toyota training course t874 engine control systems II ch07

Section 7

Fuel Systems

Slide 79
T852f234

Fuel Systems The purpose of the fuel injection system is to precisely inject a metered
amount of fuel at the correct time. Based on input sensor signals and
internal programming, the ECM decides when to turn each injector ON
and OFF.
Port fuel injection introduces fuel into the intake manifold, where it mixes
with intake air. The air/fuel mixture then is drawn into the combustion
chamber through the intake valve. Because the timing of air/fuel entry into
the combustion chamber is controlled by the engine’s valve system, the
timing of fuel injection is less important than the volume of fuel injected.
Typical Port Injection Most port fuel injection systems have the following components:
Components
•Fuel tank and lines store fuel and route it where needed.
•Fuel filter removes impurities from fuel.

•Feed fuel pump draws fuel from the tank (under control of Fuel
Pump ECU in certain port injection systems).
•Pressure regulator controls pressure within the system.

•Pulsation damper reduces pressure fluctuations within the system.

•Port fuel injectors open and close on command from the ECM;
when an injector opens, system pressure causes fuel to flow through
the injector.

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Fuel Delivery — Return Type

Fuel Systems

Slide 80
T852f181

Return Type Fuel Delivery

In a return type fuel delivery system, fuel that is not needed for engine
operation is returned to the tank through a fuel return line. Some port
injection systems use return type delivery.
In a return type port injection system:

•When the fuel pump runs, pressurized fuel flows out of the tank,
through the fuel filter to the fuel rail and the pressure regulator.

•The pressure regulator maintains fuel pressure in the rail at a
specified value. This value will vary in relation to either manifold
vacuum or atmospheric pressure, depending on model.

•Excess fuel not needed for engine operation is returned to the tank
through a fuel return line.

Return type systems have two major disadvantages:

•The return fuel delivery system adds weight and creates more
opportunity for leakage.

•Fuel returning to the tank has been heated by the engine, which
could result in increased evaporative emissions.

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Fuel Delivery — Returnless Type

Fuel Systems

Slide 81
208EG117

Returnless Type Fuel
Delivery

In a returnless type fuel delivery system, there is no return of fuel to the
tank. This eliminates the weight and complication of return lines and the
return of heated fuel to the tank.
Many current port injection systems use returnless type fuel delivery. The
location and operation of the pressure regulator is the main functional
difference between return and returnless designs.
In a returnless system:

•When the fuel pump runs, pressurized fuel flows from the pump
to the in-tank pressure regulator. This spring-loaded regulator
maintains a set pressure value in the system (does not vary
regardless of manifold vacuum or atmospheric pressure).

•At the pressure regulator, excess fuel is directed to the bottom of the
fuel tank while pressurized fuel is sent out of the fuel tank, through
the fuel filter, pulsation damper, and into the fuel rail.
•Fuel pressure in this system is maintained at a constant and higher
pressure than in the return type fuel system. ECM programming
and a higher system pressure eliminate the need for a modulated
pressure regulator.

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Fuel Pump: In-tank Electric

Fuel Systems

Slide 82
T852f183, T852f185

Fuel Pump The in-tank fuel pump on all models draws fuel from the storage tank
and delivers it to the injection system. The fuel pump’s pumping capacity

is designed to exceed engine requirements. This ensures that there will
always be enough fuel to meet engine demands.
In-Tank Electric

An electric fuel pump is mounted in the tank and immersed in fuel.
The fuel cools and lubricates the pump. When the pump is turned ON,
it draws fuel in through a filtered inlet and discharges pressurized fuel
through the outlet port.
An outlet check valve in the discharge outlet maintains a residual pressure
in the system when the engine is OFF. This has two benefits:
•Improved starting characteristics — without residual fuel pressure,
the system would have to be pressurized each time the engine was
started. This would increase engine starting (cranking) time.

•Reduced chance of vapor lock — when a hot engine is shut off,
fuel temperature in the lines around the engine increases. Keeping
the system pressurized raises the boiling point of the fuel and helps
prevent the fuel from vaporizing.
A pressure relief valve will open if the fuel system becomes restricted.
This safety device prevents excess pressure from rupturing fuel lines or
damaging the pump.

