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.
IGNITION TIMING
Note. Always refer to Emission Control Label in engine compartment before attempting service. If manual and label differ, always use emission label specifications.
| CAUTION | DO NOT puncture secondary ignition cables, boots or nipples with test probes. |
Timing is controlled by Powertrain Control Module (PCM) and is not adjustable.
| Application | (1) Degrees BTDC |
|---|---|
| 3.9L | (2) * |
| (1) At idle. (2) Ignition timing is controlled by PCM and is not adjustable. | |
| (1) | At idle. |
| (2) | Ignition timing is controlled by PCM and is not adjustable. |
IGNITION TIMING
IDLE SPEED & MIXTURE
Note. Mixture is controlled by PCM. No adjustment is possible.
Idle speed is controlled by Idle Air Control (IAC) motor. PCM adjusts engine idle speed through IAC motor to compensate for engine load or ambient condition changes. IAC motor is located in throttle body air by-pass passage used to provide air during engine idle. PCM uses inputs from various sensors to determine IAC motor position and change idle speed. Curb idle speed is not adjustable. See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section for diagnosis of incorrect idle speed.
Idle RPM Test
Note. Engine idle speed is not adjustable, however checking idle speed will assist in diagnosing complaints of engine stalling, creeping and hard shifting on vehicles equipped with automatic transmission.
Throttle Body Minimum Airflow
- Set parking brake and block front wheels. Warm engine in Park or Neutral until cooling fan cycles on and off at least once. Ensure all accessories are off. Remove air cleaner assembly and disconnect PCV hose from PCV valve. Attach 0.185" Fixed Orifice Air Metering Fitting (6714) into disconnected vacuum line in place of PCV valve.
- Disconnect idle purge vacuum hose from front of throttle body next to MAP sensor. Cap throttle body vacuum fitting. Connect DRB to DLC. Start engine and allow to idle for at least one minute. Using DRB, access MINIMUM AIRFLOW. When accessed, DRB will count down to stabilize idle RPM and display minimum airflow idle RPM. See «THROTTLE BODY MINIMUM AIRFLOW IDLE SPECIFICATIONS»(/dodge/ram-van-b2500/b-pre-1995-1995/remont/adjustments/#engine-controls-adjustments-39l) table.
- If throttle body minimum airflow idle speed is not within specification, check for vacuum leaks. If there are no vacuum leaks, replace throttle body.
| Application | RPM |
|---|---|
| 3.9L | 500-900 |
THROTTLE BODY MINIMUM AIRFLOW IDLE SPECIFICATIONS
THROTTLE POSITION (TP) SENSOR
Note. TP sensor is not adjustable. Use the following procedures to check TP sensor calibration. For complete testing of TP sensor, see TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
- Remove air cleaner housing assembly. Turn ignition switch to ON position. DO NOT start engine. Using a DVOM, measure voltage at center terminal of TP sensor, with throttle valve in idle position fully closed against stop. Voltage should be within specification. See «THROTTLE POSITION SENSOR VOLTAGE TEST»(/dodge/ram-van-b2500/b-pre-1995-1995/remont/adjustments/#engine-controls-adjustments-39l) table. If voltage is not within specification, replace TP sensor.
- Slowly open throttle valve to Wide Open Throttle (WOT). TP sensor voltage should increase steadily to specification. If voltage does not increase steadily to specification, replace TP sensor.
| Throttle Opening (2) | Volts |
|---|---|
| Idle | Greater Than 0.2 |
| WOT | Less Than 4.8 |
| (1) Voltage should increase steadily as throttle opening is increased from idle position. (2) Measure voltage at throttle position sensor center terminal. | |
| (1) | Voltage should increase steadily as throttle opening is increased from idle position. |
| (2) | Measure voltage at throttle position sensor center terminal. |
THROTTLE POSITION SENSOR VOLTAGE TEST (1)