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Actuators and
Troubleshooting

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Chapter 1 Fuel Pump
1.

Fuel Pump Outline

Upon starting, fuel pump is driven by battery power and controlled by ECM, thereafter. Tube types of fuel pumps
are used: Pumps of in-tank type are installed in fuel tank and pumps of in-line type are installed outside fuel tank.
In-line type pumps are generally preferred and used due to their superior anti-noise and anti-vapor-lock
characteristics. The pump consists of a DC motor, a check valve, and a relief valve, and has relatively high
current that is controlled by control relay, etc.
In accordance with installation methods, the pumps are divided into "External fuel pump" or "In-tank fuel pump".

2.

External Fuel Pump

An external fuel pump is a fuel pump installed in line outside fuel tank, that sucks fuel by means of centrifugal
force generated by the rotating rotor of a ferrite-type motor, and provides the fuel to fuel supply line. Fuel pump
consists of rotor plate that is driven by motor, pump casing eccentrically located against rotor plate, and roller that
seals pump spacer between pump casing and rotor plate, as illustrated on fig. 1
Operation of fuel pump relies on the centrifugal force generated by rotor, that will push outer wall of pump spacer

moving along the wall, in order to generate vacuum space between rollers and pump spacer at inlet side, and
then the vacuum space will be filled with fuel. Roller's rotation will increase the space and deliver the fuel to outlet
side. Then the space will be decrease at outlet side increasing pressure to discharge the fuel. Discharged fuel
from the pump will then pass around motor's armature to open check valve and there after pass through silencer
to reach fuel line. Suction/discharge will be completed by one revolution of rotor during pump operation.
Fuel pump has operation speed of 1,700 2,500rpm, and discharge rate of about 1.5 2.5 l/min and pressure of
3.0 6.0kg/ .
Fuel line has supply pressure of 2.75 3.40kg/

regulated by fuel pressure regulator and includes silencer at

outlet side to prevent pulsation of pump.

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1)

Relief Valve (Pressure Limiter)

When fuel supply line is clogged during the pump operation, relief valve will ensure safety and avoid risk of
damaging fuel supply system and fuel leak. The valve will open, if fuel pressure reaches specified value, in order
to route the high pressure to the pump’s inlet side and then through the inside of pump and motor for preventing
cumulative pressure.

2)

Check Valve (Non-Return Valve)

Upon stopping engine, check valve located in fuel pump will close using spring force, and maintain pressure
inside fuel line to ensure easier re-start of engine, and to prevent possible vapor lock by high temperature in fuel
system.

3)

Silencer

Silencer decreases the pressure change (pulsation) and noise generated by fuel flow from fuel pump, relying on
diaphragm and orifice.
Roller-cell pump

Motor armature
Non-return valve

Suction side

Pressure side

Relief valve
Rotor race plate

Pump casing

Suction side

Roller

Pressure side

Pump spacer

Rotor plate

Fig. 1 External of Fuel Pump and Basic Configuration, Operation Principle

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3.

In-tank Fuel Pump

Fig. 1-2 illustrates typical configuration of an in-tank fuel pump. Most of in-tank fuel pumps are from impeller type.
The pump is installed in fuel tank, and therefore superior to external fuel pumps in the following characteristics:
- low operation noise and to less discharge pulsation of fuel
- low torque and high rev. type motor enables compact and light design
- have great characteristics to prevent fuel leak and vapor Lock.
Fuel pump consists of DC motor part and turbine pump, which are integrated using motor driven impeller and
pump chamber that includes pump casing, pump cover, relief valve and check valve. Fig. 1-2 illustrates operation
mechanism of fuel pump. When the rotation force is delivered to impeller, pressure gap will be generated by
friction between grooves around impeller and fluid. Motor operation will continue to repeat the operation, and then
fuel fluid that will generate spiral flow will pass through motor raising pressure. Then the raised pressure will open
check valve delivering fuel to outlet. Fuel pump has speed of 1,700 2,500rpm, discharge pressure of approx.
3.0 6.0kg/ . Fuel line pressure ranges between 2.75 3.45kg/ .