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Fuel Pump: Jet Pump

Fuel Systems

Slide 83
036EG70TE , 036EG39TE

Jet Pump

Some models use a jet pump in addition to the standard in-tank electric
pump. This saddle tank design accommodates the propeller shaft.
A saddle tank tends to cause fuel to be present in both chamber A and
chamber B when the fuel level is low. To prevent this from occurring, the
jet pump transfers the fuel from chamber B to chamber A. The pressure
difference created by the fuel as it passes through the venturi is used to
draw the fuel out of chamber B and send it to chamber A.

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Fuel Pump Controls: ECM ON/OFF

Fuel Systems

Slide 84
G43045

Fuel Pump Controls The most accurate way to determine the type of fuel control circuit is
to look it up in the appropriate Repair Manual or EWD. Basic methods

include:
•ON/OFF control by the ECM.

•Multiple speed control with Fuel Pump ECU: Larger displacement
engines require a higher volume of fuel during starting and
heavy load conditions. A high capacity fuel pump can meet the
demand but may also produce excessive noise and consume more
power. Multiple speed fuel pump control can help overcome the
disadvantages and increase pump life.
The following descriptions are typical; not all systems will have exactly
the components shown.
ON/OFF Control
by the ECM

The ECM controls the fuel pump based on engine operating conditions:

•Engine start: During cranking, current from the ignition switch to
the starter relay (ST) coil turns the relay ON. Current also flows
from the ignition switch to the STA terminal of the ECM. When the
STA signal and the crankshaft position signal (NE) are input to the
ECM, Tr is turned ON, current travels through the coil of the circuit
opening relay (C/OPN), the relay switches ON, power is supplied to
the fuel pump and the pump operates.
•Engine running: Once the engine is running, the ECM continues to
receive the NE signal and keeps the fuel pump ON.
•Engine stopped: When the engine stops, the NE signal stops and
the ECM turns Tr OFF, allowing the C/OPN relay to open, causing
the fuel pump to lose power and stop running as well.

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Fuel Systems

Fuel Pump Controls: 2-Speed with Resistor

Slide 85

2-Speed Control
with Resistor
Low Speed Operation

High Speed Operation

ON-OFF and speed control of the fuel pump is controlled with a resistor
based on signals from the ECM.
When the engine is idling and under normal driving conditions (when
a small amount of fuel is required), the ECM turns ON the fuel pump
control relay. The relay switches to contact B, sending current through the
resistor. This reduces the available current and voltage to the fuel pump,
causing it to run at low speed.
When the engine is operating at high speeds or under heavy load, the
ECM turns OFF the fuel pump control relay. The relay switches to contact
A and the current to the fuel pump flows directly to the pump, bypassing
the resistor. This causes the fuel pump to run at high speed. The fuel
pump also runs at high speed while the engine is starting.

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Fuel Pump Controls: 3-Speed Control with Fuel Pump ECU

Fuel Systems

Slide 86
T852f139/T852f194

3-Speed Control
with Fuel Pump ECU

In this system, the Fuel Pump ECU varies supply voltage to create three
fuel pump speeds (high, medium, and low):

•High speed: During starting and heavy load conditions, the ECM
sends a HI signal (about 5 volts) to the Fuel Pump ECU. The ECU
then supplies full battery power to the fuel pump.

•Medium speed: Under heavy loads at low speed, the ECM sends a
pulsewidth modulated 2.5 volt signal to the Fuel Pump ECU. The
ECU then applies about 10 volts to the fuel pump to operate it at
medium speed.
•Low speed: When idling or under light loads, the ECM sends a
pulsewidth modulated 1.3 volt signal to the Fuel Pump ECU. The
ECU then applies 8.5 volts to the fuel pump, lowering operating

noise and reducing power consumption.

•OFF: When the engine is stopped or stalls and when SRS
deployment occurs, the ECM sends 0 volts to the Fuel Pump ECU
to stop the fuel pump.

