Diesel fuel system service 389 Servicing fuel filters 390 Bleeding and checking the fuel system 391 Injector service 392 Removing and installing injectors 393 Servicing injectors 394 Injector testing 397 Injector faults 398 Removing and installing injection pumps 398 Spilltiming an inline pump 401 Injection pump servicing 402 Diesel engine problems 404 Checking diesel electronic controls 406 Technical terms 406 Review questions 407
Trang 1Diesel fuel system service
Chapter 20
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
Trang 2A 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
appreci-ation 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
contaminated.
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.
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).
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.
Sedimenters
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 throw-away 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
The type of filter shown in Figure 20.3 has a dispos-able 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.
figure 20.1 Removing and installing a canister-type fuel
filter TOYOTA
Trang 3Strainers 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
clean.
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 plug.
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
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
Trang 4connection 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.
■ Any air that is trapped in the system will tend to
rise to the highest point which helps it to be bled
off.
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.
■ The symptoms produced by faulty injectors in a diesel are similar to those produced by faulty spark plugs in a petrol engine.
Locating a faulty injector
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.
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 electronically-controlled injectors.
figure 20.5 Fuel lines, connections and components are
checked for leaks with the engine running
MAZDA
Injector service
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
consumption.
Injectors should be removed for cleaning and
testing at the recommended maintenance periods,
usually every 30 000 km.
figure 20.6 Bleeding an injector pipe by loosening a
union at the injector PERKINS
Checking injector spray
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
Trang 5spray, 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’.
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
testing’.
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.
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
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:
figure 20.7 Injector operation
(a) spray pattern when pressurised (b)
con-dition when cranking stopped
figure 20.8 Removing threaded injectors from the
cylinder head TOYOTA
Trang 61 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.
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
tilted.
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
a spanner until the pipe is firmly in position Do not overtighten.
5 Leak-off pipes These are installed in place on, or near, the top of the injectors.
Servicing injectors
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 serviced.
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 20.9 Flanged injectors are held in the cylinder
head by bolts
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
figure 20.11 Dismantling a threaded injector
Trang 7A dismantled injector of this type is shown in
Figure 20.12 The shims are used to adjust the injector
pressure.
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
pressure.
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
adjustment.
Cleaning the nozzle and needle
After dismantling, the nozzle is examined for carbon
deposits The needle should not stick and should lift
figure 20.12 Dismantled parts of a threaded injector – the
heat shields and washers are fitted under the injector when it is installed
figure 20.13 Dismantling a flanged injector
(a) loosening nozzle nut (b) removing nozzle (c) nozzle removed from holder LUCAS/CAV
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
Trang 8out 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.
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:
1 Hold the nozzle at about 60° and pull the needle out
about one-third of its length.
2 Release the needle – it should sink down smoothly
into the nozzle by its own weight.
3 Repeat the test, rotating the needle slightly each
time so that it is tested in different positions.
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
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 steps:
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.
3 Clean the fuel gallery with the special groove scraper.
4 Clean the end of the nozzle with the shaped scraper.
5 Clean the seat in the nozzle The tool is tapered like the needle, but it has a flat side which acts as a scraper.
figure 20.15 Cleaning a pintle-type nozzle and needle
TOYOTA
figure 20.16 Checking the needle for free movement in
the nozzle (a) withdrawing the needle (b) releasing TOYOTA
Trang 96 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
brass-wire 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.
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.
figure 20.17 Cleaning a nozzle and needle LUCAS/CAV
figure 20.18 Using an injector tester LUCAS/CAV
figure 20.19 An injector tester
1 fuel container and filter, 2 check valve, 3
air-bleed screw, 4 injection pump, 5 hand lever, 6 pressure gauge, 7 pipe, 8 injection pressure-adjusting screw, 9 locknut
LUCAS/CAV
Trang 10■ For safety, the operator must be clear of the nozzle
when spraying The spray has a very great
pene-trating force and under no circumstances should it
be allowed to come into contact with hands.
Injector tests
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.
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.
Seat tightness
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.
Spray form
With the check valve closed, the hand lever is operated
smartly and the spray pattern is observed A finely
atomised spray of uniform pattern should be produced Good, fair and bad patterns are illustrated in Figure 20.20.
■ The spray form will vary for the different types of injector nozzles.
Injector faults
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.
Removing and installing injection pumps
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.
figure 20.20 Spray from injector nozzle showing good, fair
and bad conditions (a) before injection commences (b) during injection (c) after
injection ceases