Mityvac MV8500 silverline elite aUtoMotive test kit - Manual (Page 12)

Page Number - 1 Form 8433
SYSTEM OPERATION
The turbocharger wastegate (exhaust bypass valve)
limits the amount of boost (intake manifold pres-
sure) created by the turbo . When intake manifold
pressure becomes too high, the wastegate opens
to allow some exhaust to bypass the turbo . This
reduces the turbo boost .
Most turbo wastegate actuators operate using a
mechanical spring and diaphragm design . Under
normal operating conditions, the spring holds the
wastegate valve closed, and all exhaust is directed
to the turbocharger . A small tube connects the
wastegate actuator to the intake manifold or turbo
air outlet . When boost pressure becomes too high, it
pushes against the diaphragm until it overcomes the
spring force, causing the wastegate to open .
Testing the function of the wastegate and wastegate
actuator involves attaching the Mityvac hand pump
to wastegate and applying pressure .
SERVICE PROCEDURES
Follow the procedures below to diagnose a turbo- or
super-charger wastegate and actuator:
Cold Test for Visual Movement
1) Locate the wastegate actuator, and inspect it for
damage . Check the pressure hose for visible leaks
or cracks . Replace if necessary .
) Disconnect the pressure hose from the wastegate
actuator and connect the Mityvac hand pump in its
place .
3) Use the pump to apply pressure according to the
manufacturer’s specification .
4) Watch for the control rod to move and then hold
its position .
5) If the rod doesn’t move or hold its position, or if
the pressure leaks down as indicated by the gauge
on the hand pump, replace or repair the wastegate
actuator .
6) If no leak is found, disconnect the actuator rod
and move the wastegate flapper lever to determine
if it is stuck or seized .
7) If it does not move freely, the wastegate should
be replaced or repaired .
Idle Test
8) Start with the exhaust system cold .
9) Disconnect the pressure hose from the wastegate
actuator and connect the Mityvac hand pump in its
place .
10) Start the engine and allow it to idle .
11) After a short time, the exhaust inlet to the wa-
stegate should warm up, but the bypass line out of
the wastegate should remain cool .
1) If the bypass line heats up at this point, exhaust
is leaking past the wastegate, and the wastegate
should be replaced or repaired .
13) Use the pump to apply pressure to open the
wastegate according to the manufacturer’s specifica-
tion .
14) Feel the bypass line . It should begin to warm up
as the wastegate opens .
15) If not, the wastegate is stuck closed and should
be replaced or repaired .
16) Once testing is complete, bleed the pressure
from the pump and watch for the wastegate to
close .
Bench Testing
A Mityvac hand pump should be used to bench test-
ing the turbocharger wastegate, and adjusting the
control arm after replacement or repair . Follow the
manufacturer’s procedures for performing these
precision tests and adjustments .
turbocharGer wasteGate
FIGURE 7: TURBOCHARGER
Pressure
Connection
Wastegate Actuator