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Fuel Pump Interruption

Fuel Systems

Slide 87
T852f196/T852f197

Fuel Pump The fuel pump is shut off in certain types of collisions. There are two
Interruption methods for shutting off the fuel pump: ECM controlled and mechanical
inertia switch.
ECM Controlled

Inertia Switch

Most late model vehicles shut off the fuel pump when any of the SRS
airbags deploy. When the ECM receives a deployment signal from the
Airbag Sensor Assembly, the ECM turns OFF the Circuit Opening Relay.
Cycle the ignition switch to cancel fuel pump shutoff and restart the engine.
An inertia switch is found on Land Cruiser from 1998 to 2002 model years.

It includes a switch to shut OFF the fuel pump when the vehicle is involved
in a collision to minimize fuel leakage. Electrically, the fuel pump inertia
switch is located between the ECM and Fuel Pump ECU.
The inertia switch consists of a ball, spring loaded link, contact point, and
reset switch. If the force of a collision is greater than a predetermined value,
the ball will move and the spring loaded link will drop, opening the contact
point. This opens the circuit between the ECM and Fuel Pump ECU, and
the fuel pump turns OFF.
If the fuel pump inertia switch has tripped, reset it by pushing up on the
reset switch for at least one second.

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Vacuum Pressure Regulator

Fuel Systems

Slide
Slide88
1
T874f509, T874f310,
T852f201/T852f202
T874f508

Fuel Pressure Fuel pressure must be regulated to ensure proper operation of the fuel

Regulators injection system. Although there are different types, all fuel pressure
regulators maintain fuel pressure within a specified range so that it does not
go too high or too low.
Vacuum Modulated
Pressure Regulator

The vacuum modulated pressure regulator maintains a constant pressure
differential across the fuel injectors. This means that fuel rail pressure will
always be at a constant value above manifold absolute pressure.
Low intake manifold pressure (for example, at idle) pulls on the diaphragm,
decreasing spring pressure. This allows more fuel to return to the fuel tank,
decreasing pressure in the fuel rail. Opening the throttle increases manifold
pressure. With less vacuum on the diaphragm spring, pressure will increase,
restricting fuel flow to the fuel tank. This increases pressure in the fuel rail.

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Fuel Systems

Atmospheric Modulated Pressure Regulator

Slide
Slide89
1
T874f509, T874f310, T852f202
T874f508

Atmospheric Modulated
Pressure Regulator

The atmospheric modulated pressure regulator changes fuel pressure in
relationship to atmospheric pressure. A hose is connected from the pressure
regulator to the air intake hose between the air filter and throttle plate.
A combination of spring pressure and atmospheric pressure determines
fuel pressure. One example is a climb from low to high elevation, where
a decrease in atmospheric pressure on the diaphragm results in lower fuel
pressure.

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Fixed (Constant) Pressure Regulator

Fuel Systems

Slide
Slide90
1
T874f509, T874f310, T852f203
T874f508

Fixed (Constant)
Pressure Regulator

Returnless fuel delivery systems use a constant pressure regulator located
in the fuel pump assembly inside the fuel tank. This type of regulator
maintains a constant fuel pressure regardless of intake manifold or
atmospheric pressure. Fuel pressure is determined by the force of the
spring inside the regulator. When pressure from the fuel pump overcomes
spring pressure, excess fuel is bypassed into the fuel tank.
Fixed pressure fuel systems typically maintain a higher fuel pressure than
vacuum or atmospheric modulated systems.

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Fuel Pressure Diagnosis

Fuel Systems

Slide
Slide91
1
T874f509, T874f310, T874f604
T874f508

Fuel Pressure Diagnosis

A pressure gauge is used to obtain accurate fuel pressure readings.
•If the pressure is too high, check the fuel pressure regulator.

•If the pressure is too low, check the fuel hoses, fuel pump, fuel
filter, and pressure regulator.
In addition to checking fuel pressure with the engine running, it is also
important to check residual fuel pressure after the engine is OFF.

•Fuel pressure should remain stable at 21 psi for at least 5 minutes
after the engine is stopped.

•If fuel pressure drops below specification, check the fuel pump, fuel
pressure regulator, fuel pump outlet check valve, and fuel injectors.
It is important to dissipate fuel pressure prior to performing service or
repairs on the fuel system.
•Remove the EFI relay or Circuit Opening Relay.

•Start the vehicle and allow it to run until the engine stalls.
NOTE: Always inspect fuel lines and connectors for damage prior to reassembly.

