Lexus SC300 / Lexus SC400. Manual - part 501

The EFI system is composed of three basic sub–systems: Fuel, Air Induction and Electronic Control

Systems.

FUEL SYSTEM

An electric pump fuel pressure supplies sufficient fuel, under a constant pressure, to the EFI injectors. In

accordance with signals from the ECU (Electronic Control Unit), these injectors inject the quantity of fuel most
appropriate for the engine condition into the intake manifold.

AIR INDUCTION SYSTEM

The air induction system provides sufficient air for engine operation.

ELECTRONIC CONTROL SYSTEM

The 1UZ–FE engine (ECU–formerly EFI computer) with a microcomputer centrally controls the EFI, ESA,

ISC and Diagnosis system, etc.

The ECU controls the following functions:

1. 

Electronic Fuel Injection (EFI)

The ECU receives signals from various sensors indicating changing engine operation conditions such as:

Intake air volume
Intake air temperature
Coolant temperature
Engine rpm
Acceleration/deceleration
Exhaust oxygen content etc.

The signals are utilized by the ECU to determine the injection duration necessary for an optimum air–fuel
ratio.

2. 

Electronic Spark Advance (ESA)
The ECU is programmed with data for optimum ignition timing under any and all operating conditions. Using
data provided by sensors which monitor various engine functions (rpm, coolant temperature, etc.), the
Electronic Control Unit (ECU) triggers the spark at precisely right instant. (See IG section)

3. 

Idle Speed Control (ISC)
The ECU is programmed with idle speed data for various engine conditions (coolant temperature, air condi-
tioner ON/OFF, etc.).
The air volume flowing through the throttle valve by–pass passage is adjusted according to the signal from
each sensor and the idle speed is kept at the set value.

4. Diagnosis 

Function

When the ECU detects any malfunctions or abnormalities in the sensor network, it lights the ”CHECK” en-
gine warning light in the combination meter. At the same time, the trouble is identified and a diagnostic code
is recorded by the ECU. The diagnostic code can be read by the number of blinks of the ”CHECK” engine
warning light when terminals TE1 and E1 are connected. The diagnostic codes are refer to the later page.
(See TR section)

5. Self–Correction 

Function

If any sensor malfunctions, an average value recorded in the back–up circuit is substituted to make driving
possible.
If danger is predicted, the engine is stopped and the ”CHECK” engine warning light will light up.

6. Fail–Safe 

Function

Even if an abnormality occurs in the ECU, the back–up circuit uses a specified fuel injection and ignition
timing to provide vehicle driveability, and also lightsup the ”CHECK” engine warning light.

FI–4

EFI SYSTEM   –   Description

OPERATION

FI–4

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EFI SYSTEM

  

Operation

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EFI SYSTEM

Operation

FI–5

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.

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

284 kPa (2.9 kgf/cm2, 41 psi) higher than the pressure inside the intake manifold, and excess fuel is returned
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.

FI–6

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EFI SYSTEM

Operation