ENGINE MECHANICAL
Note. The Assembly Line Data Link (ALDL) connector may also be referred to as the Data Link Connector (DLC) and the SERVICE ENGINE SOON (SES) light may also be referred to as the Malfunction Indicator Light (MIL).
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 A)
- 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 Malfunction Indicator Light (MIL) is off.
- Connect jumper between Data Link Connector (DLC) terminals "A" and "B". MIL should begin flashing. Connect timing light.
- Note average timing of cylinders No. 1 and 4 and adjust to specification, if necessary. See «4-CYLINDER IGNITION TIMING»(ref-19432-S15999308092001010200000) table. Remove jumper from DLC. Ensure MIL is off.
| Application | M/T | A/T |
|---|---|---|
| 2.5L (VIN A) | 8 @ Idle | 8 @ Idle |
4-CYLINDER IGNITION TIMING (DEGREES BTDC @ RPM)
Except 3.8L - VIN L
- 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 Malfunction Indicator Light (MIL) is off.
- 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.
- Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V6 IGNITION TIMING»(ref-19432-S32632367782001010200000) table. Reconnect EST by-pass connector, and clear ECM trouble code.
| Application | Man. Trans. | Auto. Trans. |
|---|---|---|
| 2.8L (VIN R) | 10 @ Idle | 10 @ Idle |
| 3.1L (VIN D) | 10 @ Idle | 10 @ Idle |
| 3.8L (VIN L) | (1) | (1) |
| 4.3L (VIN W & Z) | 0 @ Idle | 0 @ Idle |
| (1) Ignition timing is not adjustable (DIS). | ||
| (1) | Ignition timing is not adjustable (DIS). |
V6 IGNITION TIMING (DEGREES BTDC @ RPM)
V8 IGNITION TIMING
- 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 Malfunction Indicator Light (MIL) is not on.
- Disconnect Tan/Black Electronic Spark Timing (EST) by-pass connector wire located near distributor. DO NOT disconnect 4-wire connector at distributor.
- Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See «V8 IGNITION TIMING»(ref-19432-S13179443342001010200000) table. Reconnect EST by-pass connector, and clear ECM trouble code.
| 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 |
V8 IGNITION TIMING (DEGREES BTDC @ RPM)
6.2L & 6.5L
- 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).
- 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.
- 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. Both are controlled by 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 table. Minimum idle speed adjustment can only be performed on the 7.4L engines. See MINIMUM IDLE SPEED ADJUSTMENT (7.4L).
Controlled Idle Speed Check
- 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 Data Link Connector (DLC) with scan tester in Open Mode.
- 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»(ref-19432-S11852377262001010200000) table.
- If idle speed is not within specification, refer to TESTS W/O CODES article. On 7.4L engines, perform MINIMUM IDLE SPEED ADJUSTMENT below.
| 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 | 15-50 | |||
| "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 | |||
| Man. Trans. (3) | 600 | 5-30 | |||
| 5.7L TBI | |||||
| "C", "G", "K" & "P" Series | |||||
| Under 8500 GVW | |||||
| Auto. Trans. (2) | 550 | 5-30 | |||
| Man. Trans. (3) | 660 | 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 V6 & on 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. Tech 1 scan tester will display RDL with 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. | |||||
| (1) | Add 2 counts for engines with less than 500 miles. On 4.3L V6 & on 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. Tech 1 scan tester will display RDL with 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. |
CONTROLLED IDLE SPEED & IAC COUNT
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
- 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.
- 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.
- Adjust extended fast idle solenoid plunger by turning plunger hex head to obtain fast idle speed. See «IDLE SPEED (RPM)»(ref-19432-S00539095422001010200000) specifications table. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector.
| Application | Curb Idle | Fast Idle |
|---|---|---|
| 6.2L | 650 | 800 |
| 6.5L | 700 | 800 |
IDLE SPEED (RPM)
Scheme 1
THROTTLE POSITION (TP) SENSOR
Note. TP sensor is adjustable on diesel engines only. Resistance values given in TP SENSOR OUTPUT VOLTAGE (GASOLINE) table are for reference only. If resistance value is not as specified, replace TP sensor. For testing procedures, refer to appropriate TESTS W/CODES or SYSTEM & COMPONENT TESTING article.