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Fuel Delivery Lines and Connectors

Fuel Systems

Slide 92
T852f206/T852f207/T852f208/T852f209/T852f210/285EG38

Fuel Delivery A variety of materials and connectors are used within the fuel system.
Components Steel and synthetic materials are used, depending on component location
and vehicle model. It is critical that the correct procedures be followed
when servicing the fuel lines and related components. Inspect all tabs for
damage, and replace any found.
Lines and Connectors
Fuel Tank

82

Port injection system connectors may be the threaded type or the quick
connector type.
The fuel tank is designed to safely contain the fuel and evaporative
emissions. Typically, it houses the fuel pump assembly and rollover
protection valves (if applicable).

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Fuel Filters

Fuel Systems

Slide 93
T852f211/T852f212

Fuel Filters

Typically, there are two fuel filters in the fuel delivery system:

•The first filter is located on the suction side of the fuel pump. This
filter prevents debris from damaging the fuel pump.

•The second filter is located between the pump and fuel rail to
remove dirt and contaminants from the fuel before it is delivered to
the injectors. The injectors require extremely clean fuel, so this filter
removes extremely small particles from the fuel. The second filter
may be part of the in-tank fuel pump assembly or outside the tank
in the fuel line leading to the fuel rail.
Filters are designed to be maintenance-free with no required service
replacement. However, a restricted fuel filter may prevent the proper fuel
pressure from reaching the injectors. A restricted fuel filter may cause
hard start, surge, low power under load, etc. A completely clogged filter
can prevent the engine from starting.

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Pulsation Damper

Fuel Systems

Slide 94
T852f213/T852f214

Pulsation Damper

Fluctuating fuel pressure can cause more or less than the desired amount
of fuel to be injected. Pulsation dampers help absorb changes in fuel
pressure caused by the rapid opening and closing of the fuel injectors.
Different fuel system designs feature different damper designs:

•Port injection system: If used, the pulsation damper is mounted
on the fuel rail. When pressure begins to increase, the spring
loaded diaphragm retracts slightly, increasing fuel rail volume.
This momentarily prevents fuel pressure from becoming too high.
When pressure begins to drop, the spring loaded diaphragm extends,
slightly reducing effective fuel rail volume. This momentarily
prevents fuel pressure from becoming too low. The screw mounted
at the top of the damper provides an easy check for fuel system
pressure. When the screw is up, the fuel rail is pressurized. Under
most conditions, this check is not adequate. The screw is not
adjustable (it is used to calibrate the damper at the factory).
•Inner pipe pulsation damper: Some late model fuel injection
systems use an inner pipe style pulsation damper. This eliminates
the use of a separate pulsation damper, making the fuel system more
compact and lightweight. This damper consists of a hollow inner
pipe inside the fuel delivery pipe. When fuel pressure fluctuates, the
shape of the inner pipe changes with the pulsation, thus changing
the internal capacity of the delivery pipe. This change in capacity
absorbs the fuel pulsations.

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Port Fuel Injection Operation

Fuel Systems

Slide
Slide96
1
T874f509,
T852f217/T852f218/T852f818
T874f310, T874f508

Port Fuel Injection The fuel injector, when turned ON by the ECM, atomizes and directs fuel
Operation into the intake manifold. There is one injector per cylinder mounted in the
intake manifold before the intake valve(s).
Fuel Injectors

Injectors are installed with an insulator/seal on the manifold end to
insulate them from heat and prevent atmospheric pressure from leaking
into the manifold. The fuel delivery pipe secures the injector. An O-ring
between the delivery pipe and injector prevents fuel from leaking.
When replacing an injector it is critical that the correct injector be used.
Different engines require different injectors. Injectors are designed to flow
a specified amount of fuel when open. In addition, the number of holes at
the tip of the injector varies with engine and model year.
Inside the injector is a solenoid and needle valve. The fuel injector circuit
is usually a ground switched circuit. To turn ON the injector, the ECM
completes a path to ground. The magnetic field pulls the needle valve up
against spring pressure and fuel flows out of the injector. When the ECM

turns OFF the circuit, spring pressure forces the needle valve onto its seat
and shuts off fuel flow.