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1)

Relief Valve

Fuel pump operates by DC motor at constant speed, and therefore generates constant pressure of discharged
fuel, irrespective to engine speed. The discharge pressure, however is set based on high-speed operation of
engine, and then will rise too high when engine operates at low speed and consumes less oil. The abnormally
high pressure will then open relief valve, in order to lower the pressure and maintain constant fuel pressure in fuel
line that will otherwise go up abnormally higher than specified pressure value.

2)

Check Valve

As soon as fuel pump stops check valve spring will automatically close outlet, in order to maintain fuel pressure in
fuel line, and consequently prevent otherwise possible vapor lock in fuel line by high temperature during
summer-time or after stopping engine, and ensure easier start-up of engine next time. In addition the valve
prevents reverse flow of fuel due to excessive pressure in fuel line upon engine start-up.

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Motor armature

Impeller

Pump cover

Outlet
Inlet

Check valve
Relief valve

Outlet

Pump casing

Inlet
Impeller

Casing

Fig. 1-2 Basic Configuration and Operation Principle of In-Tank Fuel Pump

Fig. 1-2-1 In-Tank Type Fuel Pump Module(Ruturnless Fuel System)

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4.

Operation Checking of Fuel Pump

1) Turn off ignition switch.
2) Directly connect battery power to fuel pump drive connectors (See fuel pump test outlets in the figure). Listen
to the pump operation noise.
As the pump is located inside fuel tank, you may be hard to hear the noise. Then open fuel tank cap and listen
to the noise through filler port.
3) Install a pressure gauge at service valve or fitting surface of pressure gauge, and watch, rising fuel pressure.
(See below for more details)
4) Use an ammeter and measure current consumption of fuel pump.
5) Hold fuel hose with hand check to feel the fuel pressure.

Fig. 1-3 Checking at Fuel Pump Drive Terminal

Fig. 1-3-1 Fuel Pump Circuit

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As for the fuel pump operation voltage, measure the
voltage at the fuel pump check terminal in the engine
cranking or engine running condition.
In this case, measured voltage should be the same as
the battery voltage. If not, check the fuse, fuel pump
relay, ECM and wiring condition of the fuel pump check
terminal.

The ECM operates fuel pump when crankshaft position

sensor transmits the signal. If the fuel pump, injector
and ignition spark do not operate while cranking, check
the crankshaft position sensor.

As for the

crankshaft position sensor check, please refer to the
engine sensors section.

As for the fuel pressure check, measure the fuel
pressure at the fuel line to check whether it meets
specification or not. Please refer to the shop manual,
because measurement location and fuel pressure
varies with difference models.

*

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5.

Symptoms of Fuel Pump Failure
- Stop the engine during idling.
- In driving, acceleration is poor and bumpy or engine goes out.
- Noise of fuel pump motor is high.
- Poor or non start-up of engine.

6.

Fuel Pressure Test

1)

Fuel Pressure Regulator

Fuel amount injected by an electronically controlled engine relies on fuel pressure and length of fuel injection time.
Therefore the fuel quantity is controlled by length of fuel injection time under constant fuel injection pressure.
Then pressure gap between fuel pressure and inside of intake manifold shall be constant in order to control fuel
injection rate by the time of fuel injection of injector. For this purpose, fuel pressure regulator is installed in fuel
delivery pipe (In case of returnles fuel system it is located with fuel pump inside of fuel tank). Fuel pressure
regulator has spring seal, which is connected to intake manifold via vacuum hose effecting pressure variation in
intake pipe in order to maintain the injection pressure constantly.

2)

Returnless Fuel System

Fuel pump maintains fuel pressure approximately constant for right injection.
Two types of fuel pump are available: Return type system returns surplus fuel except for supplying into engine,
and returnless type system supplies fuel just as much as used for engine.
Fuel pressure is decided so as to enable enough quantity of fuel injected from injector and simultaneously
facilitate vaporization. In addition it is better to maintain the pressure as high as possible to restrain generation of
vaporized gas in fuel line system. However the pressure will be limited by the reliability of the system for extended
operation at higher pressure, and reliability of power supply for maintaining high pressure for extended time of
period. Returnless type's advantage over return type is to constrain fuel temperature and vaporized gas
generation as possible. When fuel is supplied to engine and returns, the fuel will be heated by engine and
become hot, and therefore it is needed for fuel to supply only at quantity used for engine. Minimizing the fuel

vapor is intended to respond to emission control regulation. Return type pumps deliver always constant quantity
of fuel, and easy for pressure control. On the contrary Returnless type pumps would require an fuel pressure
regulation mechanism. Pressure check valve is designed inside the pump to constrain the pressure at certain
level when the pressure goes beyond the level. Besides length of injector opening time is used of
micro-adjustment of fuel supply.

