Engine Controls - Adjustments GMC Typhoon I

ENGINE MECHANICAL

Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.

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/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) . Remove jumper from ALDL connector. Ensure SERVICE ENGINE SOON light is off.

4-CYLINDER IGNITION TIMING (DEGREES BTDC @ RPM)

All Models (Except 3.8L VIN L)

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. On 4.3L, by-pass connector is on wiring harness conduit near distributor. On other models, by-pass connector is located near heater housing in passenger compartment. On all 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»(/gmc/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) . Reconnect EST by-pass connector, and clear ECM trouble code.

V6 IGNITION TIMING (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 not on.
2. Disconnect Tan/Black Electronic Spark Timing (EST) by-pass connector wire located 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/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) . Reconnect EST by-pass connector, and clear ECM trouble code.

V8 IGNITION TIMING (DEGREES BTDC @ RPM)

6.2L & 6.5L

1. Original factory injection pump timing is set by using static timing mark (a circle scribed across both pump flange and front housing) or static timing mark (straight line scribed across both pump flange and front housing). NOTE: A service/replacement pump will not be marked with dynamic timing mark (circle) and should be timed using the static timing mark (line).
2. To properly set timing, 2 halves of dynamic timing mark (circle) or static timing mark (line) must be aligned. Engine must not be running while injection timing is set.
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. 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.

Note. Controlled idle speed and IAC count can be checked using scan tester. See CONTROLLED IDLE SPEED & IAC COUNT . Minimum idle speed adjustment can only be performed on the 7.4L engines. See MINIMUM IDLE SPEED ADJUSTMENT (7.4L ONLY) heading below.

Controlled Idle Speed Check

1. Ensure no trouble code(s) are present, IAC system has been checked and ignition timing is correct. Block drive wheel and apply parking brake. Connect scan tester to ALDL connector with scan tester in "Open Mode".
2. Start engine and bring to normal operating temperature. Check for correct state of Park/Neutral switch on scan tester. Check if idle speed and IAC valve pintle position (counts) are as specified. See «CONTROLLED IDLE SPEED & IAC COUNT»(/gmc/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) .
3. If idle speed is not within specification, refer to TESTS W/O CODES article in this section. On 7.4L engines, perform MINIMUM IDLE SPEED ADJUSTMENT. See MINIMUM IDLE SPEED ADJUSTMENT (7.4L ONLY) heading below.

CONTROLLED IDLE SPEED & IAC COUNT

Minimum Idle Speed Adjustment (7.4L Only)

1. Check controlled idle speed and perform IAC system check first. Refer to CONTROLLED IDLE SPEED CHECK heading above. 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/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) . 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 normal operating temperature. Install Tachometer (J-26925). Ensure air cleaner is in place and all accessories are turned off. Adjust curb (low) 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 normal operating temperature. Install Tachometer (J-26925). Ensure air cleaner is in place and all accessories must 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 fast idle solenoid plunger.
3. Adjust extended fast idle solenoid plunger by turning plunger hex head to obtain fast idle speed. See «IDLE SPEED (RPM)»(/gmc/typhoon/i-1991-1993/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

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 are for reference only. If resistance value is not as specified, replace TPS. For testing procedures, refer to appropriate G - TESTS W/ CODES I - SYS/COMP TESTS article in this section.

2.8L (VIN R)

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 switch 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/typhoon/i-1991-1993/remont/adjustments/#engine-controls-adjustments) . 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 (GASOLINE)

6.2L Light Duty (VIN C)

1. Remove air cleaner assembly and vacuum hoses. Disconnect TPS connector and install jumper wires between TPS and TPS harness connector. Turn ignition on, engine off.
2. Install.646 Gauge Block (J-33043-2) between gauge boss on injection pump and WOT stop screw on throttle shaft. (Scheme 2) Rotate throttle lever and hold the WOT stop screw against the gauge block.
3. Using a DVOM, measure and record voltage between TPS connector terminals "A" and "C". This is the TPS reference voltage. Measure and record voltage between TPS terminals "B" and "C". This is TPS voltage.
4. The TPS voltage should be within +/-3 volts of TPS reference voltage. If voltage reading is not within tolerance, adjust TPS.
5. Loosen TPS mounting screws. Rotate TPS until the correct TPS voltage is obtained. Tighten TPS mounting screws. Check TPS voltage by releasing throttle lever, allowing it to return to idle stop position. Check voltage reading between terminals "B" and "C".
6. Return throttle lever against gauge block. Check voltage reading. Voltage should be less 2.2 volts at closed throttle and return to +/-.03 volts of adjusted voltage, when throttle is again opened against gauge block.
7. If voltage reading does not return to TPS voltage, repeat steps 5) and 6). If voltage at closed throttle is not less than 2.2 volts or adjustment cannot be obtained, replace TPS.
8. Turn ignition off. Remove gauge block, jumper wire and reconnect TPS harness connector. Reinstall air cleaner assembly.

6.2L Heavy Duty (VIN J)

1. Remove air cleaner assembly and vacuum hoses. Disconnect TPS connector and install jumper wires between TPS and TPS harness connector. Turn ignition on, engine off.
2. Using a DVOM, measure and record voltage between TPS connector terminals "A" and "C". This is the TPS reference voltage. Perform the following calculations: Reference voltage x 0.33 = Desired TPS voltage setting. Record the desired TPS voltage setting.
3. Insert a.646" Gauge Block (J-33043-2) between gauge boss on pump and WOT stop screw on throttle lever. (Scheme 2) Rotate throttle lever towards the WOT position, so gauge block is held firmly in place.
4. Measure voltage between TPS terminals "B" and "C". This is the TPS voltage. Voltage must be within +/-1 percent of the desired TPS voltage setting from step 2). If TPS voltage is within tolerance, proceed to step 6). If TPS voltage setting is not within tolerance, go to next step.
5. To adjust TPS, loosen TPS mounting screws and rotate TPS until desired TPS voltage is obtained. Tighten TPS mounting screws and recheck voltage reading. Replace TPS assembly, if adjustment is not possible. NOTE: Switch point must be set only while rotating TPS body in clockwise direction.
6. Release throttle lever and allow lever to return to idle position. Open throttle lever back against gauge block and check if TPS voltage is within TPS reference voltage, see step 2). If reading is not within tolerance, replace TPS assembly.
7. Turn ignition off. Remove gauge block, jumper from TPS and wiring harness, and reconnect TPS harness connector. Reinstall air cleaner assembly.

Scheme 2

Scheme 3

WASTEGATE ACTUATOR ADJUSTMENT (TURBO)

4.3L PFI (VIN Z)

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" (0.5-1.5 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:
• 4-CYLINDER IGNITION TIMING