NOTE: Confirm part numbers and resistance values before installing new fuel

injectors. Fuel injectors for one model may fit on another model, but
could have different resistance values. Installing an injector with the
wrong resistance value may cause a no-start condition, driveability
concerns, or ECM failure.

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Fuel Cut

Fuel Systems

Slide
Slide97
1
T874f509, T874f310, T852f229
T874f508

Fuel Cut The ECM controls fuel delivery differently according to engine and
vehicle operating conditions:

•Deceleration fuel cut: During closed throttle deceleration at
moderate to high engine speeds, fuel delivery is not necessary or
desirable. To prevent excessive deceleration emissions and improve
fuel economy, the ECM will not open the injectors under certain
deceleration conditions. The ECM will resume fuel injection at a
calculated RPM. Referring to the graph, fuel cutoff and resumption
speeds are variable, depending on coolant temperature, A/C
compressor clutch status, and the STP signal. Essentially, when
extra engine loads are present, the ECM will begin fuel injection
earlier.
•Fuel Tau cut: A mode employed on some engines during long
deceleration times with the throttle valve closed. During these
times, excess air, without the presence of fuel, cools the catalytic
converter, reducing its efficiency. To prevent this, the ECM very
briefly pulses the injectors.

•Engine over-rev fuel cutoff: To prevent engine damage, a revlimiter is programmed into the ECM. Any time the engine RPM
exceeds the pre-programmed threshold, the ECM shuts off the
injectors. Once RPM falls below the threshold, the injectors are
turned back ON. Typically, the threshold RPM is slightly above the
engine’s redline RPM.

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•Vehicle over-speed fuel cutoff: On some vehicles, fuel injection
is halted if the vehicle speed exceeds a predetermined threshold
programmed into the ECM. Fuel injection resumes after the speed
drops below this threshold.

Open and Closed Loop Operation

Fuel Systems

Slide 1

T874f509, T874f310,Slide
T874f508
98

Open and Closed An open loop system does not monitor its output nor make adjustments
Loop Operation based on its output. An example of an open loop system is vehicle climate
control (without automatic air conditioning).
A system that controls its output by monitoring its output is called a
closed loop system. For example, the vehicle’s cruise control system
adjusts vehicle speed by monitoring vehicle speed. If speed is too low,
the system responds by increasing vehicle speed. When the ECM corrects
the air/fuel ratio based on O2 or A/F sensors, the system is said to be in
closed loop.
Other examples of closed loop systems include:
•Voltage regulation

•Ignition system knock control

•Closed loop air/fuel ratio correction control

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Open Loop Mode

Fuel Systems

Slide
Slide99
1
T874f509, T874f310, T852f234
T874f508

Open Loop Mode

The ECM will be in open loop mode during:
•Engine start

•Low O2 or A/F sensor operating temperature
•Fuel cutoff

•Wide open throttle (WOT)
If the engine will not go into closed loop mode, the problem may be no
response from O2 or A/F sensors or a malfunction in the heater circuit.
Usually, no response from O2 or A/F sensors will set a DTC.
If there is a driveability problem that only occurs in closed loop, a fault in
O2 or A/F sensor circuits or anything that disrupts the air/fuel ratio may
be the cause.

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Fuel Systems

Closed Loop Mode

Slide
Slide
100
1
T874f509, T874f310, T852f235
T874f508

Closed Loop Mode
(O2 Sensor)

When in closed loop, the ECM uses the O2 sensor voltage signal to
make minor corrections to the injection duration. This is done to help the
catalytic converter operate at peak efficiency.
When the voltage is higher than 450 mV, the air/fuel ratio is judged to
be richer than the ideal air/fuel ratio, and the amount of fuel injected is
reduced at a constant rate. The reduction in the duration continues until
the O2 sensor signal switches to a low voltage (lean air/fuel ratio).
When the voltage signal is lower than 450 mV, the air/fuel ratio is judged
to be leaner than the ideal air/fuel ratio so the amount of fuel injected
is increased at a constant rate. The increase in duration continues until

the O2 sensor switches to high voltage (rich air/fuel ratio). At this point,
the ECM will slowly decrease the amount of fuel injected, therefore the
air/fuel ratio oscillates slightly richer or leaner than the ideal air/fuel
ratio. The result is an average air/fuel ratio of approximately 14.7:1.
This produces the proper mixture of exhaust gases so that the catalytic
converter operates at its most efficient level.
O2 sensor signal voltage abruptly changes at the ideal air/fuel ratio, and
changes very little as the air/fuel ratio extends beyond ideal. Because
the ECM changes injection duration in gradual steps until the O2 sensor
signal abruptly switches, fuel control is less precise than with an A/F
sensor.

