Copyright by Goodheart-Willcox Co., Inc.
Chapter 16 Turbocharging and Supercharging Systems 333
Vacuum control
solenoid for
waste gate valve
Vacuum control solenoid
for exhaust gas
control valve
Exhaust gas
control valve
Vacuum control
solenoid for exhaust
bypass valve
No. 2
turbocharger
Intake air
control valve
Vacuum control
solenoid for intake
air control valve
Pressure
tank
Throttle valve
Exhaust bypass valve
Waste gate
valve
Inter-
cooler
No. 1
turbocharger
Air
cleaner
Cool compressed air
Uncompressed air
Hot compressed air
Exhaust
Figure 16-8. A sequential turbocharger system contains two turbochargers. One turbocharger operates at low engine speeds. Both
turbochargers operate at high engine speed. (Toyota)
gasses are much cooler and will help prevent heat
damage as the unit cools. Idling may also prevent
oil starvation damage by allowing the turbo to slow
down before the engine and oil supply stop.
A turbo timer is a device that keeps the engine
running for a cooldown period after the ignition key has
been shut off. It is an electronic circuit that includes the
ignition and computer control circuits. When the driver
shuts off the ignition, the turbo timer keeps the engine
idling to provide time for the engine and turbo to cool off.
Then, the circuit automatically shuts the engine off.
Checking the Turbocharging System
There are several checks that can be made to deter-
mine the condition of the turbocharging system. These
include:
Checking all vacuum lines to the waste gate and oil
lines to the turbocharger for proper connection.
Using regulated, low-pressure air to check for waste
gate diaphragm leakage and operation.
Using a dash gauge or a test gauge to measure boost
pressure. If needed, connect the pressure gauge to an
intake manifold fitting.
Using a stethoscope to listen for bad turbocharger
bearings.
Servicing a Turbocharger
Checking the condition of the inside of the turbo-
charger requires removing the turbocharger from the
engine. Removal procedures may vary by manufacturer,
so refer to the service manual for specific instructions.
However, the basic steps are:
1. Remove the air cleaner.
2. Remove the turbocharger heat shield.
3. Remove the exhaust outlet pipe and exhaust down
pipe.
4. Remove the boost control tube.
5. Remove the oil supply line.