Engine Controls - Adjustments GMC Sonoma Syclone

ENGINE COMPRESSION

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 primary lead to distributor or ignition coil. Crank engine through at least 4 compression strokes. The lowest cylinder reading should NOT be less than 70 percent of the highest cylinder reading. No cylinder reading should be less than 100 psi (7 kg/cm 2 ).

On diesel engines, remove air cleaner. Install Intake Manifold Cover (J-29664-2 or J-26996-1) over intake manifold opening. Disconnect Pink wire from injection pump shutoff solenoid. Disconnect glow plug wiring and remove all glow plugs. Use Compression Gauge (J-26999) to test individual cylinders. Crank engine through at least 6 compression strokes. The lowest cylinder reading should NOT be less than 80 percent of the highest cylinder reading. No cylinder reading should be less than 380 psi (27 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. Connect jumper between ALDL connector terminals "A" and "B". SERVICE ENGINE SOON light should begin flashing. Connect timing light.
3. Note average timing of cylinders No. 1 and 4 and adjust to specification if necessary. See «4-CYLINDER IGNITION TIMING»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) table. Remove jumper from ALDL connector. Ensure SERVICE ENGINE SOON light is off.

4-CYLINDER IGNITION TIMING

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 Electronic Spark Timing (EST) by-pass connector wire located near heater housing in passenger compartment. 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»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) 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. Ground Tan/Black Electronic Spark Timing (EST) by-pass connector wire located in front of right strut tower. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V6 IGNITION TIMING»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) 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 Electronic Spark Timing (EST) by-pass connector wire located near heater housing in engine compartment or near distributor or near electrical junction box cover. 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»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) table. Reconnect EST by-pass connector, and clear ECM trouble code.

V6 IGNITION TIMING

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 Electronic Spark Timing (EST) by-pass connector wire 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»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) table. Reconnect EST by-pass connector, and clear ECM trouble code.

V8 IGNITION TIMING

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 set timing, 2 halves of dynamic timing mark (circle between pump flange and front housing) must be aligned. Engine must not be running while injection timing is set. A service/replacement pump will not be 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.

GASOLINE

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

CONTROLLED IDLE SPEED & IAC COUNT

Minimum Idle Speed Adjustment (7.4L Only)

1. Check controlled idle speed and perform IAC system check first. Set parking brake and block drive wheels. Start engine and operate to normal operating temperature, about 185-212°F (85-100°C). Turn engine off.
2. Remove air cleaner, adapter and gaskets. Ensure that throttle lever is not binding TV or cruise control cables. Using a jumper, ground ALDL diagnostic connector. Turn ignition on (engine off). Wait for at least 10 seconds (this allows IAC pintle to extend and seat in throttle body).
3. Disconnect IAC harness connector. Remove jumper from ALDL diagnostic connector. Connect scan tester to ALDL diagnostic connector. Place scan tester in "Open Mode". Place transmission in Neutral. Start engine and allow engine RPM to stabilize. Check engine RPM. See «MINIMUM IDLE SPEED»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) table. Disregard IAC count on scan tester with IAC disconnected.
4. If idle speed is not as specified, remove stop screw plug by using an awl. With engine at normal operating temperature, adjust stop screw to obtain nominal RPM with seated IAC valve. Turn ignition off. Reconnect IAC harness connector. Disconnect scan tester. Reseal stop screw hole and reinstall air cleaner assembly.
5. Reset IAC valve. To reset IAC valve, turn ignition on (engine off) for 5 seconds. Turn ignition off for 10 seconds. Start engine and check for proper idle operation. Repeat procedure if proper idle operation is not obtained.

MINIMUM IDLE SPEED (1)

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 curb idle speed to specifications by turning curb idle speed screw on fuel injection pump. (Scheme 1) See 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. (Scheme 1) To energize solenoid, connect jumper wire from battery positive terminal to fast idle solenoid terminal. Open throttle momentarily to energize and fully extend the fast idle solenoid plunger.
3. Adjust the extended fast idle solenoid plunger by turning plunger hex head to obtain the fast idle speed. See «IDLE SPEED (RPM)»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) specifications table. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector.

IDLE SPEED (RPM)

Scheme 1

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 flowing through drain hose. Entire fuel tank may need to be drained. Close drain valve. Install fuel return hose.

TPS ADJUSTMENT (GASOLINE)

Note. On all models except 2.8L engine (VIN R), Throttle Position Sensor (TPS) is NOT adjustable. Resistance values given in TPS OUTPUT VOLTAGE TABLE are for reference only. If resistance value is not as specified, replace TPS. For testing procedures, refer to TESTS W/CODES - GASOLINE or SYSTEM/COMPONENT TESTS article in this section.