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Closed Loop Mode, cont.

Closed Loop Mode
(A/F Sensor)

Fuel Systems

With an A/F sensor, air/fuel mixture correction is faster and more precise.
The A/F sensor outputs a voltage signal that is relatively proportional to
the air/fuel ratio. The ECM then knows how much the air/fuel ratio has
deviated from the ideal, and the ECM can immediately adjust the fuel

injection duration. This rapid correction reduces emission levels because
the ECM can more accurately maintain the ideal air/fuel ratio for catalytic
converter efficiency.
Therefore, when observing A/F sensor voltage output, the output is
relatively constant because there is no cycling between rich and lean.

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Fuel Trim

Fuel Systems

Slide 1

T874f509, T874f310,
Slide
T874f508
102

Fuel Trim As the engine and sensors change over time, the ECM needs to adjust fuel
injection duration for improved driveability and emission performance. Fuel
trim is a program in the ECM that allows it to compensate for these changes.
If the fuel trim value is positive, the ECM concluded that the engine was
running lean based on exhaust sensor readings and increased the injection
duration to correct the lean mixture. If the fuel trim value is negative,
the ECM concluded that the engine was running rich and decreased the
injection duration to correct the rich mixture.

•The short-term fuel trim value is the immediate amount of
correction the ECM is making when it is in closed-loop fuel control.
•The long-term fuel trim value is a learned value that is based on
the short-term fuel trim correction. Long-term fuel trim is part of the
engine’s basic injection calculation and is applied during both open
and closed loop operation. The ECM will learn different long-term
fuel trim values for different engine conditions — the engine may
require a different amount of correction depending on load and RPM.

Combined fuel compensation is the sum of short-term fuel trim and longterm fuel trim. Techstream displays the current short-term and long-term
fuel trim percentages, as well as a total fuel trim number. Long-term
fuel trim is stored in the ECM’s memory until power is disconnected for
several minutes.
NOTE: Abnormal fuel trim values do not necessarily mean the engine is actually

running rich or lean. Changes in fuel trim mean the ECM had to make
corrections to get the engine to run properly.
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Fuel Injection Signal

Fuel Systems

Slide 1

T874f509, T874f310,
Slide
T874f508
103

Fuel Injection Signal Injection duration, when the injector is turned on and off, can be seen on
the oscilloscope wave pattern.

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Fuel System Diagnosis

Fuel Systems

Slide 104

Fuel System When trying to determine the cause of a fuel system concern, use
Diagnosis Techstream to check the Freeze Frame data and attempt to duplicate
the conditions. Use the Technical Information System (TIS) for Repair
Manual (RM) and Electrical Wiring Diagram (EWD) information, and
look for applicable Technical Service Bulletins (TSBs).
Fuel Trim

When trying to determine the cause of a fuel trim issue, the most
important aspect of diagnosis is to match what the Techstream is reporting
to the engine’s actual running condition. For example, black spark plugs

coupled with positive fuel trims may indicate a feedback issue. Verify that
the fuel trims are currently abnormal. When diagnosing an intermittent
condition, check the Freeze Frame data and duplicate the conditions.
Investigate other DTCs and troubleshoot them first.
Abnormal cylinder compression, fuel pressure, wrong fuel, spark plug
condition, etc., will affect fuel trim. On multiple-bank engines, if fuel trim
is significantly different between banks, concentrate on things affecting
only one bank, such as valve timing, O2 and A/F sensors, or mechanical
issues. Most types of vacuum leaks or a contaminated MAF sensor will
not usually cause an issue on just one bank.

NOTE: Combined fuel trim is not the same as Total FT on the Techstream Data

List. Combined fuel trim is the sum of Short FT and Long FT for each
bank. Total FT is an ECM interpretation of the air/fuel mixture.

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