Housing Pressure Cold Advance; Injection Line Replacement - GMC G Service Manual

A. Vacuum Gage
B. Pigtail Connector
C. Clockwise Rotation
HOUSING PRESSURE COLD
ADVANCE
The Housing Pressure Cold Advance feature advances
the injection timing about four degrees during cold opera­
tion. This provides better cold starts, and improved cold idle
and emission control.
With the LL4 Heavy-Duty Emissions engine, the circuit is
actuated by a coolant temperature switch on the rear of the
right cylinder head. The switch is calibrated to open the
circuit at 35 degrees C (95 degrees F). Below the switching
point, timing is advanced by decreasing housing pressure
from 68.95 kPa (10 psi) to zero. Above the switching point,
the housing pressure is returned to 68.95 kPa (10 psi). The
fast idle solenoid is energized by the same switch.
The LH6 engine system is explained in DIESEL EMIS­
SIONS (SEC. 6E2).
DIESEL FUEL INJECTION 6C2-3
D. To Vacuum Source
E. Wide Open Stop Pin
F. J 36142
Figure 2 — VR V /D etent Switch A djustm ent
M
M
10. Injection lines at the pump.

INJECTION LINE REPLACEMENT

Clean
• All line fittings that will be loosened or removed.
Remove or Disconnect (Figures 4 and 5)
1. Negative battery cables.
2. Engine cover (G-Models only).
3. Air cleaner at the valve cover.
4. Crankcase ventilator bracket.
5. Intake manifold bolts.
• It may be necessary to loosen the vacuum
pump hold-down clamp and rotate the pump to
gain access to all intake manifold bolts.
6. Injection line clips.
7. Intake manifold. Refer to 6.2 LITER DIESEL (SEC.
6A6).
8. Injection line clips at the loom brackets.
• Raise the vehicle (left bank of G-Models only).
9. Injection lines at the nozzles.
• Cap the lines and nozzles immediately.
• Do not bend injection lines.
• Cap the lines and the pump fittings immediately.
• Tag the lines for installation.
L00722