ENGINE MECHANICAL
Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.
VALVE CLEARANCE
Note. All engines use hydraulic lifters. No adjustments are required.
ALL ENGINES EXCEPT 3.3L
| CAUTION | Timing light secondary connection should be made with inductive pick-up. DO NOT puncture cables, boots or nipples with test probes. |
- Connect a suitable timing light to No. 1 cylinder. Refer to equipment manufacturer's instructions for proper connection. Turn selector switch to the appropriate cylinder position.
- Start engine and warm to normal operating temperature. Connect tachometer and ensure idle RPM is within specification. See «CURB IDLE SPEED (RPM)»(ref-10637-S38209934892000111000000) table under IDLE SPEED & MIXTURE. Disconnect engine coolant sensor lead wire. Radiator fan should come on and CHECK ENGINE light should illuminate.
- Check timing through timing window in bellhousing on 4-cylinder models or crankshaft pulley for other engines. See IGNITION TIMING table. DO NOT adjust timing if it is within 2 degrees of specification. If timing is incorrect, loosen distributor hold-down bolt and turn housing until specified timing is obtained.
- Recheck timing after tightening distributor hold-down bolt. Reconnect coolant lead wire. Erase any fault codes. Recheck curb idle and adjust (if necessary). Remove diagnostic equipment.
| Application | Man. Trans. | Auto. Trans. |
|---|---|---|
| 2.5L | 10-14 @ 850 | 10-14 @ 850 |
| 3.0L | N/A | 10-14 @ 700 |
| 3.3L | N/A | 14-18 @ 750 |
| 3.9L, 5.2L & 5.9L | (1) 8-12 | (1) 8-12 |
| (1) At idle. | ||
| (1) | At idle. |
IGNITION TIMING (Degrees BTDC @ RPM)
IDLE SPEED & MIXTURE
Note. Mixture is controlled by Single Board Engine Controller (SBEC). No adjustment is possible.
MINIMUM AIRFLOW
Note. Minimum airflow testing procedures are provided for 2.5L, 3.0L, 3.3L & 3.9L engines equipped with Automatic Idle Speed (AIS) motor on throttle body.
- Warm engine to normal operating temperature. Disconnect and plug heated air door vacuum hose. Connect timing light and tachometer. Disconnect engine coolant temperature sensor. Set basic timing to 10-14 degrees BTDC. Turn engine off. Reconnect coolant temperature sensor.
- With engine off, disconnect hose from PCV valve, and plug PCV valve nipple. Disconnect idle purge hose from vacuum harness "T". (Scheme 1) Attach Air Metering Fitting (6457) to manifold-mounted idle purge hose. Orifice size is.125" (3 mm). Connect Diagnostic Readout Box II (DRB-II) to vehicle.
- Start engine. Let engine idle for at least one minute. Using DRB-II, access MINIMUM AIRFLOW IDLE SPEED. When this mode is accessed, AIS motor will fully close, spark advance will fix, fuel delivery will not change and engine RPM will be displayed on DRB-II.
- Check minimum airflow. See MINIMUM AIRFLOW IDLE SPEED table. If minimum airflow idle speed is not within specification, replace throttle body.
Scheme 1
| Application | RPM |
|---|---|
| 2.5L | 1050-1250 |
| 3.0L | 750-950 |
| 3.3L & 3.9L | 700-950 |
MINIMUM AIRFLOW IDLE SPEED
THROTTLE POSITION SENSOR
Note. Throttle Position Sensor (TPS) is not adjustable. The following procedures may be used to check TPS calibration.
- Turn ignition switch to "ON" position. DO NOT start engine. Measure voltage at center terminal of TPS, with throttle valve fully closed against stop. Voltage should be 1.5 volts or less. If voltage is not 1.5 volts or less, replace TPS.
- Slowly open throttle valve to wide open throttle. TPS voltage should gradually increase to at least 3.4 volts. If voltage does not gradually increase to at least 3.4 volts, replace TPS.