
Faulty isolation switch
Faulty starter motor
Cut-off solenoid inoperative

Basic fault-finding chart for diesel starting problems

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chapter twenty diesel fuel system service


table 20.2 Diesel engine complaints and possible causes



Engine overheats

Faulty injector(s)
Injection timing
Cooling system

Test, clean and adjust
Check timing
Check and flush

Engine knocks

Faulty injector(s)
Air in system
Injection timing

Test, clean and adjust
Bleed system
Check timing

Black smoke from exhaust

Injectors dribbling
Air cleaner blocked
Injection pump timing late

Clean and adjust
Clean or replace element
Check timing and reset

Engine misfires

Faulty injector(s)
Leaky injector pipe or union
Air in system
Faulty injection pump

Test, clean and adjust
Tighten or replace pipe
Bleed system
Overhaul pump

Engine starts but will not run

Air in system
Faulty supply pump
Blocked filter
Fuel low in tank

Bleed system
Check and repair
Clean or renew element
Top up tank

Engine has low power

Injection timing late or early
Injector(s) faulty
Blocked air cleaner
Faulty lift pump not delivering sufficient fuel

Check and reset
Check, clean and adjust
Clean or replace element
Check and overhaul if necessary

Engine idles badly

Governor action faulty
Injector(s) faulty
Injection pump wear (will also cause other faults)
Delivery valve(s) faulty

Adjust where possible
Check, clean and adjust
Check overhaul or replace
Check valves and spring(s)

in the fuel combines readily with the air and burns, but
the carbon does not combine as easily, and so the
carbon that is not burnt is discharged from the exhaust
as black smoke.
A smokemeter (Figure 20.29) is used to check the
exhaust gases to determine the density of the smoke
coming from the exhaust pipe. A sample of the exhaust
gas is obtained through a pipe connected to the
engine’s exhaust and the carbon that is present is
collected on a filter.
Smokemeters usually operate by comparing the
amount of light that will pass through a sample of
the exhaust gas with the amount of light that will pass
through clean air.
Cylinder compression pressure
While not directly part of the fuel injection system,
good cylinder compression is essential for correct
engine operation. With poor compression, air
temperatures would be low and ignition difficult. This
could cause hard starting and poor engine performance.

figure 20.29

Smokemeter for checking the carbon content
of the exhaust gas of a diesel engine MAZDA

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408 part three diesel engines
Compression pressures can be checked with a
compression pressure gauge. This is a special gauge for
diesels, which have much higher compression pressures
than petrol engines. The gauge is connected to an
adaptor fitted to the glow-plug hole or to the injector
hole (Figure 20.30). All the glow plugs or the injectors
are removed, and the test is carried out as follows:

or damaged. If adding oil makes no difference, a valve
could be leaking or the cylinder-head gasket could be

1. Connect the compression gauge to the adaptor.

Checking diesel
electronic controls

2. Crank the engine with the starter through three or
four compressions and take the highest gauge
3. Repeat for all cylinders and compare the pressures.
4. If a cylinder has low compression, pour a small
quantity of engine oil into the cylinder through the
glow-plug hole or injector hole, but do not connect
the gauge.
5. Spin the engine a couple of times to allow the oil to
reach the piston rings. Make sure that there is not
too much oil in the cylinder for the compression
6. Connect the compression gauge to the adaptor and
repeat step 2.
If adding oil helps the cylinder compression, then
the piston rings and/or the cylinder are probably worn

■ Only a small quantity of oil should be used during
the test as excessive oil could cause damage.

With distributor pump systems that have electronic
controls, the injectors and the mechanical parts of the
injection pumps could have similar mechanical
problems to those without electronic control. However,
with electronic-controlled systems, there are the
additional electrical and electronic components that
have to be considered if problems arise.
Fortunately, diesel electronic systems are provided
with a built-in self-diagnosis function. This is similar
to the self-diagnosis facility provided for the engine
management systems of petrol engines.
There are two ways to access problem information.
One is by the use of a hand held scanner, or multitester, that has programs for the particular vehicle. This
is plugged into a diagnosis connector provided for the
purpose. The instrument is then able to read fault codes.
The other method of diagnosing faults uses a check
engine indicator lamp on the instrument panel. By
bridging certain terminals of the diagnosis connector,
the fault codes can be read as flashes of the lamp, once
the ignition is switched on.
The method of checking is beyond the scope of this
chapter but, as an example, a particular code number
represents a timing device malfunction, while a different
code identifies a problem with a fuel cut-off solenoid.

Technical terms

figure 20.30

Checking the compression of a diesel engine

Contamination, canister, prime, bleed, banjo connection, leak-off pipe, bleed plug, vent plug,
atomised, spray pattern, nozzle, multihole nozzle,
pintle, nozzle holder, needle, dribble, deform,
injector tester, threaded injector, flanged injector,
injector opening pressure, kPa, bar, back leakage,
seat tightness, spray form, spill-timing, spill pipe,
specifications, test data, graduated, test tube,
phasing, smokemeter, calibrating, compression,
compression gauge, compression test, diagnosis,
self-diagnosis, fault codes.

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Review questions



Compare good and bad sprays from an injector.


What checks are made before removing an
injection pump?


What checks are made before removing a timing


Explain why cleanliness is so important for
diesel fuel systems.


How are sedimenters serviced?


How is the warning-light switch on a sedimenter


What is spill-timing?

Why is it necessary to bleed a diesel fuel


Explain briefly how spill-timing is carried out.




Explain how a diesel fuel system is bled.

What is the purpose of an injection pump testing

How can a faulty injector be located on an



What is meant by phasing of an in-line injection

What is the procedure for removing an injector
from an engine?



Explain calibrating in relation to an in-line

What type of equipment is needed to service



What are the likely causes of black smoke from
the exhaust?

Briefly, how is an injector dismantled?



How is a compression test carried out on a diesel


How are fault codes accessed on an injection
system with electronic control?


How is an injector cleaned?


For what conditions is an injector tested?


What are the likely effects of a faulty injector?


What safety precautions should be observed
when checking the spray from an injector?

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