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.
V6 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 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-19725-S22713567272001010200000) . Reconnect EST by-pass connector, and clear ECM trouble code.
| Application | Man. Trans. | Auto. Trans. |
|---|
| 4.3L (VIN W & Z) (1) | 0 @ Idle | 0 @ Idle |
| (1) Ignition timing is not adjustable with DIS. |
| (1) | Ignition timing is not adjustable with 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-19725-S00469268702001010200000) . 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)
IDLE SPEED & MIXTURE
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 . Minimum idle speed adjustment can only be performed on the 7.4L engines. See the MINIMUM IDLE SPEED ADJUSTMENT (7.4L) heading below.
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-19725-S09043712412001010200000) .
- If idle speed is not within specification, refer to appropriate «TESTS W/O CODES - GASOLINE»(ref-19726) article in the ENGINE PERFORMANCE section. On 7.4L engines, perform MINIMUM IDLE SPEED ADJUSTMENT.
| Application | Idle RPM | (1) IAC Counts |
|---|
| 4.3L TBI |
| "C" & "K" Series |
| Auto. Trans. (2) (4) | 537 | 5-30 |
| Auto. Trans. (2) | 650 | 20-35 |
| Man. Trans. (3) | 550 | 2-20 |
| 5.0L TBI |
| "C" & "K" Series |
| Auto. Trans. (2) | 500 | 5-30 |
| Man. Trans. (3) | 600 | 5-30 |
| 5.7L TBI |
| "C" & "K" 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" &"K" |
| 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 and V8 engines, add 2 counts 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) Calibration identification is 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 and V8 engines, add 2 counts 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) | Calibration identification is not given by manufacturer. IAC count and actual RPM should correspond to one of these calibrations. |
CONTROLLED IDLE SPEED & IAC COUNT
THROTTLE POSITION (TP) SENSOR
| Application | (1) Volts |
|---|
| 4.3L (VIN W & Z) | .85 Or Less |
| 5.0L (VIN H) | .85 Or Less |
| 5.7L (VIN K) | .85 Or Less |
| 5.7L CNG (VIN K) | .85 Or Less |
| 7.4L (VIN N) | .85 Or Less |
| (1) At idle RPM or closed throttle. |
| (1) | At idle RPM or closed throttle. |
