Isuzu L Series User manual

Table of Contents
UL-Series Diesel
Foreword 1
I. Introduction
Application Notes 2
Maintenance Schedule 3
General Family Information 4
II. Engine Component Description
Injection Pumps, Timing 5-8
Valve Train 9
Camshaft 10
Crank, Block, Pistons, Rods 11-14
Head Gasket 15
Cylinder Head 16
Lubrication 17-18
Cooling 19
III. Engine Servicing Procedures
Spill Port Timing 20
Valve Adjustment 21
Injector Service 22-24
Injector Pop-Off Test 25
Injector Leak Test 26
Glow plug Inspection 26
Hot plug Replacement 27
IV. Engine Repair Specifications – 3L 28-31
V. Engine Repair Specifications – 4L 32-35
VI. Component Failure Analysis 36-40
VII. Appendix – Misc. Service Information
Nozzle Troubleshooting Guide 41
Nozzle Performance & Diagnosis 42
Nozzle Holder Tightening Specifications 43-44
Turbo Diagnosis 45
Exhaust Temperature 46
Crankcase Pressure 46
Inlet Manifold Pressure 46
Used Oil Analysis 47
VIII. Isuzu Technology – L-Series Direct Injection 48-49

Foreword
UL-Series Diesel 1
This book is designed to cover several aspects of the L-series engines. L-series engines
currently in production are the 3LA, 3LB, 3LD, 4LB, 4LC, and the 4LE. This training
manual is divided into six sections to make referencing information easier.
The introduction covers engine application notes and maintenance schedule. Section two
is the engine component section that provides in-depth descriptions of each component.
This will include component operation and important points that are critical to the
disassembly, inspection and reassembly of the engine. Section three is the engine service
section, which illustrates important information regarding fuel injection operation and
routine fuel injection service items. Section four provides a comprehensive listing of all
the critical engine specifications for the 3L engines. Section five contains the same
specifications as they relate to the 4L engines. A broad range of component failures are
illustrated in section six. Non-L-Series specific service information on various topics is
placed in the appendix.
Due to the similarities between the 3L & 4L engines, we have created a single technician
guide to cover both engines. This training manual outlines the important aspects of the
repair manual; however, it is not a stand-alone manual. It must be used in conjunction
with the appropriate Workshop Manuals.

I. Introduction – Application Notes
UL-Series Diesel 2
The L series engines are used in a variety of
industrial applications ranging from small
generators (pictured here) and light duty farm
machinery to construction equipment. Their
compact design makes them an ideal power
system when conservation of space is of the
utmost consideration. Internally, both the 3L
and 4L engines share many similar parts. The
main difference between these engines is their
displacement and horsepower output.
Additionally, the 4L series has the option of
being turbocharged.
There are several L-series engines that are CARB (California Air Resource Board) certified.
CARB emissions standards for the L series apply to engine models in the 11-25 hp range and
25-50 hp range. To meet the new CARB standards, the pump’s injection timing has been
changed. This eliminates the cost of expensive emission control scrubbing devices. The
leaner fuel mixture (shorter injection duration) helps increase the exhaust temperatures while
lowering emissions at a fraction of the cost of scrubbing devices. Another feature unique to
Isuzu engines, is the conical shaped heat shield. This gives the incoming fuel injections a
“swirl affect” that increases atomizing for maximum combustion efficiency; this too helps
reduce exhaust emissions.
These are just some of the engineering refinements that Isuzu has implemented to stay
abreast with the latest in diesel and diesel emission technologies. In the ensuing pages, a
more thorough look at the internal components as well as fuel system will be covered.

