Tune-Up - 4.1l 6-cyl VIN [d] 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.

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 Federal emission vehicles are equipped with Delco-Remy High Energy Ignition (HEI). The California emission vehicles are equipped with the HEI-EST system.

Timing Mark and Firing Order Magnetic probe located at 10 Degrees ATDC. Scheme 18

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.
3. On Federal emission vehicles (HEI equipped), disconnect and plug vacuum hose at distributor. Set ignition timing at specified engine speed. Unplug and reconnect the vacuum hose.
4. On California emission vehicles (HEI-EST equipped), disconnect 4 wire connector at distributor and set ignition timing at specified engine speed. Reconnect 4 wire connector and clear ECM trouble code.

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 distribu- tor. 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.

1. Remove carburetor from engine. Invert throttle body and make two parallel cuts on each side of the locator point with a hacksaw. Cuts should not extend more than 1/8" (3.2 mm) beyond the locator point. (Scheme 19)
2. Place a flat punch near the end of the saw marks. Hold the punch at a 45° angle. Drive it into the throttle body until the casting breaks away, exposing the steel plug.
3. Hold a center punch in a vertical position and drive it into the plug. Now hold punch at a 45° angle, and drive plug out of casting.

Removing Idle Mixture Plug Distance between saw cuts depends on the size of the punch to be used. Scheme 19

IDLE MIXTURE ADJ. (PROPANE ENRICH) - FED. EMISSIONS

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. Engine must be at normal operating temperature and air conditioning off. Set parking brake and block drive wheels. On vehicles equipped with vacuum parking brake release, disconnect and plug hose at brake.
2. Disconnect and plug vacuum as directed on the Vehicle Emission Control Information label. Connect tachometer to engine. Adjust timing and reconnect vacuum advance hose. Set idle speed.
3. Disconnect crankcase ventilation tube from air cleaner. Using tool J-26911 (or equivalent), insert hose with rubber stopper (from propane valve) into air cleaner snorkel. Be sure propane cartridge is vertical.
4. With engine idling in "D" (Automatic) or "Neutral" (Manual), open propane supply control valve slowly. Engine speed will increase. Add propane until engine speed begins to drop from over-richness. Note maximum enriched idle RPM.
5. The maximum enriched idle RPM is the idle RPM plus propane enrichment RPM. Engine speed should rise above normal idle by amount specified. If so, mixture is correct. Proceed to step 9.
6. If speed is incorrect, remove idle mixture screw plugs. Carburetor must be removed and punch driven through bottom of throttle body to remove plug. Seat screws, then back out 3 turns.
7. Place transmission in "D" (Automatic) or "Neutral" (Manual), then back out screw slowly until maximum idle speed is reached. Then set maximum enriched idle speed.
8. Turn each mixture screw in (clockwise) 1/8 turn at a time until idle speed is correct. Recheck maximum enriched speed with propane. If incorrect, repeat step 7. Check and adjust fast idle speed.
9. Turn off engine. Remove propane tool, connect crankcase ventilation tube and reconnect all vacuum hoses.

PROPANE ENRICHED RPM

IDLE MIXTURE ADJUSTMENT - CALIFORNIA EMISSIONS

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. Remove carburetor from engine and remove idle mixture screw plug. Turn mixture screw in until lightly seated and back out 4 turns. If plug in air horn covering idle air bleed has been removed, replace air horn.
2. Remove vent stack screen assembly to gain access to lean mixture screw. Turn lean mixture screw until lightly bottomed and back out 2 1/2 turns. Some resistance should be felt. If no resistance, remove screw and check for spring.
3. Install carburetor on engine. DO NOT install air cleaner. Disconnect bowl vent line at carburetor. Disconnect the EGR valve hose and canister purge hose at carburetor and cap carburetor ports.
4. Disconnect carburetor-to-temperature sensor hose on air cleaner and plug open hose. Connect a dwell meter lead to the mixture control solenoid dwell test lead (green connector).
5. Set dwell meter to 6-cylinder position. Connect a tachometer to distributor lead (brown connector). Transmission should be in "PARK" or "NEUTRAL". Start engine and bring to operating temperature.
6. Run engine at 3000 RPM and adjust the lean mixture screw slowly to allow time for dwell to stabilize. It is normal for dwell to vary over a narrow range of approximately 5°.
7. Turn screw to obtain a average dwell of 35°. If unable to adjust, inspect main metering circuit for leaks or restrictions. Return engine to idle.
8. Adjust idle mixture screw to obtain average dwell of 25° with cooling fan in off cycle. Adjustment is very sensitive. Make final check with adjusting tool removed.
9. If unable to adjust, inspect idle system for leaks or restrictions. Disconnect mixture control solenoid when cooling fan is in off cycle and check for an RPM change of at least 50 RPM. If RPM does not change, check idle air bleed circuit.
10. Run engine at 3000 RPM for a few moments and note dwell reading. Dwell should show an average of 35°. If not, reset lean mixture screw. Then reset idle mixture screw to obtain 25° dwell.
11. When dwell readings have been set, reconnect all hoses and install vent screen and air cleaner. Set idle speed.

AUTOMATIC CHOKE

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

COLD (FAST) IDLE RPM

Place fast idle screw on high step of fast idle cam. Turn screw 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 SYSTEMS.

FAST IDLE SPEED (RPM)

HOT (SLOW) IDLE RPM

1. Make adjustments with engine at normal operating temperature, choke full open, air cleaner installed and air conditioning off. Disconnect solenoid wire and set base idle speed with idle speed screw.
2. Reconnect solenoid wire and all hoses. If vehicle is equipped with air conditioner, disconnect electrical lead from compressor and turn A/C switch ON. Open throttle slightly to allow solenoid to extend, then adjust curb idle by turning screw in back of solenoid.

SLOW IDLE SPEED

THROTTLE POSITION SENSOR (TPS) ADJUSTMENT

Note. This procedure only applies to the California Emission engine. The federal emission engine is not equipped with a TPS.

1. DO NOT remove the TPS adjustment screw plug unless the, TPS is not adjusted correctly or it is necessary to replace the air horn assembly, float bowl, TPS sensor, or TPS adjustment screw.
2. Using a .078" (1.98 mm) drill, carefully drill a hole in, the steel cup plug covering the TPS adjustment screw. Plug is located next to the TPS plunger bore. Remove steel plug using a small slide hammer.
3. Disconnect the TPS connector and jumper all three terminals. Connect a digital voltmeter from TPS connector center terminal (B) to bottom terminal (C).
4. With ignition on, engine stopped, turn the TPS screw with flat bladed screwdriver to obtain .26 volts at curb idle position. Air conditioner must be off and Idle Speed Control fully retracted.
5. After adjustment, a new cup plug or silicone sealant rubber RTV must be inserted in the air horn.

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