Tune-Up - v6 GMC Pickup 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 visible through windshield.

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

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

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, replace wire.

HIGH TENSION WIRE RESISTANCE (OHMS)

DISTRIBUTOR

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

2.8L Firing Order & Timing Marks. Scheme 12

4.3L Firing Order & Timing Marks. Scheme 13

2.8L & 4.3L

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. Disconnect 1-wire (Tan with Black stripe) connector. On 4.3L engines, this connector is located near 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 Drive (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. Verify correct controlled idle speed. Perform idle air control check before adjusting hot idle. Refer to appropriate article in COMPUTERIZED ENGINE CONTROLS section.

1. Remove air cleaner and gasket. With Idle Air Control IAC) valve connected, ground terminal "A" to "B" at ALDL connector. (Scheme 14)
2. Turn ignition switch on, 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. Install a tachometer and start engine. Allow engine to reach operating temperature. Adjust idle screw to specification with vehicle in Neutral. Turn ignition switch off. Reconnect IAC valve electrical connector. Install air cleaner and gasket.
5. This procedure will set a code 35. Erase code by disconnecting electrical power to ECM for 30 seconds. Electrical power is disconnected when negative battery cable or ECM fuse is removed. Ignition must be in "OFF" position to prevent damage to ECM.

SLOW IDLE SPEED (RPM)

Scheme 14

ADJUSTMENTS

Note. Throttle Position Sensor (TPS) is not adjustable on 4.3L. Adjustment should only be performed when throttle body parts have been replaced or after slow 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.

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

Idle mixture is not adjustable on TBI models.

COLD (FAST) IDLE RPM

Fast idle is not adjustable on TBI engines.

FUEL PUMP

All models are equipped with an in-tank, electric fuel pump.

FUEL PUMP SPECIFICATIONS

EMISSION CONTROL SYSTEMS

See EMISSIONS section.

DISTRIBUTOR PICK-UP COIL RESISTANCE

IGNITION COIL

1. Disconnect all electrical connections from ignition coil. Connect an ohmmeter at connection "A". (Scheme 15) Reading should be infinite. If reading is not infinite, replace the coil.
2. Connect an ohmmeter at connection "B". (Scheme 15) 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 15) Using high scale, meter should show continuity. If reading is infinite, replace coil. Connect all coil connections and ensure coil ground is clean.

Scheme 15

FUEL SYSTEMS

Engine uses General Motors Model 220 Throttle Body Injection (TBI).

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

The 2.8L and 4.3L V6 engines use a single "serpentine" accessory drive belt. Correct tension is automatically maintained. No adjustment is necessary.

SERVICE INTERVALS

REPLACEMENT INTERVALS

CAPACITIES

FLUID CAPACITIES

SYSTEM REFRIGERANT CAPACITIES