Lexus SC300 / Lexus SC400. Manual — part 503

FUEL SYSTEM

Fuel is pumped up by the fuel pump, which flows through the fuel filter under pressure through the fuel pipe

to the delivery pipe where it is distributed to each injector and the cold start injector.

The fuel pressure regulator adjusts the pressure of the fuel from the fuel line (high pressure side) to a pres-

sure 284 kPa (2.9 kgf/cm

2

, 41 psi) higher than the pressure inside the intake manifold, and excess fuel is re-

turned to the fuel tank through the return pipe.

When the engine is hot, the fuel pressure is increased to control percolation in the fuel system and improve

restartability and idling stability.

The pulsation damper absorbs the slight fluctuations in fuel pressure caused by the injector.

The injectors operate on input of injection signals from the ECU and inject fuel into the intake manifold.

The cold start injector operates when starting with low coolant temperature or at normal temperature

ranges, injecting fuel into the air intake chamber to improve startability.

FI–7

EFI SYSTEM – Operation

AIR INDUCTION SYSTEM

Air filtered through the air cleaner passes through the air flow meter and the amount flowing to the air intake

chamber is determined according to the throttle valve opening in the throttle body and the engine rpm.

Air flow meter measures the air intake flow to the engine by the swirl frequency.
Located in the throttle body is the throttle valve, which regulates the volume of air intake to the engine. Air

intake controlled by the throttle valve opening is distributed from the intake chamber to the manifold of each
cylinder and is drain into the combustion chamber.

At air low temperature the ISC valve opens and the air flows through the ISC valve, as well as the throttle

body, into the air intake chamber. During engine warming up, even if the throttle valve is completely closed, air
flows to the air intake chamber, thereby increasing the idle speed (first idle operation).

The air intake chamber prevents pulsation of the intake air, reduces the influence on the air flow meter and

increases the air intake volume. It also prevents intake air interference in each cylinder.

FI–8

EFI SYSTEM – Operation

ELECTRONIC CONTROL SYSTEM

The control system consists of sensors which detect various engine conditions, and a ECU which deter-

mines the injection volume (timing) based on the signals from the sensors.

The various sensors detect the air intake volume, engine rpm, oxygen density in the exhaust gas, coolant

temperature, air intake temperature and atmospheric pressure etc. and convert the information into an electrical
signal which is sent to the ECU. Based on these signals, the ECU calculates the optimum ignition timing for the
current conditions and operates the injectors.

The ECU not only controls the fuel injection timing, but also the self diagnostic function which records the

occurrence of a malfunction, ignition timing control, idle rpm control, EGR control, EVAP control, fuel pressure
control and fuel pump control.

FI–9

EFI SYSTEM – Operation

PREPARATION

SST (SPECIAL SERVICE TOOLS)

Illustration

Part No.

Part Name

Note

09268–41045

Injection Measuring
Tool Set

(09268–41090)

(No. 7 Union)

Injector

(09268–52010)

(Injection Measuring
Attachment)

Injector

(09405–09015)

(No. 1 Union)

Injector

09268–45012

EFI Fuel Pressure
Gauge

09612–24014

Steering Gear
Housing Overhaul
Tool Set

(09617–24011

(Steering Rack Wrench)

Fuel pressure pulsation damper

09631–22020

Power Steering
Hose Nut 14 x 17 mm
Wrench Set

Fuel line flare nut

09816–30010

Oil Pressure
Switch Socket

Knock sensor

09842–30070

Wire “F”
EFI Inspection

Injector

09843–18020

Diagnosis Check
Wire

09990–01000

Engine Control
Computer Check
Harness “A”

–

EFI SYSTEM

Preparation

FI–9