Tune-Up - 4-cyl Chevrolet Cab & Chassis C20

ENGINE IDENTIFICATION

The 8th character of the Vehicle Identification Number (VIN) identifies the engine. The VIN number is stamped on a plate attached to the left top side of dash.

VIN ENGINE CODES

TUNE-UP NOTES

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

Due to changes and corrections, always refer to Engine Tune-Up Decal in engine compartment before attempting tune-up. If manual and decal specifications differ, use decal specifications.

When performing tune-up on vehicles equipped with a catalytic converter, do not allow or create an 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 (HEI) system. With air cleaner removed, throttle and choke wide open, 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 cap. Using an ohmmeter, check resistance while gently twisting wire. If resistance is not within specifications or fluctuates from infinity to any value, replace cable.

1.9L

1. Left Side - All intake.
2. Right Side - All exhaust.

2.5L

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

VALVE CLEARANCE

Check rocker arm bracket nuts for looseness and retighten as necessary before adjusting valves. Adjust valves with engine cold.

VALVE ADJUSTMENT

IGNITION COIL WIRE

Remove ignition coil wire from coil and distributor cap. Check terminals for corrosion and clean if necessary. Check coil wire resistance. Replace wire if resistance is excessive.

HIGH TENSION WIRE RESISTANCE

DISTRIBUTOR

All 1.9L engines are equipped with a Nippondenso electronic ignition distributor. Some 2.5L engines use Delco-Remy High Energy Ignition (HEI) distributor and some use Delco-Remy HEI with Electronic Spark Timing (EST). No adjustments other than timing are necessary.

1.9L 4-Cylinder Firing Order. Scheme 1

2.5L 4-Cylinder Firing Order. Scheme 2

IGNITION TIMING

1. Install timing light with adapter between No. 1 spark plug and No. 1 spark plug wire, or use inductive type pick-up. Do not puncture wire.
2. Run engine until it reaches normal operating temperature. Disconnect and plug distributor advance, EGR and canister purge vacuum hoses. Place transmission in Neutral (man. trans.) or Drive (auto. trans.). Check ignition timing and adjust if necessary. Reconnect all hoses.

IGNITION TIMING SPECIFICATIONS (DEGREES BTDC @ RPM)

1. Warm engine to normal operating temperature and place transmission in Neutral. California models must be in closed loop operation before checking or adjusting. Disconnect and plug distributor vacuum hose, canister purge line and EGR vacuum line.
2. Pinch off idle compensator vacuum hose by bending rubber hose. Adjust throttle adjusting screw to obtain specified idle RPM. If vehicle is equipped with A/C, turn A/C on maximum cold and high blower.
3. Open throttle momentarily to assure solenoid is fully extended, then let it close. Adjust screw on throttle lever to obtain solenoid RPM. Reconnect wires and hoses.

IDLE SPEED (RPM)

1. Remove air cleaner and gasket. Plug TBI unit vacuum port for THERMAC (Thermostatic Air Cleaner). Remove T.V. cable from throttle control bracket. Connect tachometer to engine.
2. Disconnect Idle Air Control (IAC) connector. Start engine and warm to normal operating temperature with transmission in Park (auto. trans.) or Neutral (man. trans.).
3. Install Air Passage Plug (J-33047) into throttle body idle air passage, ensure plug seats air tight. (Scheme 3)
4. If plug covers throttle stop screw hole, remove plug by drilling 5/32" hole through casting into plug. Using 1/16" punch, remove plug.
5. Using Torx Bit No. 20, turn throttle stop screw to adjust slow idle to specifications. Turn off engine and remove plug tool from throttle body air passage.
6. Install T.V. cable into throttle control bracket. Install IAC connector. Seal throttle stop screw with silicone sealant. Install air cleaner and gasket.

