toyota training course t874 engine control systems II ch07

• Feed fuel pump draws fuel from the tank under control of Fuel Pump ECU in certain port injection systems.. Some port injection systems use return type delivery.In a return type port in

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.Most port fuel injection systems have the following 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.

Fuel Systems

Typical Port Injection

Components

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

Return Type Fuel Delivery

Slide 80

T852f181

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

Returnless Type Fuel

Delivery

Slide 81

208EG117

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

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

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

Jet Pump

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036EG70TE , 036EG39TE

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

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

Fuel Pump Controls

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

2-Speed Control

with Resistor

Low Speed Operation

High Speed Operation

Slide 85

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

3-Speed Control

with Fuel Pump ECU

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

Slide 86

T852f139/T852f194

The fuel pump is shut off in certain types of collisions There are two methods for shutting off the fuel pump: ECM controlled and mechanical 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

Fuel Pump Interruption

Slide 1

T874f509, T874f310, T874f508

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

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

Slide 1

T874f509, T874f310, T874f508

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

Slide 1

T874f509, T874f310, T874f508

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

Slide 1

T874f509, T874f310, T874f508

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

Always inspect fuel lines and connectors for damage prior to reassembly

Fuel Pressure Diagnosis

A variety of materials and connectors are used within the fuel system 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.

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)

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

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

Pulsation Damper

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T852f213/T852f214

Slide 1

T874f509, T874f310, T874f508

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

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

Confirm part numbers and resistance values before installing new fuel

Port Fuel Injection