I. Introduction – Maintenance Schedule
UL-Series Diesel 3
The following maintenance schedule is a comprehensive service program that takes a preventative
approach to engine repair. Isuzu has established these standards with maintenance as the basis for
prolonged product life. Isuzu highly recommends that if a routine maintenance schedule is not
part of your customer support service, one should be implemented to better serve the needs of
your customers.
Maintenance Item Daily 250 hrs 500 hrs 750 hrs 1000 hrs
Oil level 4
Oil leaks 4
Proper oil pressure 4
Low oil warning lamp 4
Oil filter replacement ¬4 4 4 4
Engine oil ¬4 4 4 4
Fuel leaks 4
Contaminated fuel 4
Fuel filter replacement 4 4
Injector nozzle check 4 4
Coolant level 4
Coolant leaks 4
Fan belt tension 4
Coolant temperature 4
Coolant replace Replace every 6 months
Electrolyte levels 4
Radiator fin cleaning 4
Radiator cap fitting check 4
Radiator cleaning 4
Radiator cap function test There is no service interval specification provided by Isuzu
Air cleaner check/replace Refer to element manufacturer for interval
Wire/Connector integrity There is no service interval specification provided by Isuzu
Battery charge % Refer to battery manufacturer or battery test tool for interval
Electrolyte gravity % Refer to battery manufacturer for interval
Starter cleaning 4
Generator cleaning 4
Battery cleaning 4
Pre-heat condition 4
Abnormal engine noises 4
Exhaust color 4
Cylinder compression 4
Valve lash check & set 4
¬Remove and replace after initial 50 hrs of engine operation. Then follow the regular
maintenance schedule thereafter.

I. Introduction – General Engine Family Information
UL-Series Diesel 4
L-Series Engines
Below is a brief description of the application/development criteria and design characteristics of the
L engine family:
Clean
•Individual Zexelinjection pumps w/short high pressure fuel injection pipes to reduce
volumetric loss and minimize injection delay common at high speeds.
•Ricardo Commet-V type combustion chamber
•Steel laminated head gasket and liquid gasket for other sealing surfaces means no more asbestos
•Blow-by gases recirculated into intake with use of PCV valve
Quiet
•Single OHV cam that drives injectors, intake and exhaust valves (less gear driven components)
•Large mesh area on gear driven components
•Auto-thermatic pistons that reduce engine noise at start up and after warm up.
Small size
•Overhead valve to reduce engine height
•Full siamese engine block design reduces length
Ease of Maintenance
•All service points of engine are placed on the same side
(oil fill, dipstick, filter, injection pumps, nozzles and glow plugs).
•Electric fuel pump purges air automatically
Identification
The production date for any Isuzu engine can be obtained be reading the letter codes on the ID tag
(usually located on the head cover) and using the table below.
ABC D EFG H IJ
0123456789
Example: BA/JB=10/91 (Engine produced October, 1991).

II. Engine Component Description
UL-Series Diesel 5
Pump Description
All L-series engines use individual injection pumps
to supply fuel to the injection nozzles. The fuel
pumps are mounted to the engine block, and are
operated by the camshaft. Inside of the pump, there
is a plunger barrel, timing sleeve, and plunger
assembly. The plunger barrel contains the pump’s
timing sleeve. The barrel uses a guide pin to locate
the timing sleeve in the correct position. The
internal area of the plunger barrel also serves as the
fuel reservoir. The timing sleeve fits over the
plunger and both components fit inside of the
plunger barrel
The timing sleeve component contains both the
fill port and the spill port. Fuel enters the
pressure chamber through the fill port. As the
plunger rises, it closes the fill and spill ports,
forcing pressurized fuel out the delivery valve to
the injector nozzle. Any residual fuel is bled off
through the spill port on the plunger return
stroke.
Pump timing is determined by the thickness of
shims placed between the pump housing and the
cylinder block. Each shim varies in thickness by
.1mm (.004”), creating a 1
°
change in timing
(thicker=retard, thinner=advance). The shims are
a “crush” design and must not be reused.
IMPORTANT: All pump shims must be of
the same thickness when replaced. No single
pump can have a different thickness shim
installed.
If this cannot be achieved, there could
be a problem with the injection pump. During
the warranty period, a pump requiring service
must
be returned to an authorized Zexel
distributor.
Timing SleevePlunger
Plunger
Barrel
Plunger Guide
Pin

