Copyright by Goodheart-Willcox Co., Inc.
Chapter 16 Turbocharging and Supercharging Systems 341
Figure 16-18. Using a pressure gauge to measure boost pressure.
Figure 16-19. Use a hand-held vacuum pump to check for
proper action of the bypass diaphragm.
Figure 16-20. Checking for a proper electrical signal to the
vacuum solenoid. When the accelerator pedal is pushed to
the floor, battery voltage should be present at the vacuum
solenoid.
Measuring Supercharger Boost Pressure
Install a pressure gauge to measure actual boost pres-
sure, Figure 16-18. Refer to the manufacturer’s service
information for the correct connection point. Compare
actual boost pressure to specifications for the engine
speed. If boost is low, check the pressure regulator circuit
or check for internal rotor or housing damage.
Low Boost
When a supercharged engine fails to generate proper
boost pressure, it is often due to:
A broken or slipping drive belt.
An inoperative electromagnetic drive pulley mechanism.
An inoperative pressure bypass valve system.
Physical wear or damage inside the supercharger.
A badly clogged air filter or an obstruction in the air
intake.
If there is low or no boost pressure, make sure
the electromagnetic clutch is engaging if the vehicle is
equipped with one. Also, make sure the supercharger is
spinning. If the supercharger is spinning, check for loose or
disconnected vacuum lines to the bypass valve.
To check the operation of the bypass valve, apply
vacuum to the diaphragm. See Figure 16-19. Make sure
the level or arm on the bypass valve moves as vacuum is
applied.
If the bypass valve diaphragm is good but the bypass
valve is not working, check the vacuum solenoid that con-
trols vacuum to the bypass diaphragm. Make sure the ECM
is sending a proper signal to the solenoid, Figure 16-20.
Overboost
If a supercharged engine has too much boost, or
overboost, the engine may seem to have more power than
normal, accelerate (rev up) too quickly, and detonate or
knock under high-load conditions. Too much supercharger
boost can be caused by a bypass valve stuck closed, often
due to carbon buildup or a mechanical problem. An
electronic control problem or engine modification may
also lead to overboost.
Intercooler Service
Problems with the intercooler system are similar to the
problems that develop in the engine cooling system. Some
possible problems include an inoperative pump, deterio-
rated coolant, leaking intercooler radiator or intercooler,
and leaking hoses or lines.
During service, check the level and condition of the
coolant in the intercooler reservoir. This reservoir is usually
located on the side of the intercooler radiator or engine
compartment. See Figure 16-21A.