Engine Controls - Adjustments: Other Chevrolet Sportvan G20

ENGINE COMPRESSION

Note. On diesel engines, DO NOT add oil to cylinders during compression check, as extensive engine damage will result.

Check engine compression pressure with engine at normal operating temperature.

On gasoline engines, remove all spark plugs. Ensure throttle plates are wide open and battery is fully charged. Remove fuel pump or ECM fuse. Disconnect battery terminal from HEI distributor. Crank engine through at least 4 compression strokes.

On diesel engines, remove air cleaner. Install Intake Manifold Cover (J-29664-2) over intake manifold opening. Disconnect wire from injection pump shutoff solenoid. Disconnect glow plug wiring and remove all glow plugs. Use Compression Gauge (J-26999-10) to test individual cylinders. Crank engine through at least 6 compression strokes.

On gasoline engines, the lowest cylinder reading should NOT be less than 70 percent (80 percent on diesel engines) of the highest cylinder reading. No cylinder reading should be less than 100 psi (7 kg/cm 2 ).

COMPRESSION SPECIFICATIONS

VALVE CLEARANCE

Note. All models use hydraulic lifters. No adjustments are required.

2.5L (VIN E)

1. Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
2. Ground terminals "A" and "B" at ALDL connector. SERVICE ENGINE SOON light should begin flashing. Connect timing light.
3. Set average timing of cylinders No. 1 and No. 4 to specification and adjust if necessary. See «4-CYLINDER IGNITION TIMING SPECIFICATIONS»(ref-10145-S42175651742001010200000) table. Remove jumper from ALDL connector. Ensure SERVICE ENGINE SOON light is off.

4-CYLINDER IGNITION TIMING SPECIFICATIONS (Degrees BTDC @ RPM)

2.8L (VIN R)

1. Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
2. Disconnect Tan/Black wire EST by-pass connector located near heater housing in engine compartment on S/T Series, or near distributor on all other V6 models. DO NOT disconnect 4-wire connector at distributor.
3. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V6 IGNITION TIMING SPECIFICATIONS»(ref-10145-S20036877622001010200000) table. Reconnect EST by-pass connector and clear ECM trouble code.

3.1L (VIN D)

1. Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
2. Disconnect and ground Tan/Black wire EST by-pass connector located in front of right strut tower. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. Refer to the «V6 IGNITION TIMING SPECIFICATIONS»(ref-10145-S20036877622001010200000) table.
3. Disconnect ground from EST by-pass circuit and reconnect connector. Clear ECM trouble code.

4.3L (VIN Z)

1. Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
2. Disconnect Tan/Black wire EST by-pass connector located near heater housing in engine compartment on S/T Series, or near distributor on all other V6 models. DO NOT disconnect 4-wire connector at distributor.
3. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V6 IGNITION TIMING SPECIFICATIONS»(ref-10145-S20036877622001010200000) table. Reconnect EST by-pass connector and clear ECM trouble code.

V6 IGNITION TIMING SPECIFICATIONS (Degrees BTDC @ RPM)

ALL MODELS (EXCEPT DIESEL)

1. Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
2. Disconnect Tan/Black wire EST by-pass connector located behind electrical junction box cover or near distributor. DO NOT disconnect 4-wire connector at distributor.
3. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V8 IGNITION TIMING SPECIFICATIONS»(ref-10145-S08333950662001010200000) table. Reconnect EST by-pass connector and clear ECM trouble code.

V8 IGNITION TIMING SPECIFICATIONS (Degrees BTDC @ RPM)

6.2L (VIN C & J)

1. Original factory injection pump timing is marked with a static timing mark (straight line scribed across both the pump flange and front housing). Injection pump timing is dynamically checked and marked with a dynamic timing mark (a circle scribed across both the pump flange and the front housing).
2. To properly time engine, the 2 halves of the dynamic timing mark (circle between pump flange and front housing) must be aligned. Engine must be off while timing is being set. Service pump is not marked with dynamic timing mark (circle) and should be timed using static timing mark.
3. Check alignment of injection pump timing marks on top of engine front cover and injection pump flange. If timing marks are not aligned, loosen 3 retaining nuts and align mark on injection pump with mark on front cover. Tighten nuts to 30 ft. lbs. (41 N.m). Adjust throttle linkage.

IDLE SPEED & MIXTURE (GASOLINE)

Note. Idle mixture and idle speed is controlled by the Electronic Control Module (ECM). DO NOT attempt to adjust them. Incorrect idle speeds are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.

CURB IDLE

Set parking brake and block drive wheels. Warm engine to operating temperature. Install Tachometer (J-26925). Air cleaner must be in place and accessories turned off. Adjust low idle speed to specifications by turning low speed idle screw on pump. Refer to the IDLE SPEED (RPM) SPECIFICATIONS table.

FAST IDLE

1. Set parking brake and block drive wheels. Warm engine to operating temperature. Install Tachometer (J-26925). Air cleaner must be in place and all accessories turned off.
2. Remove connector from fast idle solenoid. To energize solenoid, connect jumper wire from battery positive terminal to solenoid terminal. Open throttle to ensure plunger is fully extended.
3. Adjust fast idle speed by turning plunger hex head. Adjust to specifications. See «IDLE SPEED (RPM) SPECIFICATIONS»(ref-10145-S22005110762001010200000) table. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector.

Scheme 2

IDLE SPEED (RPM) SPECIFICATIONS

PURGING FUEL SYSTEM (DIESEL)

Note. If vehicle is equipped with dual tanks, perform purging procedure on each tank.

1. Park vehicle on a level surface. Place drain pan under drain hose. Open drain valve 3-4 turns. With fuel tank cap installed and using air nozzle, apply 3-5 psi (.21-.35 kg/cm 2 ) through fuel return hose at injection pump.
2. Contaminated fuel will be forced out of tank via filter drain hose. Continue to drain fuel until clear fuel is observed. Entire fuel tank may have to be drained. Close drain valve. Install fuel return hose.

Throttle Position Sensor (TPS) can also be adjusted with the use of Scan tester. This check should be performed only when throttle body parts have been replaced or after minimum airflow has been adjusted.

1) Install 3 jumper wires between TPS and TPS wiring harness connector. Jumpers can be made using the following General Motors' parts: Terminals No. 1214836 and 12014837.

2) Turn ignition to ON position. DO NOT start engine. Use digital voltmeter and connect to Dark Blue and Black wire terminals. With throttle at closed position, TPS voltage should be between .42-.45 volt.

3) If voltage reading is not as specified, rotate TPS until specified voltage is obtained. See TPS OUTPUT VOLTAGE table. If specified voltage cannot be obtained, replace TPS.

4) Tighten screws and recheck readings. Turn ignition off. Remove jumper wires and reconnect harness connector to TPS.

TPS OUTPUT VOLTAGE