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Fig. 1-4 Return Type Fuel System

Fig. 1-5 Returnless Type Fuel System

3)

Fuel Pressure Test Procedure(Return Type Fuel System)

In order to release residual fuel pressure in fuel pipe line and prevent fuel from flowing out:
(1) Disconnect fuel pump harness connector at fuel tank side.
(2) Start engine, and leave it idling until stops for itself, and then turn ignition off.
(3) Disconnect battery negative(-) terminal.
(4) Connect fuel pump harness connector.
- Disconnect high pressure fuel hose at delivery side.
- Using a fuel pressure gauge adapter, install a fuel pressure gauge on fuel filter. Tighten it to the specified

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value.(tightening torque for fuel pressure gauge and fuel filter: 2.5 3.5kgm)
- Connect battery(-) terminal.
- Connect battery terminal/to drive terminal and operate fuel pump, and then check matching face with
pressure gauge and special tools for leak.
- Remove vacuum hose from pressure regulator, and close the end of the hose, and then measure fuel
pressure with engine idling. (specified value for fuel pressure: 3.26 3.45kg/ )
- Connect vacuum hose to pressure regulator, and measure fuel pressure again. (specified valve for fuel
pressure: approx. 2.75kg/ )
- If the measurements are outside the specified values, refer to <table 1>, in order to find the possible cause
and correct it.
Stop engine and watch movement of the pressure gauge's pointer. Then the shall not move. If the pointer moves
down, check the moving range and consult with <table 2> so as to find the possible and fix it.

< Table 1 >
Condition

Possible Cause

Maintenance

• Replace fuel filter
• Valve seating in fuel pressure regulator is • Replace fuel pressure
poor and therefore fuel leaks at return port
regulator
side.

Fuel pressure, low

Clogged fuel filter

Fuel pressure, too

• Valve stuck in fuel pressure regulator
• Clogged or bent fuel return hose or pipe

high

• Repair or replace hose or
pipe
• Replace fuel pressure
regulator

Fuel pressure does
not change whether
vacuum hose is
connected or not.

• Vacuum hose or nipple is clogged or
damaged.

• Repair or replace vacuum
hose or nipple

• Valve stuck in fuel pressure regulator or
valve seating is damaged.

• Repair or Replace, Replace
fuel pressure regulator

< Table 2 >
Condition
Upon stoping engine, fuel

Possible cause

Maintenance

• Fuel leaks at injection

• Replace injector

• Check whether valve closes or
not in fuel pump.

• Replace fuel pump

pressure drops slowly.
Upon stoping engine, fuel
pressure drops rapidly.

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Chapter 2 Injector
1.

Injector Overview

Injector is a injection nozzle with solenoid that is controlled by ECM.
Using intake air quantity and engine rpm, ECM calculates basic fuel injection time, and calculates corrective fuel
injection period time on the basis of engine coolant temp, feed back signal from oxygen sensor during
close-loop-control, driving conditions including acceleration, and deceleration, and battery charging status, in
order to control injector by means of pulse signal is constant, and injecting pressure is controlled to be constant.
Then fuel injection quantity will rely on the length of time-injecting cycle in which solenoid will be magnetized and
hold needle valve open, say pulse width modulation(PWM) transmitted from ECM. The longer the injection cycle
(longer the pulse width) the more the injected fuel from injector.
As said above electronic fuel injection system operates: Injection is effected by injector. Injection quantity is
decided in accordance with injector operating time as calculated by ECM on the basis of intake air quantity, and
general driving condition.
Basically two types of system are used as follows:

- MPI(Multi-Point Injection)
- SPI(Single-Point Injection)
Both system types require electric fuel pumps that continuously deliver fuel to engine through fuel filter from fuel
tank. The fuel pump may be installed inside or outside fuel tank.
Injector injects fuel at intake manifold, and system pressure is regulated by pressure regulator so as to be
constant against intake manifold's negative pressure.
As to SPI system, gas fuel is injected by one injector located at top center of throttle valve. Distribution of air/fuel
mixture that will be delivered to each cylinder, will be achieved by intake manifold. It is not commonly used for
these days’ system because of the bad distribution.
As to MPI system, each cylinder requires one injector, that is installed intake-manifold and injects toward the
intake valve of each cylinder. Fuel supply to each injector relies on fuel rail.

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1)

MPI system

Fig. 2-1(a) illustrates typical configuration of MPI system fuel supply.
Using a number of sensors, MPI system continuously measures engine operating condition, and calculates
proper fuel quantity relying on pre-set method by ECM, so as to provide optimal fuel quantity. Therefore engine
output, engine torque, emission, fuel mileage and drivability may be provided as per engine designer's
requirement.
The calculated fuel quantity will be directly injected toward engine's intake valve, and then only air will pass intake
manifold, increasing design flexibility.
MPI System has advantages over carburetor that had been widely used until end of 1980's, as follows;
(1) Precise fuel quantity calculation under any stable conditions and temporary condition (acceleration
enrichment, warm-up enrichment, etc)
(2) No fuel stuck on inner wall of intake manifold during the fuel transfer intake manifold.
(3) Precise fuel distribution at pre-load
(4) Design flexibility for intake manifold
(5) Simple and effective use of Lambda closed loop control
(6) Low emission
(7). Easier diagnosis and repair
The above advantages may provide improved variables of engine and subsequently high output. However poor
micro-measurement in idling may be a disadvantage.

Fuel Injector
Fuel Injector

(a) MPI System

(b) SPI System

Fig. 2-1 Fuel Supply for MPI and SPI System

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Fig. 2-1-1 MPI System Overview

Fig. 2-1-2 Injector Operation Waveform

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2)

SPI System

SPI system was first introduced in 1979 by GM and Ford, and become successful by Chrysler in USA and by
Mitsubishi in Japan. Besides Bendix, Bosch, Holley and Hitachi also announced their own specific systems.
SPI system uses one injector (in case of two barrel intake manifold for V6 or V8 engines, two injectors) to inject
fuel through top of throttle plate. This type of injection requires to inject fuel through the gap between throttle plate
and intake manifold wall, and consequently cone type configuration.
Fig. 2-1(b) illustrates typical configuration of SPI system fuel supply.
SPI has many of the same advantages as MPI. To say, SPI system measures fuel quantity on the basis of
injector opening time or injection frequency, to allow easier computer-control and to provide precise fuel

measurement. In addition, the system provides advantageous installation, closed loop control, easier diagnosis &
repair, and good micro-measurement characteristics in idling with one point injection type.
SPI system however has some disadvantages as carburetor. To say, there are uneven fuel distribution among
cylinders, and fuel supply may be delayed in response to air supply. Those systems with increased active range
of injector and low fuel pressure during engine warming-up, may provide low performance. SPI system is
superior to a carburetor in performance and emission control.

Control relay

Injector
Injector side connector

Harness side connector

ECM

Fig. 2-2 Injector Circuit and Terminal
Fig. 2-2 illustrates the circuit and terminals of injector. No. 1 is the terminal that receivers injecting signal from
ECM and is controlled by power TR operation in ECM. No. 2 is the terminal receiving power from control relay.

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2.

Configuration and Operation Principle

1)

Configuration

As illustrated on fig. 2-3, injector consists of numerous parts. However the parts may be classified into three
groups: Coil assembly generates force using supplied power. Magnetic Circuit acting as path of generated
magnetism and valve group controls fuel quantity.
Coil assembly includes coil wire, Bobbin and terminals, magnetic circuit includes inlet tube, shell, armature and
seat carrier. Valve group that controls fuel quantity, includes needle assembly (Bail, Needle Shaft and Armature)
and valve seat complete (Valve Seat and Spray Hole Plate).

