Tune-Up - 4.8l 6-cyl VIN [t] GMC Vandura I

ENGINE IDENTIFICATION

Engines can be identified by the eighth digit of the Vehicle Identification Number (VIN). The VIN number is stamped on a plate located on the upper left corner of the dash on all models except for "P" (Van conversion) models, which is located on the upper left corner.

VIN ENGINE CODES

TUNE-UP NOTES

Note. When performing tune-up procedures described in this article, the following notes and precautions must be observed

Due to changes and corrections, always refer to Engine Tune-Up Decal in engine compartment before attempting tune-up. In the event of a conflict between specifications given in this manual and decal specifications, decal specifications prevail.

When performing tune-up on vehicles equipped with a catalytic converter, do not allow or create a condition of engine misfire in one or more cylinders for an extended period of time. Damage to converter from overheating may occur due to loading with unburned fuel.

ENGINE COMPRESSION

When making compression checks, disconnect ignition switch Pink power feed wire from High Energy Ignition system. With air cleaner removed and throttle and choke wide open, crank engine through at least four compression strokes.

COMPRESSION SPECIFICATIONS

VALVE CLEARANCE

All engines have hydraulic lifters which should be adjusted to 1 turn down from zero lash.

VALVE ARRANGEMENT

E-I-I-E-E-I-I-E-E-I-I-E (Front to rear)

FIRING ORDER & DISTRIBUTOR/PICKUP INFORMATION

All vehicles are equipped with plain Delco-Remy High Energy Ignition (HEI).

Timing Mark and Firing Order Magnetic probe located at 10 Degrees ATDC. Scheme 20

DISTRIBUTOR PICKUP COIL RESISTANCE

IGNITION TIMING

Note. Engines are equipped with a receptacle for magnetic probe timing equipment, located 10° ATDC. DO NOT use this location for timing with a conventional light.

1. Install timing light with an adapter between No. 1 spark plug and No. 1 spark plug wire, or use an inductive type pickup. DO NOT puncture wire.
2. Ignition timing is set with the engine at normal operating temperature, choke full open, air cleaner installed and air conditioner off. Disconnect and plug vacuum hose at distributor. Set ignition timing at specified engine speed.

IGNITION TIMING

SPARK PLUG SPECIFICATIONS

SPARK PLUG SPECIFICATIONS

SPARK PLUG PART NUMBER

HIGH TENSION WIRE RESISTANCE

Carefully remove ends of wire from spark plug and distributor. Using an ohmmeter, check resistance while gently twisting wire. If resistance is incorrect, or fluctuates from infinity to any value, replace cable.

RESISTANCE

IGNITION COIL SPECIFICATIONS

COIL RESISTANCE

COIL OUTPUT

CARBURETOR USAGE

CARBURETOR USAGE

FUEL PUMP SPECIFICATIONS

To test pressure, pinch off fuel return line (if equipped) and connect pressure gauge to fuel line at carburetor. Hold pressure gauge at level of pump outlet.

FUEL PUMP

MIXTURE SCREW PLUG REMOVAL

Note. Mixture adjustment is not a normal tune-up procedure. DO NOT remove idle mixture plugs unless vehicle fails emissions testing or throttle body has been disassembled.

IDLE MIXTURE ADJUSTMENT (LEAN DROP)

Note. Mixture adjustment is not a normal tune-up procedure. DO NOT remove idle mixture plugs unless vehicle fails emissions testing or throttle body has been disassembled.

1. Set parking brake and block drive wheels. Remove air cleaner for access to carburetor, but keep vacuum hoses connected. Disconnect and plug other hoses if directed on Emission Control Tune-Up decal.
2. Warm engine to normal operating temperature. Make sure choke is open and air conditioning "OFF". Connect a tachometer to engine. Disconnect and plug distributor vacuum advance hose.
3. Check ignition timing and adjust if necessary. Reconnect vacuum advance hose. Carefully remove limiter cap from idle mixture. screw. Lightly seat mixture screw, then back out just enough so engine will run.
4. Place transmission in neutral. Back out mixture screw slowly until maximum idle speed is obtained. Reset curb idle speed to 775 RPM. Turn mixture screw in until idle speed is 700 RPM.
5. Reset curb idle speed to 775 RPM. Reconnect all hoses and install air cleaner, then recheck idle speed.

AUTOMATIC CHOKE

All choke caps are retained with rivets and are non-adjustable.

COLD (FAST) IDLE RPM

Place cam follower on high step of fast idle cam. Support lever with pliers and bend tang in or out to adjust fast idle RPM.

Note. On models with manual choke, rotate fast idle cam clockwise to farthest "UP" position.

Note. For choke information, see AUTOMATIC CHOKE under FUEL SYSTEM.

FAST IDLE SPEED (RPM)

HOT (SLOW) IDLE RPM

1. Make adjustments with engine at normal operating temperature, choke full open, air cleaner installed, air conditioning off and transmission in neutral. Disconnect solenoid wire and set base idle speed with hex head screw in rear of solenoid.
2. Reconnect solenoid wire. Set curb idle speed by turning solenoid assembly in or out. Ensure solenoid is energized and fully extended.

SLOW IDLE SPEED

EMISSION CONTROL

No emission control information in this contained in this article. Please see the appropriate article in the EMISSIONS section.

ALTERNATOR

All models are equipped with Delco-Remy Integral Regulator Alternators.

ALTERNATOR SPECIFICATIONS

ALTERNATOR REGULATOR

All models are equipped with Delco-Remy non-adjustable regulator, integral with alternator.

REGULATOR SPECIFICATIONS

BATTERY

BATTERY SPECIFICATIONS

STARTER

All starters are Delco-Remy overrunning clutch models.

STARTER SPECIFICATIONS

BELT TENSION ADJUSTMENTS

BELT ADJUSTMENT

BASIC SERVICE INTERVALS

REPLACEMENT INTERVALS

FLUID CAPACITIES

FLUID CAPACITIES

See also:
• AUTOMATIC CHOKE