Page 28
DESCRIPTION AND OPERATION
The VTG Position Control Valve, which is located
on the intake manifold at the No. 4 cylinder
position, provides the modulated air pressure
required for opening and closing the turbine
vanes. The control valve is an electrically
controlled pneumatic assembly (Figure 18) that
either increases, decreases or maintains air
pressure based on commands sent by the EECU.
An air valve having this capability must constantly
bleed air pressure. This bleed air is released
directly to the atmosphere from a 1-inch diameter
port on the lower front side of the valve assembly.
18
Figure 18 — VTG Position Control Valve
On early-production engines (prior to May 4,
2004), supply air enters the control valve directly
from the chassis air system. As a result, small
amounts of oil mist in the chassis air system can
condense inside the valve. It is a normal condition
to notice some oil seepage from the bleed port.
Engines produced after May 4, 2004 have an oil
coalescing air filter (Figure 19) incorporated into
the air line supplying the control valve to prevent
oil condensation and possible “coking” inside the
VTG position control valve. The filter is mounted
on a bracket at the lower side of the cylinder
block, to the rear of the oil filters. A service parts
kit is available to retrofit early-production engines
if conditions warrant it.
19
Figure 19 — Coalescing Air Filter
1. Outlet Port 2. Inlet Port
5-111.bk Page 28 Monday, July 10, 2006 2:26 PM
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