Page 34

1-30 GENERAL INFORMATION AND MAINTENANCE On models not equipped with positive stop shoulders, perform the sleps outlined in this procedure. 1. Remove the rocker covers and gaskets. 2. Crank the engine until the mark on the damper aligns with the TDC or 0 mark on the timing tab and the engine is in No. 1 firing position. Tils can be determined by placing your finger on the No. 1 cylinder valves as the marks align. If the valves do not move, it is in No. 1 firing position. If the valves move, it is in No. 6 firing position (No. 4 on the V6) and the crankshaft should be rotated 1 more revolution to the No. 1 firing positions To adjust a valve, back off the adjusting nut until lash (play) is felt at thti pushrod. Tighten the nut just until all lash is removed. This can be dietermined by rotating the pushrod with your fingers. When all lash is removed, the pushrod will stop rotating. When all play is removed, tighten the iuM

Idle Speed and Mixture Adjustments CARBURETED ENGINES Mixture screws are concealed under staked-in plugs. Idle mixture is adjustable only during carburetor overhaul, and requires the addition of propane as an artificial mixture enricher. For these reasons, mixture adjustments are not considered part of routine maintenance. Refer to Section 5 for these procedures. 4.8L Engines CURB IDLE SPEED

With the engine in No. 1 firing position, the following valves can adjusted: V6 Engines • Exhaust—1,5, • Intake—1,2, 3 V8 Engines • Exhaust—1,3,4,8 • Intake—1,2,5,7 Crank the engine 1 full revolution until the marks are again in ah nment. This is No. 6 firing position (No. 4 on the V6). The following valves cannow be adjusted: V6 Engines • Exhaust—2, 3, 4 • Intake—4,5, 6 V8 Engines • Exhaust—2,5,6,7 • Intake—3,4, 6. 5. Reinstall the rocker arm covers using new gaskets. 6. Install the distributor cap and wire assembly.

I See Figure 113 With the idle speed solenoid energized, turn the solenoid body to establish the curb idle speed shown on your underhood sticker. BASE IDLE SPEED With the solenoid wire disconnected, turn the V& in. hex head solenoid plunger adjusting screw to establish the base idle speed shown on your underhood sticker. 5.7L Engines I See Figures 114 and 115 1. All adjustments should be made with the engine at normal operating temperature, air cleaner on, choke open, and air conditioning off, unless otherwise noted. Set the parking brake and block the rear wheels. Automatic transmissions should be set in Drive, manuals in Neutral, unless otherwise noted in the procedures or on the emission control label.

1 PREPARE VEHICLE FOR ADJUSTMENTS - SEE EMISSION LABEL ON VEHICLE NOTE IGNITION TIMING SET_ PER LABEL

84903157

Fig. 112 Adjusting the valve—gasoline engines

3 SOLENOID ENERGIZED A / C COMPRESSOR LEAD DISCONNECTED AT A7C COMPRESSOR, A7C ON, A/T TRANSMISSION IN DRIVE

Fig. 1131 le speed adjustment—4.81 engines

I. PREPARE VEHICLE FOR ADJUSTMENTS - SEE EMISSION LABEL ON VEHICL NOTE IGNITION TIMING SET PER LABEL

5. TURN SCREW TO ADJUST TO SPECIFIED PRM. (RECONNECT A/C COMPRESSOR LEAD AFTER ADJUSTMENT) ELECTRICAL CONNECTION 4 OPEN THROTTLE SLIGHTLY TO ALLOW SOLENOID PLUNGER TO FULLY EXTEND

2 TURN IDLE SPEED SCRE TO SET CURB IDLE SPEED SPECIFICATIONS - AyC OF (SEE EMISSION LABEL)

Fig. 115 Idle speed adjustment—5.7L engines with solenoid

Fig. 114 Idle speed adjustment—5.7L engines without solenoid

2. Refer to the underhood emission sticker and prepare the vehicle for adjustment as specified on the sticker. On models without a solenoid, turn the idle speed screw to obtain the idle speed listed in the underhood emission control label. On models with a solenoid, turn the solenoid screw to obtain the idle speed listed in the underhood emission control label. Disconnect the wire at the air conditioning compressor and turn the ait conditioning on. Rev the engine momentarily to fully extend the solenoid plunger. Turn the solenoid screw to obtain the solenoid idle speed listed on the underhood emission sticker. Reconnect the air conditioning wire at the compressor. GASOLINE FUEL INJECTED ENGINES The fuel injected vehicles are controlled by a computer which supplies the correct amount of fuel during all engine operating conditions and controls idle speed; no adjustment is necessary or possible.

1990 gmc sierra service repair manual  
1990 gmc sierra service repair manual  
Advertisement