Valve Seat Seat Needle Shell Coil Inlet Tube Polyamid O-Ring Filter
Complete Carrier Assembly
Assembly

Fig. 2-3 Inner Structure of EV 6 Fuel Injector

2)

Operating Principle

MPI systems may be classified into two types by fuel intake line into injector. Bottom feed types take in fuel at
bottom or side and top feed types take in fuel at top. Both types use spray hole to inject measured fuel.
Fig. 2-3 illustrates the inner structure of injector. Fuel flows through filter part located at inlet to fuel measuring part.
Fuel measurement will be performed at valve seat part located to spray hole. When pulse is not adjacent
delivered to coil assembly, say power is not supplied, spring force and system pressure will press needle toward
valve seat part, in order to prevent fuel injection by injector and leakage.
When pulse is provided to coil assembly and create magnetic field, the magnetic force will pull needle from valve
seat making space for fuel passage between valve seat and needle. Fuel then will pass through the space and
thereafter spray hole to be injected outside. When coil does not receive pulse, then needle will return to close
position by spring tension.

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3.

Injector's Basic Requirements and Spray Characteristics.

1)

Basic Requirement

Injector has basic requirement that shall be ensured under all operating conditions such as short and long
injection times, cold start, hot start, etc, in the sense of flow characteristics as well as endurance characteristics.
Among the six items listed below, first five items are basic characteristics and item 6 is endurance characteristics.
(1) Precise fuel flow-rate
(2) Good linearity at low flow rate and wide active range
(3) Good spray characteristic
(4) No leakage
(5) Low noise
(6) Endurance performance

2)

Spray Characteristics

Spray characteristics may be analyzed by sprayed particulate formation, spraying pattern, and spray distribution
characteristics. Each is described below:

(1) Pencil Beam
Pencil Beam is the fuel particulate pattern injected by a single hole type injector. Basically this particulate pattern
is used at limited conditions that require particularly decided fuel particulate and spraying pattern,

Pencil Beam

Conical(Pintle)

Conical(4H)

2-Stream

Multi-Hole

Frig. 2-4 Different of Spray pattern

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(2) Conical Spray (Pintle Type Injector)
Precisely machined conical shape at end of needle valve located at fuel outlet, can respond to different spraying
angles required by engine. In addition sharp outlet edge at tip of the cone ensures better fuel particulate.
(3) Conical Spray (Four-Hole Injector)
A four-hole injector has advantages over a pintle type injector in relation with fuel particulate and spraying angle.
Each thin spray will be formed by the four holes installed on orifice plate at specific angle against injector's axial
direction. Each spray will form specific spray angle and provide better particulate effect, used together with
protective sleeve.
(4) Two-Spray Injector

Engines with two inlets per cylinder, use this injector. The center lines of sprays shall orient toward intake valves.
Then the engine requires injectors that generate two separate sprays with different spraying angles.
(5) Multi-Hole Injector
Fine holes at orifice plate enable to generate better particulate effect of sprayed fuel, and different angles of holes
prevent spray particles from confinement that may occur by reduced momentum of fuel spray.

3.

Checking of injector

Injector shall be checked for operation noise, injector's resistance, fuel injection rate, fuel spray pattern (spray
angle, rear trace, etc). However it's not easy to directly check fuel injecting rate or fuel spray pattern on a actual
car. Check connectors for connected status, and wires for disconnection and short. Check if correct injectors are
installed. Injector operation noise may be checked using a stethoscope in general, if hot engine is hard to start up,
then check fuel pressure and injector leakage. If engine cranking fails to operate injectors, check ECM power
supply circuit and grounding circuit, control relay, crank angle sensor or No1 cylinder TDC sensor for defects.
When shutting down fuel injection of injectors one by one during idling, if a cylinder is not proved to change its
idling status, check the cylinder for injector harness, ignition plugs, high voltage cable, compression pressure, etc.
In addition if injector harness and each part are checked to be normal and how ever injector operation time, say
fuel injecting time is outside the specified value, then check whether there are imperfect combustion in cylinder
(defective ignition plugs ignition coils, compression pressure, etc) and whether EGR valves operate normally.
Let’s look at the each checking methods one by one

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As for the resistance check, measure the resistance
directly after removing the injector connector. Then,

the inner coil condition of the injector can be checked.