II. Engine Component Description
UL-Series Diesel 6
Pump Timing
This drawing shows the relationship between cam lift and cam angle when pre-stroke length is
changed. The stroke length represented as “L” is always constant. When the pumps are advanced
by using a thinner shim, the timing sleeve is lowered and the start of injection occurs at the
beginning of the cam lift. (Note: the sleeve is fixed to the pump housing.)
Conversely, when the pump is retarded by using a thicker shim, the pre-stroke is lengthened
because the timing sleeve is raised. Raising the pump housing changes the start of injection to the
last half of the cam lift. It also reduces the total number of cam degrees to complete one injection.
Rack Operation
The plunger’s roller follower rides directly
on the cam lobe. Plunger position is
controlled by cam lobe lift. Rack movement
rotates the sleeve, changing the spill port
position relative to the plunger’s helix. This,
in turn, varies the amount of fuel injected.
NOTE: In order to remove the pumps from
the block, the rack slide must be centered
otherwise the pumps will hang-up on the
cylinder block casting.

II. Engine Component Description
UL-Series Diesel 7
Pump Injection Sequence
Intake
Fuel enters the high-pressure chamber
from the intake port. However, even
though the plunger begins to rise,
pressure inside the chamber does not
increase because the fuel from the inlet
port flows back into the fuel reservoir
via the spill-port hole
Beginning of Injection
As the plunger rises, it blocks the spill
port hole in the timing sleeve. The
plunger blocks the inlet port preventing
additional fuel from entering the high-
pressure chamber. It is during this
transition that pressure inside the
chamber begins to develop.

II. Engine Component Description
UL-Series Diesel 8
Pump Injection Sequence (continued)
Pressure Feeding
Since the intake port and helix are kept
closed by the timing sleeve, fuel
pressure continues to rise, the delivery
valve opens, and fuel flows to the
injector.
End of Injection
On the return stroke, when the plunger
helix reaches the timing sleeve’s spill
port, the pressurized fuel flows through
the spill port and into the oil reservoir.
At this moment pressure in the chamber
drops which ends the injection cycle.

II. Engine Component Description
UL-Series Diesel 9
Valve Train
IMPORTANT! Upon
reassembly, make certain
that all rocker springs are installed in their
correct location. Also ensure that the oil galley is
not blocked when applying liquid gasket.
L-series engines use individual rocker arms
mounted on a common shaft. The rockers and
shaft are mounted inside the rocker bracket
assembly. Both components can be removed
for servicing by simply removing the balance
shaft’s retaining plug at the rear of the bracket.
Before disassembly, note the positioning of the
left and right offset rocker arms. Off-setting
the rocker arms straightens out the push rod
angle. It also helps move the push rod end of
the rocker arm away from the bracket area to
eliminate rocker to bracket contact.
During disassembly, difficulties removing the
shafts may be experienced. This is due to the
slight interference fit in the bracket holes,
which may be compounded with varnish or
sludge build-up on the shaft.
NOTE: During reassembly, special care
must be taken to properly seal the rocker
bracket assembly. Since this is the intake
manifold, improper sealing will result in
excessive oil consumption.
The rocker shaft is oil pressure fed through a
galley machined in the cylinder head. This
galley intersects with the main oil galley in the
block to provide full pressure oiling to the
rocker arms.
Important: When replacing the head
gasket, be sure that the oil hole in the gasket
is aligned correctly with the oil galley in the
block. Failure to do so will prevent oil from
reaching the rocker shafts.
The head gasket is available in one thickness
only.
Do not seal oil galley
with liquid gasket.

II. Engine Component Description
UL-Series Diesel 10
Camshaft Design
The camshaft is a cast iron billet and has lobes
for
both
the valves
and
fuel pumps. The cam is
supported by two ball bearings and a needle
bearing (located in the center of the block) to
reduce friction and improve shaft durability.
The lifters are conventional flat tappet design,
requiring periodic valve adjustment. The
camshaft also has an oil galley drilled into the
front of the shaft that provides lubrication for
the flywheel sleeve assembly.
NOTE: It is not uncommon to see marks
that resemble tracks on the fuel pump lobe.
These are track marks from the fuel
pump’s roller lifter. This is a normal
characteristic of this design.
Camshaft Gear Timing
Correct camshaft timing is shown at the left.
The crankshaft is positioned with the key way
at the top. The crankshaft gear timing mark
will be at approximately 9 o’clock. The idler
gear is positioned with one mark at 3 o’clock
(lined up with the crankshaft’s mark), and with
a second mark at 12 o’clock. The camshaft
gear timing mark aligns with that second mark
on the idler gear.
IMPORTANT: The initial timing of these
gears is absolutely essential. Due to the
combination of different gear ratios, the
timing marks will not line-up with their
respective gears after the engine has been
rotated a few times.