| Application | (1) Volts |
|---|---|
| 2.5L (VIN A) | 1.25 or Less |
| 2.8L (VIN R) | .42-.45 |
| 3.1L (VIN D) | 1.25 Or Less |
| 4.3L (VIN W & Z) | 1.25 Or Less |
| 5.0L (VIN H) | 1.25 Or Less |
| 5.7L (VIN K) | 1.25 Or Less |
| 5.7L CNG (VIN K) | 1.25 Or Less |
| 7.4L (VIN N) | 1.25 Or Less |
| (1) At idle RPM or closed throttle. | |
| (1) | At idle RPM or closed throttle. |
TP SENSOR OUTPUT VOLTAGE (GASOLINE)
6.2L DIESEL LIGHT DUTY (VIN C)
- Remove air cleaner assembly and vacuum hoses. Disconnect TP sensor connector and install jumper wires between TPS and TPS harness connector. Turn ignition on, engine off.
- Install.646 Gauge Block (J-33043-2) between gauge boss on injection pump and WOT stop screw on throttle shaft. (Scheme 2)and (Scheme 3). Rotate throttle lever and hold the WOT stop screw against the gauge block.
- Using a DVOM, measure and record voltage between TP sensor connector terminals "A" and "C". This is TP sensor reference voltage. Measure and record voltage between TP sensor terminals "B" and "C". This is TP sensor voltage.
- TP sensor voltage should be within 3 volts of TP sensor reference voltage. If voltage reading is not within tolerance, adjust TP sensor.
- Loosen TP sensor mounting screws. Rotate TP sensor until correct sensor voltage is obtained. Tighten TP sensor mounting screws. Check TP sensor voltage by releasing throttle lever, allowing it to return to idle stop position. Check voltage reading between terminals "B" and "C".
- Return throttle lever against gauge block. Check voltage reading. Voltage should be less 2.2 volts at closed throttle and return to within.03 volts of adjusted voltage, when throttle is again opened against gauge block.
- If voltage reading does not return to TP sensor voltage, repeat steps 5) and 6). If voltage at closed throttle is not less than 2.2 volts or adjustment cannot be obtained, replace TP sensor.
- Turn ignition off. Remove gauge block, jumper wire and reconnect TP sensor harness connector. Reinstall air cleaner assembly.
6.2L DIESEL HEAVY DUTY (VIN J)
- Remove air cleaner assembly and vacuum hoses. Disconnect TP sensor connector and install jumper wires between TP sensor and TP sensor harness connector. Turn ignition on, engine off.
- Using a DVOM, measure and record voltage between TP sensor connector terminals "A" and "C". This is the TP sensor reference voltage. Perform the following calculations: Reference voltage x 0.33 = Desired TP sensor voltage setting. Record desired TP sensor voltage setting.
- Insert a.646" Gauge Block (J-33043-2) between gauge boss on pump and WOT stop screw on throttle lever. (Scheme 2)and (Scheme 3). Rotate throttle lever towards the WOT position, so gauge block is held firmly in place.
- Measure voltage between TP sensor terminals "B" and "C". This is TP sensor voltage. Voltage must be within 1 percent of the desired TP sensor voltage setting from step 2). If TP sensor voltage is within tolerance, proceed to step 6). If TP sensor voltage setting is not within tolerance, go to next step.
- To adjust TP sensor, loosen TP sensor mounting screws and rotate TP sensor until desired TP sensor voltage is obtained. Tighten TP sensor mounting screws and recheck voltage reading. Replace TP sensor assembly, if adjustment is not possible. NOTE: Switch point must be set only while rotating TP sensor body in clockwise direction.
- Release throttle lever and allow lever to return to idle position. Open throttle lever back against gauge block and check if TP sensor voltage is within TP sensor reference voltage, see step 2). If reading is not within tolerance, replace TP sensor assembly.
- Turn ignition off. Remove gauge block, jumper from TP sensor and wiring harness, and reconnect TP sensor harness connector. Reinstall air cleaner assembly.
Scheme 2
Scheme 3
6.5L TURBO DIESEL
See SERVICE MANUAL UPDATE 93-248-6C .
4.3L PFI (VIN Z)
- Remove passenger side wheelwell panel, retaining wire from actuator pin and boost control hose from wastegate actuator.
- Install Turbocharger Pressure Gauge (J-35691) to hose connection on wastegate actuator. Ensure dial reads zero.
- 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.
- 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.
- 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.