Tune-Up - v8 GMC Value Van P2500

ENGINE IDENTIFICATION

Engines can be identified by the eighth character of the Vehicle Identification Number (VIN). The VIN number is stamped on a plate located at the base of the steering column on "P" models, and on a plate at the upper left corner of the dash on all other models.

Engine code numbers are located at front of block, at right cylinder head on 5.0L and 5.7L engines and in front of intake manifold on 7.4L engines.

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 Emission Control Label in engine compartment before attempting tune-up. In the event of a conflict between specifications given in this manual and label specifications, label specifications prevail.

For tune-up purposes, "Light Duty" refers to vehicles up to 8500 lbs. "Heavy Duty" refers to vehicles exceeding 8500 lbs.

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. With throttle and choke wide open, and all spark plugs removed, 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. Using an ohmmeter, check resistance while gently twisting wire. If resistance is not to specifications, or fluctuates from infinity to any value, replace cable.

HIGH TENSION WIRE RESISTANCE

5.0L & 5.7L

E-I-I-E-E-I-I-E (Both banks, front-to-rear).

7.4L

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

VALVE CLEARANCE

All vehicles are equipped with hydraulic lifters. Lifters should be adjusted to zero lash.

DISTRIBUTOR

California 5.0L and 5.7L engines are equipped Delco-Remy High Energy Ignition with Electronic Spark Timing (HEI-EST).

Federal 5.0L high compression (9.2:1) engines use Electronic Spark Control (ESC) ignition system with detonation sensor.

All other engines are equipped with High Energy Ignition (HEI) systems and no adjustments are required.

Firing Order & Timing Mark (Magnetic Timing Pick-Up Is Located At 10 Degrees ATDC). Scheme 1

IGNITION TIMING

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

1. Connect an adapter between No. 1 spark plug wire or use an inductive pick-up. Do not puncture wires. Connect timing light according to manufacturer's instructions.
2. Check or adjust ignition timing with engine at normal operating temperature, and distributor vacuum line (if equipped) disconnected and plugged. Light duty models with automatic transmission should be checked in Drive; all others in Park or Neutral.
3. On California Models with HEI-EST and HEI-ESC distributors, disconnect 4-wire plug connector at distributor when checking ignition timing. Once timing has been set, reconnect connector and clear trouble code from computer.

IGNITION TIMING SPECIFICATIONS (DEGREES BTDC @ RPM)

HOT (SLOW) IDLE RPM

Note. Depending on engine size and application, either a vacuum operated throttle kicker assembly or an idle speed solenoid is used to control idle under load situations and to reduce emissions

Throttle Kicker

1. With engine at operating temperature, choke wide open and ignition timing set, adjust idle speed screw to obtain specified curb idle speed. See Emission Control Label.
2. Apply 20 in. Hg vacuum using vacuum pump to fully extend throttle kicker plunger. Manually open throttle slightly and then release. With plunger held inward, turn plunger in or out to obtain specified RPM. See Emission Control Label.

Idle Speed Solenoid

1. With engine at operating temperature, choke wide open and ignition timing set, adjust curb idle speed to specification by turning idle speed screw. See Emission Control Label.
2. With A/C off, disconnect A/C compressor lead at compressor. Turn A/C on with automatic transmission in "D" and manual transmission in neutral. This will energize solenoid.
3. Open throttle slightly to allow solenoid plunger to fully extend. Turn solenoid screw to set curb idle speed to specification on Emission Control Label. (Scheme 2)

Idle Speed Solenoid Adjustment. Scheme 2

Without Idle Speed Solenoid

With engine at operating temperature, set ignition timing to specification. Remove air cleaner and plug disconnected hoses. Turn idle speed screw to set curb idle to specification found on Emission Control Label.