Installing Throttle Body Air Passage Plug. Scheme 3

IDLE SPEED (RPM)

IDLE MIXTURE

Note. On 2.5L, idle mixture is controlled by Electronic Control Module (ECM) and is nonadjustable. On 1.9L, do not adjust mixture unless carburetor has been disassembled or vehicle fails emissions testing.

Mixture Screw Plug Removal (1.9L)

Remove carburetor from vehicle. Drill hole into idle mixture screw plug. Insert screw into plug and pull plug out.

Mixture Adjustment (1.9L) Federal Models

1. Remove carburetor. Remove idle mixture screw plug. Reinstall carburetor. Block drive wheels and place transmission in Neutral.
2. Disconnect and plug distributor vacuum hose, idle compensator and EGR vacuum hoses. With engine at normal operating temperature, turn idle mixture screw all the way in, then back it out 1 1/2 turns. Adjust throttle screw to 850 RPM.
3. Adjust idle mixture screw to obtain maximum speed. Reset throttle screw to 850 RPM. Turn idle mixture screw clockwise to obtain 800 RPM.
4. If vehicle is equipped with A/C, turn on A/C to maximum cold and high blower. Open throttle about 1/3 and let it close. Adjust idle-up controller screw so engine speed is 900 RPM.

Mixture Adjustment (1.9L) California Models

1. Remove carburetor. Remove idle mixture screw plug. Reinstall carburetor. Make idle speed and mixture adjustment with engine at normal operating temperature.
2. Disconnect and plug distributor vacuum hose, canister purge hose and EGR vacuum hose. Block idle compensator hose by bending hose. Connect dwell meter (set to 4-cylinder scale) to dwell meter lead on carburetor.
3. Turn idle mixture screw all the way in, then back it out 1 1/2 turns. Set throttle adjusting screw to 850-950 RPM. Adjust idle mixture screw to obtain an average dwell of 36°. Reset throttle adjusting screw to 850-950 RPM.
4. If vehicle is equipped with A/C, turn on A/C to maximum cold and set blower on high. Open throttle 1/3 and let it close. Adjust idle-up controller screw to set idle at 900 RPM.

COLD (FAST) IDLE RPM

Note. On 2.5L engines, fast idle is controlled by Electronic Control Module (ECM) and is nonadjustable.

1. Run engine until warm. Disconnect and plug distributor, idle compensator and EGR vacuum hoses. Fast idle speed should be about 3200 RPM.
2. Throttle valve opening at first step of fast idle cam should be 15-17°. Adjust if necessary by turning fast idle screw.

COLD (FAST) IDLE (RPM)

AUTOMATIC CHOKE (1.9L)

Automatic choke is nonadjustable.

FUEL PUMPS

All 1.9L engines use a diaphragm type, mechanical fuel pump. All 2.5L engines are equipped with an in-tank, electric fuel pump.

FUEL PUMP SPECIFICATIONS

All 1.9L engines are equipped with a Nippondenso solid state distributor. All 2.5L engines are equipped with a Delco-Remy HEI solid state distributor. No adjustments are necessary.

DISTRIBUTOR PICK-UP COIL RESISTANCE

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

BELT ADJUSTMENT

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

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

ALTERNATOR REGULATOR

All models are equipped with Delco-Remy nonadjustable voltage regulator, integral with alternator.

REGULATOR OPERATING VOLTAGE

FUEL SYSTEMS

All 1.9L engines use Hitachi model DCH340 carburetor. All 2.5L engines use General Motors Model 300 Throttle Body Injection (TBI).

BATTERY

BATTERY SPECIFICATIONS

STARTER

All 1.9L and 2.5L engines use a Delco-Remy 5MT solenoid-actuated starter with overrunning clutch.

STARTER SPECIFICATIONS

ALTERNATOR

All models use a Delco-Remy alternator with integral voltage regulator.

ALTERNATOR SPECIFICATIONS

SERVICE INTERVALS

REPLACEMENT INTERVALS

CAPACITIES

FLUID CAPACITIES

SYSTEM REFRIGERANT CAPACITIES