Throttle Position Sensor (TPS) can also be adjusted using a Scan tester. Perform this check 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. Using a DVOM, connect test leads to Dark Blue and Black wire terminals. With throttle at closed position, TPS voltage should be .42-.45 volt.
3. If voltage reading is not as specified, rotate TPS until specified voltage is obtained. See «TPS OUTPUT VOLTAGE»(/gmc/sonoma-syclone/1991-1992/remont/adjustments/#engine-controls-adjustments) 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

6.2L LIGHT DUTY (VIN C)

1. Using a DVOM, measure and record resistance of power supply voltage. This is the reference voltage. Perform the following calculations: Reference voltage x 0.63 = Desired signal voltage. Reference voltage x 0.01 = Signal voltage tolerance.

Record the desired signal voltage and signal voltage tolerance.

2) With throttle lever in the closed position, loosen throttle position sensor to injector pump screws.

3) Connect power supply across TPS ground wire (Black) and reference wire (Gray). Connect DVOM across ground wire (Black) and signal wire (Blue). (Scheme 2)

4) Insert a.646" Gauge Block (J-33043-A) between gauge boss on pump and WOT stop screw on throttle lever. (Scheme 2) Rotate TPS clockwise until DVOM reads the desired signal voltage as determined in step 1). Tighten TPS mounting screws to 53 INCH lbs. (6 N.m).

5) Release throttle lever and allow it to return to idle position. At idle, DVOM should read a voltage ratio of .15-.30 volts. If voltage ratio is not .15-.30 volts, check for a faulty sensor.

6) Rotate throttle lever against gauge block, and recheck desired signal voltage tolerance, determined in step 1). Repeat step 2), if readjustment is required.

6.2L HEAVY DUTY (VIN J)

1. Disconnect TPS electrical connector. With throttle closed, loosen TPS mounting screws. Connect test light across TPS connector. Insert.280" Gauge Block (J-33043-A) between gauge boss and WOT stop screw on throttle shaft. (Scheme 3)
2. Rotate and hold throttle lever against gauge block. Rotate TPS clockwise until test light illuminates. Tighten TPS mounting screws. NOTE: Switch point must be set only while rotating TPS body in clockwise direction.
3. Release throttle lever and allow to return to idle position. Remove.280" Gauge Block (J-33043-A). Insert a.310" Gauge Block (J-33043-A) between throttle lever and fast idle screw. (Scheme 3) Test light should not illuminate. If test light illuminates, TPS is not adjusted properly. Repeat step 1).

TPS ADJUSTMENT SPECIFICATIONS

Scheme 2

Scheme 3

VACUUM REGULATOR VALVE/ DETENT SWITCH ADJUSTMENT (DIESEL)

1. Loosen vacuum regulator valve so it is free to rotate on pump. Attach a hand-held vacuum pump and apply 20 in. Hg to bottom port of valve. Attach vacuum gauge to top port of valve.
2. Insert 0.646" Gauge Block (J-33043) between gauge boss on injection pump and wide open stop screw on throttle lever (switch on position). (Scheme 4) NOTE: Always refer to underhood Emission Control Label for correct gauge block size.
3. Rotate and hold throttle shaft against gauge block. Slowly rotate vacuum regulator valve body clockwise (facing valve) until vacuum gauge reads 10.9-12.1 in. Hg. Hold valve body at this position and tighten mounting screws.
4. Check adjustment by allowing throttle shaft to return to idle stop position, then rotate throttle shaft back against gauge block. Vacuum gauge reading must be 10.9-12.1 in. Hg. If vacuum is not within limits, reset valve.
5. With vacuum valve set, confirm detent switch point by reading resistance between ignition (Pink/Black wire) and detent terminal (Orange wire). Insert Switch Gauge (J-36142) between wide open stop pin and wide open stop screw on throttle lever. (Scheme 4)
6. Rotate throttle lever against switch gauge. Continuity should NOT be present. Release throttle lever and remove gauge. Rotate throttle lever to wide open throttle (lever stop screw touching pump stop pin).
7. Check switch for continuity. Switch must have less than one ohm resistance before throttle reaches wide open position. If switch does not meet specification, reset assembly by returning to step 1) and repeating entire procedure.

Scheme 4

WASTEGATE ACTUATOR ADJUSTMENT (TURBO)

1. Remove passenger side wheelwell panel, retaining wire from actuator pin and boost control hose from wastegate actuator.
2. Install Turbocharger Pressure Gauge (J-35691) to hose connection on wastegate actuator. Ensure dial reads zero.
3. Install Dial Indicator (J-8001-3) on end of wastegate actuator lever. Ensure dial reads zero. Apply 4.5-5.0 psi (.31-.35 kg/cm 2 ) air pressure to Pressure Gauge (J-35691). Check dial indicator.
4. If dial indicator reads greater than 0.02-0.06" (0.5-1.5 mm), readjust rod by shortening it a half-turn at rod end. If dial indicator reads less than 0.02-0.06" (0.02-0.06 mm), readjust rod by lengthening it a half-turn at rod end.
5. Recheck actuator travel at 4.5-5.0 psi (.31-.35 kg/cm 2 ) air pressure. Repeat adjustment until specifications are met. Replace wastegate actuator if specifications cannot be met or if wastegate does not open at all.

See also:
• TESTS W/CODES - GASOLINE
• SYSTEM/COMPONENT TESTS
• 4-CYLINDER IGNITION TIMING