IDLE SPEED (RPM)

Mixture Screw Plug Removal

1. Remove carburetor from engine and drain fuel. Invert carburetor. Make 2 parallel cuts in throttle body, one cut on each side of locator points beneath idle mixture needle plug.
2. The cuts should reach down to steel plug, but should not extend more than 1/8" beyond locator points. Distance between saw marks depends on size of punch to be used.
3. Place a flat punch at a point near ends of saw marks in throttle body. Holding punch at a 45° angle, drive it into throttle body until casting breaks away, exposing steel plug. Holding a center punch vertically, drive it into steel plug. Holding punch at a 45° angle, drive out steel plug.

Propane Enrichment Procedure (Federal Light Duty Models Only)

1. With engine at normal operating temperature, choke fully open and A/C off (if equipped), set parking brake and block drive wheels. Connect tachometer to engine. Disconnect vacuum advance and set timing to specification.
2. Reconnect vacuum advance. Set carburetor to idle speed. Disconnect crankcase ventilation tube from air cleaner. Insert hose with rubber stopper from propane valve into PCV tube opening in air cleaner. Propane bottle must be in vertical position.
3. Slowly open control valve until maximum engine speed is reached with transmission in "D" (auto. trans.) or Neutral (man. trans.). Observe propane flow meter to ensure propane cartridge is full. With propane flowing, observe idle speed. Continue to add propane until speed drops off.
4. Note maximum idle speed. If idle speed is within specification, mixture is correct. No further adjustments are necessary. If not correct, proceed with adjustment procedure.
5. Lightly seat idle mixture adjustment screws. Back out equally, just enough so engine will run. Place transmission in "D" (auto. trans.) or Neutral (man. trans.).
6. Turn each mixture screw out 1/8 turn at a time until maximum idle speed is reached. Set idle speed to enriched idle speed specification. Turn each idle mixture screw in 1/8 turn at a time until idle speed is at specification. See IDLE SPEED (RPM) table.
7. Recheck enrichment speed with propane. After adjustments are complete, seal idle mixture adjustment screws with RTV sealant. Turn off propane, unplug and reconnect all vacuum hoses. Install air cleaner. Recheck idle speed and repeat procedure if necessary.

PROPANE MIXTURE ADJUSTMENT (RPM)

Heavy Duty Models Only

1. Set parking brake and block drive wheels. Warm engine to normal operating temperature. Remove air cleaner. Place transmission in Neutral or Park and connect tachometer.
2. Turn idle mixture screws in lightly to seat them, then back out 2 turns. Do not turn screws tightly against seat or damage may result. With engine running, choke open, and transmission in Neutral, adjust idle speed to specification. Adjust mixture screws to obtain maximum RPM.
3. Readjust idle speed screw to specification, and readjust mixture screws to obtain highest RPM. Turn ignition off, and install air cleaner. Seal idle mixture screw with RTV sealant.

E4ME & E4MED MIXTURE ADJUSTMENT

Note. Idle mixture control plunger travel should be checked before mixture adjustment or disassembly.

Mixture Control Solenoid Plunger Travel

1. Hold plunger down against solenoid stop. Use Driver (J-28696-10 or BT-7928) to adjust lean stop screw, until solenoid plunger just contacts Gauging Rod (J-33815-1) when placed over throttle side metering jet rod guide.
2. Adjustment is correct when solenoid plunger contacts solenoid stop and gauging rod at same time. (Scheme 3)

Mixture Control Plunger Adjustment. Scheme 3

Note. Mixture must not be adjusted unless carburetor has been disassembled for cleaning or parts replacement or a systems performance check indicates that carburetor is cause of malfunction.

Idle Air Bleed Valve Adjustment

1. Install air bleed valve Gauging Rod (J-33815-2 or BT-8253-B) in throttle side "D" shaped vent hole in air horn casting. (Scheme 4) Upper end of gauge should be positioned over open cavity next to idle air bleed valve.
2. While holding gauging rod down lightly, so that solenoid plunger is against solenoid stop, adjust idle air bleed valve so that gauging rod will pivot over and just contact top of valve. No further adjustment is required.
3. Disconnect and plug canister purge hose at canister. Connect dwell meter. Place spacer.10-.75" (3-19 mm) between accelerator pump lever and TPS plunger. Start engine and allow it to reach operating temperature. Check idle dwell. If not within 25-35°, idle plugs will have to be removed and mixture screws adjusted.

