IGNITION TIMING (GASOLINE) 4-CYLINDER IGNITION TIMING 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 table. Remove jumper from ALDL connector. Ensure SERVICE ENGINE SOON light is off. 4-CYLINDER IGNITION TIMING Application Man. Trans. Auto. Trans. 2.5L (VIN E) 8 @ Idle 8 @ Idle V6 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 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 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. Saturday, April 12, 2008 12:24:03 AM
3. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See V6 IGNITION TIMING table. Reconnect EST by-pass connector, and clear ECM trouble code. V6 IGNITION TIMING Application Man. Trans. Auto. Trans. 2.8L (VIN R) 10 @ Idle 10 @ Idle 3.1L (VIN D) 10 @ Idle 10 @ Idle 4.3L (VIN Z) Non-Turbo 0 @ Idle 0 @ Idle Turbo (1) (1) (1) Information not available from manufacturer. V8 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 table. Reconnect EST by-pass connector, and clear ECM trouble code. V8 IGNITION TIMING Application Man. Trans. Auto. Trans. 5.0L (VIN H) 0 @ Idle 0 @ Idle 5.7L (VIN K) 0 @ Idle 0 @ Idle 7.4L (VIN N) 4 @ Idle 4 @ Idle 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. CONTROLLED IDLE SPEED & IAC COUNT Application Idle RPM (1) IAC Counts 2.5L TBI "S" Series Page 2
Auto. Trans. (2) 800 15-40 Man. Trans. (3) 900 5-20 2.8L TBI "S" Series Auto. Trans. (2) 800 5-20 3.1L TBI "U" Series Auto. Trans. (2) 600-700 5-15 3.8L PFI "U" Series Auto. Trans. (2) 650-750 16-20 4.3L CPI "L" Series Auto. Trans. (2) 625 5-50 "M", "S" & "T" Series Auto. Trans. (2) 550 5-40 4.3L PFI Turbo "S" & "T" Series Auto. Trans. (2) (4) 1-50 4.3L TBI "C" & "K" Series Auto. Trans. (2)(5) 537 5-30 Auto. Trans. (2)(5) 650 20-35 Man. Trans. (3) 550 2-20 "G" Series Auto. Trans. (2) 538 5-30 Man. Trans. (3) 650 5-30 "L" Series Auto. Trans. (2) 625 5-50 Man. Trans. (3) 600 3-30 "M" Series Auto. Trans. (2) 538 5-30 "P" Series Auto. Trans. (2) 650 20-35 5.0L TBI "C" & "K" Series Auto. Trans. (2) 500 5-30 Page 3
Man. Trans. (3) 600 5-30 5.7L TBI "C", "G", "K" & "P" Series Under 8500 GVW Auto. Trans. (2) 525 5-30 Man. Trans. (3) 600 5-30 Over 8500 GVW Auto. Trans. (2) 550 5-30 Man. Trans. (3) 600 5-30 7.4L TBI "C", "G", "K" & "P" Series Auto. Trans. (2) 750 5-30 Man. Trans. (3) 800 5-30 (1) Add 2 counts for engines with less than 500 miles. On 4.3L & V8 engines, add 2 counts for every 1000 ft. above sea level. On 2.5L & 2.8L engines, add 1 count for every 1000 ft. above sea level. (2) Automatic transmission in Drive. (3) Manual transmission in Neutral. (4) Set to +/-50 RPM from desired idle speed in Drive. (5) Calibration identification not given by manufacturer. IAC count and actual RPM should correspond to one of these calibrations. 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 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. Page 4
MINIMUM IDLE SPEED (1) Application 7.4L RPM Auto. Trans. (2) 600-650 Man. Trans. (3) 675-725 (1) Idle speed with seated IAC is lower than specified, if engine has less than 500 miles or when checked at altitudes above 1500 feet. (2) Automatic transmission in Drive. (3) Manual transmission in Neutral. IDLE SPEED (DIESEL) 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. See Fig. 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. See Fig. 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) specifications table. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector. IDLE SPEED (RPM) Application Curb Idle Fast Idle 6.2L 650 800 Page 5
Fig. 1: Adjusting Idle Speed (Diesel) Courtesy of GENERAL MOTORS CORP. 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. THROTTLE POSITION SENSOR (TPS) Page 6
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 G - TESTS W/CODES - GASOLINE or I - SYSTEM/COMPONENT 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 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 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 Application (1) Voltage 2.5L (VIN E) (2) 1.25 or less 2.8L (VIN R).42-.45 3.1L (VIN D) (2) 1.25 Or Less 4.3L (VIN Z) (2) 1.25 Or Less 5.0L (VIN H) (2) 1.25 Or Less 5.7L (VIN K) (2) 1.25 Or Less 7.4L (VIN N) (2) 1.25 Or Less (1) At idle RPM or closed throttle. (2) Not adjustable. TPS ADJUSTMENT (DIESEL) 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. Page 7