To check the injector operating sound, contact the
stethoscope or driver to the injector while the engine is
running. The operation sound of the plunger or needle
valve can be checked.

To check the injector operation with the test lamp, connect the end of the test lamp to the positive terminal of the
battery, and connect the other end to the terminal at the ECM side of the injector. Then crank or idle the engine to
check whether the lamp blinks.
Through this test, we can check whether the ECM controls the injector or there is any wiring trouble.

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To check with the waveform, we can check the waveform at the ECM side wire. The Injector waveform should
be displayed as shown in the figure in cranking or idle state.
In injector waveforms, voltage before and after injection operation should be equal to the battery voltage. If not,
there should be a problem in the power supply system from the battery positive terminal to the injector. Besides,
voltage should be close to 0 volt as shown in the figure while the injector operates. If not, there should be problem
with the ECM and wirings from injector to ECM ground.

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4.

Fuel injection Pattern Analysis

1)

Drive Circuit of Injector

Injector drives are divided into pick and hold type injector and voltage drive type injector. In addition injectors may
be classified into low resistance injectors and high resistance injectors depending on injectors' resistance level.
Voltage drive injectors include low resistance injectors and high resistance injectors, and especially low
resistance type has coil resistance of approx. 0.6 3 , and uses an external resistance together. It is intended to
increase response and endurance of injectors, and achieved by decreasing number of winding times of
solenoids.
By reducing number of windings of solenoid coils, current is increased and injectors have better operation
characteristics. Then excessive current may flow through solenoids to damage coil or decrease endurance.
Therefore an external resistance is used together so as to avoid mentioned damages. High resistance injectors
have resistance of 12 17

to increase solenoid coil resistance for limiting current. This type of voltage drive

has simpler circuit configuration, but increase impedance, so that current at injector may be reduced to lower
sucking force of injector, and resultantly provide relatively inferior dynamic range characteristics. Fig. 2-5
illustrates example of circuit configuration of a voltage drive type injector.
Power supply

External resistance
Injector
Injection signal
Short circuit

Fig. 2-5 Voltage Drive Type Injector Circuit
Zener diode

Soho circuit
Power supply
Injector

Injection signal
Control circuit

Current detection resistance

Fig. 2-6 Peak and Hold Type Injector Circuit

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Peak and hold injectors have peak and hold circuit by ECM, and when injecting signal is on, current delivered to
injector will change. At initial stage of injector operation it flows high current to increase magnetic force and
decrease inertia of solenoid to enable initial operation, and use low current after needle valve opens. Peak and
hold type has complicated circuit configuration, but has low circuit impedance for superior dynamic range
characteristics of injector. Fig. 2-6 illustrates example peak and hold type injector drive circuit. In addition Soho
circuit in injector drive circuit protects power transistor from reverse-electromotive force generated at solenoid coil
when injection signal is off, and eliminates arc in order to reduce valve close time of injector.

2)

Measuring Fuel Injection Waveform

Use hi-scan pro oscilloscope to observe the waveform, so that you can visually check injector drive signal status
actually output from engine ECM.

Injector

Relay

ECM

External
resistance
Battery

Oscilloscope

Fig. 2-7 Fuel Injection Waveform Measurement Example Using Oscilloscope Feature

injection
period

TR : OFF

Supply
voltage
TR : ON

Fig. 2-8 Output Waveform Characteristics at Injector(+) Terminal

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Fig. 2-7 illustrates example measurement of fuel injection waveform for a voltage drive type low resistance
injection. Fig. 2-8 illustrates measurement of normal injector's waveform in idling. On fig. 2-8, the signal shows
battery voltage when ECM transistor is at off state, but waveform on the figure will be observed by effect of
external resistance when transistor is on. When transistor shifts to 'on', injector voltage would drop vertically if
injector is affected only by resistance. However reverse-electromotive force from injector coil make the voltage
drop along a curve as B. In addition when transistor moves to 'off ' injector will return to battery voltage and shut
off. Then current will rapidly shut off at coil, and consequently voltage will temporarily rise beyond battery voltage
and again become stable at battery voltage. Rising at part A represents voltage change by plunger's changed
moving speed through the magnetic field to which is generated by solenoid coil. To say it indicates, plunger
contacted at stopper or stopped. If the rising does not appear, it therefore indicates that plunger is not moving
actually-stuck and remain open or close.