II. Engine Component Description
UL-Series Diesel 11
Crankshaft
The crankshaft is forged steel with induction
hardened main and connecting rod journal
surfaces. Induction hardening is applied to the
friction surfaces of the journals, crank pins and
oil seal surfaces to improve wear resistance.
The crankshaft has the engine configuration
number cast on the crankshaft for
identification.
Each rod journal has its own set of counter
weights to simplify balancing and help reduce
crankshaft vibrations. Certain L-Series engines
are externally balanced with the use of weights
on the crankshaft damper.
NOTE: The
dampers should NEVER be interchanged.
Excessive engine vibration and damage will
occur.
IMPORTANT: The crank is hardened
using Tufftriding. Isuzu does not
recommend grinding the crankshaft
undersize.
Engine Config #

II. Engine Component Description
UL-Series Diesel 12
Cylinder Block
The engine’s serial number is stamped on the
front of the engine block. This number is used
by parts technical personnel to track an
engine's application or verify a specification.
Also shown are the castings in the block for
the individual injection pumps.
The 3L cylinder block features four main
bearing supports. The 4L block contains 5
main bearings. The caps are identified as
detailed below:
4L 3L
#1 “F” #1 “F”
#2 * #2 *
#3 “C” #3 “C”
#4 “R” #4 “C” and a “s”
#5 “R”
* has oil pump pick-up tube hole
The engine block uses cast-in-place rather than
removable liners. The block is a semi-dry deck
configuration incorporating overhead oiling
for the rockers. The cylinders and the deck
surface are cast together giving the block extra
support around the tops of the cylinders.
Coolant circulates around the periphery of the
cylinder bore area. This helps reduce piston
ring temperatures by eliminating cylinder hot
spots that are inherent with
siamese cylinder
bores.

II. Engine Component Description
UL-Series Diesel 13
Piston Sizing
Pistons are matched during assembly to the
final bore diameter and deck height
dimensions. Piston clearances are set-up at the
factory within a window to keep noise to a
minimum level; but these clearances are tight
enough to prevent piston skirt galling.
L-Series engines do not use replaceable
cylinder liners. Service grade pistons are
available for warranty repairs, in standard size
only.
If the engine is out of warranty, pistons are
available for cylinders bored .010 over. Boring
the cylinders and use of oversize pistons is not
approved for Isuzu warranty repairs.
TIP: Previously, pistons were bore sized and
identified with grade lettering for service
replacement. This system has been terminated
for the L-series engine and your parts book
should reflect the change. Please refer to
bulletin #AIPDN-PTS-ED02-98 for ordering
replacement pistons.
Note: The bore size identification stamp is
located on the block just above the fuel pump
hole.

II. Engine Component Description
UL-Series Diesel 14
Connecting Rod
A forged steel I-beam connecting rod is used
for all L-series engines. They are full floating
design with bushed wrist pin ends.
NOTE: When removing and replacing the
connecting rod assemblies, be sure to install
the connecting rod with the Isuzu Logo
facing the same direction as the piston’s
forward notch.
IMPORTANT: The rod cap bolts are not to
be removed. It is shown only for clarity, but
is not a standard rod cap bolt. These bolts
have
serrations (to prevent the bolts from
turning) and are pressed onto the rod.
When servicing, the entire rod must be
replaced.