Positioning Idle Air Bleed Valve (Hold Gauge Down Lightly). Scheme 4

Adjusting Idle Mixture Screws

1. Turn each mixture screw clockwise until lightly seated. Back out mixture screws 3 turns. Warm engine to operating temperature. While idling in "D" (auto. trans.) or Neutral (man. trans.) adjust both mixture screws equally in 1/8 turn increments until dwell reading varies within 25-35° range, attempting to be as close to 30° as possible.
2. If reading is too low, turn mixture screws counterclockwise. If reading is too high, turn screws clockwise. Allow time for readings to stabilize after each adjustment. When adjustments are completed, seal each screw with rubber sealer.

COLD (FAST) IDLE RPM

1. Place transmission in "P" (auto. trans.) or Neutral (man. trans.). Place cam follower on step of fast idle cam according to emission control decal. On light duty vehicles, disconnect and plug vacuum hose to EGR valve, canister purge hose and purge signal hose at canister.
2. Start engine without touching throttle. Turn fast idle speed screw to adjust speed to specification.

FAST IDLE SPEED (RPM)

THROTTLE POSITION SENSOR (TPS) E4ME & E4MED

Note. Adjust TPS only if it is not adjusted correctly, or if it is necessary to replace air horn assembly, float bowl, TPS sensor or TPS adjustment screw.

Scheme 5

1. Using a 5/64" drill bit, drill a 1/16" to 1/8" deep hole in aluminum plug covering TPS adjustment screw. Use care not to damage screw head. (Scheme 5) (Scheme 5): TPS Adjustment Screw Location For E4ME (Plug Must Be Drilled Out To Adjust Screw)
2. Start a No. 8, 1/2" long self-tapping screw in drilled hole, turning screw in only far enough to ensure good thread engagement. Using a screwdriver between screw head and air horn, pry out plug.
3. Using TPS Adjuster (J-28696), remove TPS adjusting screw. Connect digital voltmeter from TPS connector center terminal "B" to bottom terminal "C". With ignition on, and engine stopped, install and adjust TPS adjustment screw to obtain specified TPS voltage with A/C off.
4. Install new plug in air horn. If new plug is not available, use Delco Threadlock Adhesive (X-10) on TPS adjustment screw. Adjust voltage, as in step 3).

TPS VOLTAGE ADJUSTMENT

AUTOMATIC CHOKE

The choke cover on all engines is riveted in place. No adjustments are possible or necessary.

FUEL PUMP

FUEL PUMP SPECIFICATIONS

California 5.0L and 5.7L engines are equipped with Delco-Remy High Energy Ignition with Electronic Spark Timing (HEI-EST).

Federal 5.0L high compression (9.2:1) engines use Electronic Spark Control (ESC) ignition system with detonation sensor.

All other models are equipped with High Energy Ignition (HEI) systems and no adjustments are required.

Note. High energy ignition system module must be replaced as a unit. A liberal coat of silicone grease MUST be applied to both module and its mounting surface.

DISTRIBUTOR PICK-UP COIL RESISTANCE

IGNITION COIL

IGNITION COIL RESISTANCE - OHMS @ 75°F (24°C)

EMISSION CONTROL

For information on emission control systems, see EMISSION section.

FUEL SYSTEMS

CARBURETOR

ELECTRICAL

BATTERY SPECIFICATIONS @ 0°F (-18°C)

STARTER

All models are equipped with Delco-Remy overrunning clutch starters.

STARTER SPECIFICATIONS

ALTERNATOR

All models are equipped with Delco-Remy alternators with integral voltage regulators. No adjustments are possible.

ALTERNATOR SPECIFICATIONS @ 80°F (27°C)

ALTERNATOR REGULATOR

Regulators are Delco nonadjustable, integral with alternator.

REGULATOR SPECIFICATIONS

SERVICE INTERVALS

REPLACEMENT INTERVALS

BELT ADJUSTMENT

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

CAPACITIES

FLUID CAPACITIES

SYSTEM REFRIGERANT CAPACITY