Lexus ES300 (1997 year). Service manual — part 8

31

ENGINE — 1MZ-FE ENGINE

COOLING SYSTEM

1. Cooling Fan System

The cooling system has been changed from the previous electronically controlled hydraulic cooling fan
system to an electric cooling fan system.

The cooling fan controls the fan speed in 3 steps (OFF, Low, High) by using the 2 water temperature switches
in accordance with the water temperature and the operating condition of the air conditioner and by turning
the 3 fan relays ON and OFF and connecting 2 fan motors in a series or parallel circuit.

Wiring Diagram

Cooling Fan Operation

Water Temperatue

90

o

C (194

o

F) or

lower

90

o

C (194

o

F)

~95

o

C (203

o

F)

95

o

C (203

o

F) or

higher

Water Temperature Switch

No. 1

ON

ON

OFF

Water Temperature Switch

No. 2

OFF

ON

ON

A/C Condition

OFF

ON

ON

A/C OFF

OFF

LOW

HIGH

A/C ON

Pressure Switch ON

LOW

LOW

HIGH

A/C ON

Pressure Switch OFF

HIGH

HIGH

HIGH

32

ENGINE — 1MZ-FE ENGINE

INTAKE AND EXHAUST SYSTEM

1. 2-Way Exhaust Control System

A 2-way exhaust control system is used. This system reduces the back pressure by opening and closing
a variable valve that is enclosed in the main muffler, thus varying the exhaust gas passage.

The valve opens steplessly in accordance with the operating condition of the engine, thus enabling a
quieter operation at lower engine speeds, and reducing back pressure at higher engine speeds.

Construction

1) Control Valve

The control valve is enclosed in the main
muffler. When the exhaust gas pressure
overcomes the spring pressure, the control
valve opens steplessly in accordance with the
exhaust gas pressure.

Operation

1) When Control Valve is Closed (low engine speed)

Since the pressure in the main muffler is low, the control valve is closed. Hence exhaust gas does not pass
the bypass passage, and exhaust noise is decreased by the main muffler.

2) When Control Valve is Opened (middle to high engine speed)

The valve opens more as the engine speed and the back pressure in the muffler increase. This allows a
large volume of exhaust gas to pass the bypass passage thereby substantially decreasing the back
pressure.

33

ENGINE — 1MZ-FE ENGINE

FUEL SYSTEM

1. Fuel Returnless System

The new ES300 has adopted a fuel returnless system to reduce evaporative emissions. With the pressure
regulator housed inside the fuel tank, this system eliminates the return of fuel from the engine area. This
prevents the internal temperature of the fuel tank from rising, and reduces evaporative emissions.

ENGINE MOUNTING

1. General

The internal orifice of the front mount has been modified to improve the tiding comfort and to ensure a
quieter operation at idling.

The characteristics of the rear mount, left mount, torque rod, and absorber have been optimized.

34

ENGINE — 1MZ-FE ENGINE

ENGINE CONTROL SYSTEM

1. General

The engine control system of the new 1MZ-FE engine is basically the same in construction and operation
as that of the previous 1MZ-FE engine. However, the fuel pressure control has been discontinued and the
EGR control system has been changed.
The engine control system of the new 1MZ-FE engine and previous 1MZ-FE engine are compared below.

System

Outline

New

Previous

EFI

(Sequential

An L-type SFI system directly detects the intake air
mass with a hot wire type mass air flow meter.

(Sequential
Multiport Fuel
Injection)

The fuel injection system is a sequential multiport fuel
rejection system.

ESA

Ignition timing is determined by the ECM based on
signals from various sensors. The ECM corrects
ignition timing in response to engine knocking.

ESA
(Electronic Spark
Advance)

2 knock sensors are used to improve knock detection.

Advance)

Torque control correction during gear shifting has
been used to minimize the shift shock.

IAC

(idle Air Control)

A rotary solenoid type IAC valve controls the fast idle
and idle speeds.

ACIS

(Acoustic Control
Induction System)

The intake air passages are switched according to the
engine speed and throttle valve angle to increase
performance in all speed ranges.

Fuel Pressure
Control

In hot engine conditions, the fuel pressure is
increased to improve restartability.

Oxygen Sensor
Heater Control

Maintains the temperature of the oxygen sensors at an
appropriate level to increase accuracy of detection of
the oxygen concentration in the exhaust gas.

EGR
Cut-Off Control

Cuts off EGR according to the engine condition to
maintain drivability of the vehicle and durability of the
EGR components.

EGR Control

Uses the duty control type VSV and EGR valve
position sensor, controlling the EGR volume in
accordance with the engine condition.

Evaporative
Emission Control

The ECM controls the purge flow of evaporative
emissions (HC) in the charcoal canister in accordance
with engine conditions.

When the ECM detects a malfunction, the ECM
diagnoses and memorizes the failed section.

Diagnosis

The diagnosis system includes a function that detects
a malfunction in the evaporative emission control
system.

Fail-Safe

When the ECM detects a malfunction, the ECM stops
or controls the engine according to the data already
stored in memory.