II. Engine Component Description
UL-Series Diesel 15
Cylinder Head Gasket
IMPORTANT: The head gasket must be
installed with the flat side of the sealing
bead facing up. Also the large flat end of the
gasket must face forward.
The L-series engines use a three layer ultra
thin laminated steel head gasket that requires
no retorqueing after the engine break-in
period. Holes for coolant are drilled between
the valve seats for effective cooling of the
combustion area.
The sealing bead surrounding the cylinders of
the gasket is stainless steel. It protects the head
gasket from the high cylinder pressures. The
sealing bead also protects the gasket from the
high temperatures released by the hot plugs.
The gasket comes pre-coated with a silicon
material. Therefore, no additional application
of sealers or gasket adhesives is necessary, and
no re-
torqueing of the head bolts is required if
the prescribed angular tightening method is
used.
To identify the gallies, use the drawing and
legend below.
Legend
oCoolant
-Oil
+Bolt
xPush Rod
Head bolt
loosening
sequence.
Head bolt torque
sequence.
(See engine repair
specifications
section.)

II. Engine Component Description
UL-Series Diesel 16
Cylinder Head
The L-series cylinder heads are cast iron with
replaceable valve guides and valve seats. The
head casting number is embossed at the front of
the head’s casting just below the injector
nozzle bore.
Compression tests are conducted using a
compression gauge adapter used as a glow plug
insert, special tool number 5-88402-656-0.
Refer to workshop manual for procedure.
The service limit for this engine is 370
psi
(26.0 kg/cm
2
). Standard pressure is 441
psi
(31.0 kg/cm
2
). Isuzu allows an 8% variance
between cylinders on compression tests, but
there can be no more than a 15% difference
between any two cylinders.
Letters A-F represent the different
measurements that need to be taken to
determine head warpage.
Upper & Lower face warpage specifications:
Standard: 0.075 mm. (0.0029 in.)
Limit: 0.15 mm. (0.0059 in.)
Max Grinding Allowance: 0.3 mm. (0.0118 in.)
Head Height:
Standard: 64 mm. (2.5197 in.)
Limit: 63.7 mm. (2.5079 in.)
IMPORTANT: Valve depression must be
checked to ensure that it is still within
specification.
Casting #

II. Engine Component Description
UL-Series Diesel 17
Lubrication
Lubrication is achieved with a conventional
wet sump oiling system. Internally, the
trochoid oil pump uses a set of rotors instead
of spur gears.
It is a very efficient and smooth operating
pump. Compared with the spur gear type
pump, the trochoid pump gives practically
continuous flow, due to less leakage on the
discharge side of the pump.
The pump is mounted to the front of the
engine block and driven by the crankshaft.
On the pump’s exterior housing, there are two
lugs machined for dowel pins. This enables the
pump to be repositioned in exactly the same
location without having to set pump gear
backlash.
The pump is a serviceable unit. Internal
components are interchangeable between PTO
and non-PTO versions.
TIP: Always
remove the pump’s pressure
relief valve during a rebuild. Look for a
cocked pressure spring, burred relief valve or
burred pump housing that would cause the
pressure valve to fail. (If housing is burred, it
must be replaced.)

II. Engine Component Description
UL-Series Diesel 18
Lubrication (continued)
Below is the oil full flow diagram. Note the valve opening pressure for the oil filter bypass valve
(14 PSI is where the valve begins to open. The same is true for the oil pump relief valve, which
begins to open at 64 PSI.).

II. Engine Component Description
UL-Series Diesel 19
Cooling System
Below is the coolant flow diagram. Good coolant circulation is ensured by utilizing water
jackets formed with a one-piece casting core, which eliminates burrs in the water passage.
Maintain a coolant/water solution concentration ratio of
50
/
50
. Use only de-mineralized (soft)
water, since hard water tends to neutralize the corrosion inhibitors in the antifreeze and add
scale (particularly in hot spots) to the cooling system. It is absolutely
required
that you use a
low-silicate formula anti-freeze. Do not add any additional water pump lubricants to the
cooling system. Refer to the Workshop Manual for radiator cap and cooling system testing
and specifications.
Use a commercially available antifreeze tester when testing for coolant/water mixture. Testing
for pH is essential, as too high an acidity or alkalinity can cause severe damage to the engine
and cooling systems. The pH readings should be 7.5-8.5 (SAE J1034 allows for 7.5-11.0).
Litmus test paper is available from most commercial tool suppliers and product distributors.