Fig. 2-9 Voltage (-) Terminal Output Waveform of Drive Type Injector
Fig. 2-9, Oscilloscope B illustrates output wave form at injector grounding side (-) terminal. Injector's fuel injection
waveform is typically measured at (-) terminal. Then resulting waveform will differ by injector drive circuit. Fig. 2-9
represents output waveform at voltage drive type injector (-) terminal. Fig. 2-9 part A shows voltage supply to
injector. Part B illustrates that ECM's injector drive transistor shifts to 'on', and then injector plunger will be pulled
to stopper and fuel injection will begin. Part C represents injector's fuel injection time. Part D illustrates that current
from injector is suddenly interrupted and reverse-electromotive force is generated. Part E shows that ECM's
injector drive transistor shifts to 'off ' and fuel injection stops.

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Fig. 2-10 Output Waveform of PWM Drive Type Injector
Fig. 2-10 shows PWM(Pulse Width Modulated) injector's output waveform. A PWM injector will have high current
when injector opens initially, and during injecting period of time after opened, current applied to injector will be
on/off-pulse-controlled by means of grounding. Fig. 2-10 part A represents supply voltage from injector, part B
indicates that ECM's injector drive transistor shifts to 'on', and pulling injector plunger toward stopper, injector
starts fuel injection. Part C indicates injector's fuel injection time. Part D means the period where current flowing
through injector's solenoid coil is limited. To say initially at the time of opening, high current will flow to provide
better operation characteristics, and after opened the current will be limited within minimized level to maintain
'open' state. Part E shows magnitude of reverse-electromotive force generated at solenoid coil when injector
current is suddenly interrupted. Part F indicates that it returns to supply voltage.

Fig. 2-11 Peak and Hold Injector's Output Waveform.
Fig. 2-11 illustrates peak and hold injector's output waveform. One of typical injectors of this type is TBI(Throttle
Body Injection) fuel injection system. In fig. 2-11, part A shows supply voltage delivered to injector, part B

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indicates that ECM's injector drive transistor is on and fuel injection starts. Part C represents that high current
flows initially at opening of injector, and then the current decreases and injector solenoid coil generate
reverse-electromotive force. Part D means that after injector valve opens, minimum, level of current flows in
order
to maintain open status. Part E implies fuel injection time. Part F represents that ECM's injector drive
transistor is off and fuel injection stops, returning to supply voltage.
B. Analysis of Fuel Injection Waveform

Fig. 2-12 Analysis of Fuel Injection Waveform
Injection waveform checking at injection will be required in case of engine malfunction, lower engine output,

engine start-up being impossible or poor, sporadic vibration, etc. Injector's fuel injection waveform normally
indicates supply current as described above.
However as soon as ECM's injector drive transistor is on and transmit injection signal, the waveform will be
'on'(grounded) and almost continuously remain 'on'. In addition when ECM turns off the transistor, solenoid coil's
reverse-electromotive force will generate voltage peak and it returns to supply voltage. Therefore injector's fuel
injection waveform checking shall be focused on fig. 2-12, part A & B. part A indicates magnitude of
reverse-electromotive force. You shall check if maximum values of the force obtained from injectors of all
cylinders are constant. Typically maximum values of electromotive force are approx. above 80V. If those
maximum values differ more than 5V, then ensure that correct injectors are installed for the engine, and check
injector's power supply side and grounding side. Part B represents magnitude of voltage drop by the wiring it self
between injector(-) terminal and ECM grounding during injector driving time, say fuel injection time. Then value of
dV shall be approx. 1V or less. If the value is higher, there are some resistance element to generate voltage drop
between injector(-) terminal and ECM grounding. You shall check it. If the lower slope is rough or looks like
staircases, you shall also check injector's grounding side.

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