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). See Fig. 2. 4) Insert a.646" Gauge Block (J-33043-A) between gauge boss on pump and WOT stop screw on throttle lever. See Fig. 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. See Fig. 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. See Fig. 3. Test light should not illuminate. If test light illuminates, TPS is not adjusted properly. Repeat step 1). TPS ADJUSTMENT SPECIFICATIONS Application TPS Voltage Ratio 6.2L Light Duty (VIN C).15-.30 Heavy Duty (VIN J) (1) (1) Test light is used to check TPS adjustment. Page 8
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Fig. 2: Adjusting TPS (6.2L Light Duty - VIN C) Courtesy of GENERAL MOTORS CORP. Page 10
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Fig. 3: Adjusting TPS (6.2L Heavy Duty - VIN J) Courtesy of GENERAL MOTORS CORP. 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). See Fig. 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. See Fig. 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. Page 12
Fig. 4: Adjusting Vacuum Regulator Valve & Detent Switch Courtesy of GENERAL MOTORS CORP. WASTEGATE ACTUATOR ADJUSTMENT (TURBO) Page 13
CAUTION: Improper wastegate actuator adjustment can severely limit performance or cause overboost, resulting in fuel shutoff. 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. COMPRESSION SPECIFICATIONS Application Compression Ratio 2.5L (VIN E) 8.3:1 2.8L (VIN R) 8.9:1 3.1L (VIN D) 8.9:1 4.3L (VIN Z) Non-Turbo (1) 9.3:1 Turbo 8.35:1 5.0L (VIN H) 9.3:1 5.7L (VIN K) (2) 9.1:1 6.2L Diesel (VIN C & J) 21.3:1 7.4L (VIN N) 7.9:1 Gasoline Engines Min. Compression Pressure 100 psi (7 kg/cm 2 ) Max. Variation Between Cylinders Less Than 30% Diesel Engines Compression Pressure 380-400 psi (27-28 kg/cm 2 ) Max. Variation Between Cylinders 20% (1) Heavy duty: 8.6:1. (2) Over 8500 lbs. GVW: 8.3:1. V6 IGNITION TIMING Application Man. Trans. Auto. Trans. Page 14
2.8L (VIN R) 10 @ Idle 10 @ Idle 3.1L (VIN D) 10 @ Idle 10 @ Idle 4.3L (VIN Z) Non-Turbo 0 @ Idle 0 @ Idle Turbo (1) (1) (1) Information not available from manufacturer. CONTROLLED IDLE SPEED & IAC COUNT Application Idle RPM (1) IAC Counts 2.5L TBI "S" Series Auto. Trans. (2) 800 15-40 Man. Trans. (3) 900 5-20 2.8L TBI "S" Series Auto. Trans. (2) 800 5-20 3.1L TBI "U" Series Auto. Trans. (2) 600-700 5-15 3.8L PFI "U" Series Auto. Trans. (2) 650-750 16-20 4.3L CPI "L" Series Auto. Trans. (2) 625 5-50 "M", "S" & "T" Series Auto. Trans. (2) 550 5-40 4.3L PFI Turbo "S" & "T" Series Auto. Trans. (2) (4) 1-50 4.3L TBI "C" & "K" Series Auto. Trans. (2)(5) 537 5-30 Auto. Trans. (2)(5) 650 20-35 Man. Trans. (3) 550 2-20 "G" Series Auto. Trans. (2) 538 5-30 650 5-30 Page 15
Man. Trans. (3) "L" Series Auto. Trans. (2) 625 5-50 Man. Trans. (3) 600 3-30 "M" Series Auto. Trans. (2) 538 5-30 "P" Series Auto. Trans. (2) 650 20-35 5.0L TBI "C" & "K" Series Auto. Trans. (2) 500 5-30 Man. Trans. (3) 600 5-30 5.7L TBI "C", "G", "K" & "P" Series Under 8500 GVW Auto. Trans. (2) 525 5-30 Man. Trans. (3) 600 5-30 Over 8500 GVW Auto. Trans. (2) 550 5-30 Man. Trans. (3) 600 5-30 7.4L TBI "C", "G", "K" & "P" Series Auto. Trans. (2) 750 5-30 Man. Trans. (3) 800 5-30 (1) Add 2 counts for engines with less than 500 miles. On 4.3L & V8 engines, add 2 counts for every 1000 ft. above sea level. On 2.5L & 2.8L engines, add 1 count for every 1000 ft. above sea level. (2) Automatic transmission in Drive. (3) Manual transmission in Neutral. (4) Set to +/-50 RPM from desired idle speed in Drive. (5) Calibration identification not given by manufacturer. IAC count and actual RPM should correspond to one of these calibrations. MINIMUM IDLE SPEED (1) Application 7.4L RPM Auto. Trans. (2) 600-650 Man. Trans. (3) 675-725 Page 16
(1) Idle speed with seated IAC is lower than specified, if engine has less than 500 miles or when checked at altitudes above 1500 feet. (2) Automatic transmission in Drive. (3) Manual transmission in Neutral. IDLE SPEED (RPM) Application Curb Idle Fast Idle 6.2L 650 800 TPS OUTPUT VOLTAGE Application (1) Voltage 2.5L (VIN E) (2) 1.25 or less 2.8L (VIN R).42-.45 3.1L (VIN D) (2) 1.25 Or Less 4.3L (VIN Z) (2) 1.25 Or Less 5.0L (VIN H) (2) 1.25 Or Less 5.7L (VIN K) (2) 1.25 Or Less 7.4L (VIN N) (2) 1.25 Or Less (1) At idle RPM or closed throttle. (2) Not adjustable. TPS ADJUSTMENT SPECIFICATIONS Application TPS Voltage Ratio 6.2L Light Duty (VIN C).15-.30 Heavy Duty (VIN J) (1) (1) Test light is used to check TPS adjustment. Page 17