On-Vehicle Service - GMC G Service Manual

6C2-2 DIESEL FUEL INJECTION
IDLE SPEED ADJUSTMENT
CURB IDLE SPEED (Figure 1)
Tool Required:
J 26925 Tachometer
1. Set the parking brake and block the drive wheels.
2. Engine must be at normal operating temperature with
the air cleaner on and all accessories turned off.
3. Install J 26925 or equivalent per manufacturer's
instructions.
4. Adjust the low idle speed screw (2) on the fuel injec­
tion pump to obtain the curb idle speed shown on the
Emission Control Information label.
FAST IDLE SPEED (Figure 1)
Tool Required:
J 26925 Tachometer
1. Set the parking brake and block the drive wheels.
2. Engine must be at normal operating temperature with
the air cleaner on and all accessories turned off.
3. Install J 26925 or equivalent per manufacturer's
instructions.
4. Remove the connector from the fast idle solenoid.
5. Connect an insulated jumper wire from the positive
battery terminal to the solenoid terminal. This will
energize the solenoid.
6. Open the throttle momentarily to energize and fully
extend the fast idle solenoid plunger.
7. Adjust the extended fast idle solenoid plunger (3) by
turning the hex head to obtain the fast idle speed
shown on the Emission Control Information label.
8. Remove the jumper wire and install the connector to
the fast idle solenoid.

ON-VEHICLE SERVICE

VACUUM REGULATOR VALVE
ADJUSTMENT (LL4 ENGINE WITH
AUTOMATIC TRANSMISSION)
Tools Required:
J 33043-A Gage Block
J 36142 Switch Gage Tool
1. Loosen the vacuum regulator valve (VRV) so it is free
to rotate on the pump.
2. Attach a vacuum source of 67 ± 5 kPa (20 inches Hg
± 1.5 inch Hg) to the bottom vacuum port of the VRV.
3. Attach a vacuum gage to the top vacuum port (figure
2 ).
4. Insert a .646-inch gage block (J 33043-A) between
the gage boss on the injection pump and the wide-
open stop screw on the throttle lever (switch on posi­
tion) (figure 3).
5. Rotate the throttle shaft and hold it against the gage
block.
NOTICE: Valve must be set while rotating the
valve body clockwise only.
6. Slowly rotate the vacuum regulator valve body clock­
wise (facing the valve) until the vacuum gage reads
38.8 ± 2 kPa (11.5 ± 0.6 inches Hg). Hold the valve
body at this position and tighten the mounting screws
to 6 N»m (54 in. lbs.).
7. Check by allowing the throttle shaft to return to the
idle stop position, then rotate the throttle shaft back
against the gage block and read the vacuum gage.
The gage should read 38.8 ± 2 kPa (11.5 ± 0.6
inches Hg). If vacuum is outside of limits, reset the
valve.
8. With the vacuum regulator valve vacuum set, confirm
the detent switch point by reading the resistance
between the ignition terminal (pink with black stripe)
and the detent terminal (orange).
9. Insert J 36142 between the wide-open stop pin and
the wide-open stop screw on the throttle lever.
10. Rotate the throttle lever against the tool. There should
be no continuity (infinite resistance).
11. Release the throttle lever and remove the switch
gage tool.
12. Rotate the throttle lever to wide-open throttle (the
lever stop screw touching the pump stop pin).
13. Check the switch for continuity. The switch must have
continuity (1 to 0 ohms) before the throttle reaches
the wide-open throttle position. If the switch does not
meet these specifications, reset the assembly by
returning to step 1 and repeating the entire
procedure.