Tune-Up - v6 GMC Cab & Chassis R2500

ENGINE IDENTIFICATION

Engines can be identified by the eighth character of the Vehicle Identification Number (VIN). The VIN number is stamped on a plate attached to the top left side of dash.

ENGINE CODES

TUNE-UP NOTES

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

Always refer to Emission Control Label in engine compartment before attempting tune-up. If manual and label differ, always use emission label specifications.

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 connector Pink wire from high energy ignition system. Remove air cleaner. Open throttle and choke fully. Remove all spark plugs. Crank engine through at least 4 compression strokes.

COMPRESSION SPECIFICATIONS

SPARK PLUGS

SPARK PLUG TYPE

SPARK PLUG SPECIFICATIONS

HIGH TENSION WIRE RESISTANCE

Carefully remove ends of wire from spark plug and distributor. Twist spark plug boot 1/2 turn before removing. Using an ohmmeter, check resistance while gently twisting wire. If resistance is not within specification, or fluctuates from infinity to any value, replace wire.

HIGH TENSION WIRE RESISTANCE (OHMS)

2.8L

1. E-I-I-E-I-E (Left bank, front-to-rear).
2. E-I-E-I-I-E (Right bank, front-to-rear).

4.3L

1. E-I-E-I-I-E (Left bank, front-to-rear).
2. E-I-I-E-I-E (Right bank, front-to-rear).

VALVE CLEARANCE

All engines use hydraulic lifters.

VALVE CLEARANCE ADJUSTMENT

DISTRIBUTOR

All models are equipped with Delco HEI-Electronic Spark Timing (HEI-EST) distributors.

2.8L Firing Order & Timing Marks. Scheme 7

4.3L Firing Order & Timing Marks. Scheme 8

IGNITION TIMING

1. Install timing light with an adapter between No. 1 spark plug and No. 1 spark plug wire or use an inductive pick-up. Do not puncture wire. On 4.3L engines, disconnect 1-wire (Tan with Black stripe) connector at distributor. On 2.8L engines, this wire connector is located in a taped section below heater case in passenger compartment. NOTE: Some GM engines use a magnetic timing probe hole for use with special electronic timing equipment. See equipment manufacture's directions for use of this equipment
2. Check and adjust ignition timing with engine at normal operating temperature and transmission in "P" or "N" (auto. trans.) or Neutral (man. trans.) Reconnect 1-wire connector. Clear trouble code by removing ECM power fuse for 10 seconds.

IGNITION TIMING SPECIFICATIONS (DEGREES BTDC @ RPM)

HOT (SLOW) IDLE RPM

Note. Adjustment is necessary only when throttle body assembly has been replaced.

1. Remove air cleaner and gasket. Plug TBI unit vacuum port for THERMAC (Thermostatic Air Cleaner). With Idle Air Control (IAC) valve connected, ground terminal "A" to "B" at ALDL connector.
2. Turn ignition switch to "ON" position, DO NOT start engine. Wait approximately 30 seconds for IAC valve pintle to extend and seat in throttle body.
3. With ignition on, disconnect IAC valve electrical connector. Remove ground at ALDL connector. Using an awl, remove plug for minimum idle speed adjustment by piercing, then applying leverage.
4. Start engine. Adjust idle screw to specification. Turn ignition switch "OFF". Reconnect IAC valve electrical connector. Install air cleaner and gasket.

SLOW IDLE SPEED (RPM)

THROTTLE POSITION (TPS) ADJUSTMENT

Note. Adjustment should only be performed when throttle body parts have been replaced or after minimum idle speed has been adjusted.

Connect digital voltmeter between TPS connector terminals "A" and "B" using jumper wires. With ignition on and engine stopped, TPS voltage should be between .42 and .54 volts. Rotate TPS to obtain correct voltage reading. If voltage cannot be adjusted to proper specification, replace TPS.

TPS OUTPUT VOLTAGE CHECK

Note. On 4.3L models, Throttle Position Sensor (TPS) is not adjustable.

Connect digital voltmeter between TPS connector terminals "A" and "B" using jumper wires. With ignition on and engine stopped, TPS voltage should be less than one volt. Replace TPS if voltage is more than one volt. Before replacing TPS, ensure minimum idle speed is set correctly.

IDLE MIXTURE

Note. Idle mixture not adjustable on TBI models.

COLD (FAST) IDLE RPM

Note. No fast idle adjustments are possible on TBI engines.

IGNITION

DISTRIBUTOR PICK-UP COIL RESISTANCE

IGNITION COIL

1. Disconnect all electrical connections from coil. Connect an ohmmeter at connection A. (Scheme 9) Reading should be infinite. If reading is not infinite, replace coil.
2. Connect an ohmmeter at connection B. (Scheme 9) Using low scale, reading should be very low or zero. If reading is not low or zero, replace coil.
3. Connect an ohmmeter at connection C. (Scheme 9) Using high scale, meter should show continuity. If reading is infinite, replace coil. Connect all coil connections and ensure coil ground is clean.

Scheme 9

EMISSION CONTROL

See EMISSIONS section.

FUEL SYSTEMS

All models are equipped with Throttle Body Injection (TBI), using General Motors Model 220 throttle body.

FUEL PUMP

Fuel pump is electronic and is located in fuel tank. Inspect attaching hose and insulation at bottom of pump for deterioration.

FUEL PUMP SPECIFICATIONS

BATTERY

BATTERY SPECIFICATIONS @ 0°F (-18°C)

STARTER

All engines are equipped with Delco overrunning clutch starters.

STARTER SPECIFICATIONS

ALTERNATOR

All engines are equipped with Delco alternators with integral voltage regulator.

ALTERNATOR SPECIFICATIONS @ 80°F (27°C)

ALTERNATOR REGULATOR

All engines are equipped with Delco nonadjustable voltage regulators, integral with alternator.

BELT ADJUSTMENT

Using a strand tension gauge, measure belt tension midway between pulleys. If tension is not as specified, adjust tension or replace belt.

BELT ADJUSTMENT TENSION IN LBS. (KG) USING STRAND TENSION GAUGE

SERVICE INTERVALS

REPLACEMENT INTERVALS

CAPACITIES

FLUID CAPACITIES

SYSTEM REFRIGERANT CAPACITIES