Owner's Problem Description
A 1999 Plymouth Voyager suddenly died while accelerating from a stop. The owner noted that the engine has good power and cranks without issue but shows no spark when the coil wire is tested. Previous rough idle issues led to a code for the EGR valve, but now no codes can be retrieved with the OBD-II scanner, and the check engine light is off. The owner is seeking a second opinion on the potential for a faulty computer after previous suggestions.
Professional Technical Analysis
The 1999 Plymouth Voyager is equipped with a 3.3L V6 engine and has approximately 150,000 miles on the odometer. The primary symptom is a complete lack of spark during cranking, which can be indicative of several issues in the ignition system. Given the reported history of rough idle and a previous EGR valve code, there may be a connection between the two. The vehicle appears to crank normally, and the fuel pump operates as expected, building pressure and shutting off appropriately. However, the distributor is noted to be non-functional, indicating that the timing belt has likely failed, as the rotor is not turning. This points to a potential timing belt failure, which in non-interference engines like this one, generally does not cause valve damage but will prevent ignition. When diagnosing, it is crucial to check the integrity of the ignition coil and associated wiring, as well as the crankshaft position sensor, which is critical for spark generation. A thorough inspection of the ignition control module (ICM) and the power distribution center should also be conducted to ensure there are no additional electrical faults. Given the age and mileage of the vehicle, it's not uncommon for timing belts to fail, necessitating a replacement along with the water pump as a preventive measure during the repair process.
Possible Causes
Most common causes (ordered by frequency):
- Timing Belt Failure: The timing belt in the 3.3L V6 engine may have broken, which prevents the distributor from turning and consequently the ignition system from firing. This is common in vehicles with high mileage, and the absence of crankshaft rotation under the distributor cap confirms this diagnosis. Normal service intervals for timing belt replacement are typically around 60,000 to 100,000 miles. - Distributor rotor not turning during cranking, confirmed timing belt breakage, engine is non-interference design.
- Ignition Control Module (ICM) Failure: The ICM may have failed, which can prevent the ignition coil from receiving the necessary signals to produce a spark. Since the coil tested fine at the parts store, it's essential to check the ICM and its connections for any signs of failure. - No spark at the coil, ICM failure could explain loss of ignition signal, possible previous rough idle linked to ICM issues.
- Crankshaft Position Sensor Failure: A faulty crankshaft position sensor can prevent the engine from starting by not providing the signal needed for the ignition system to function. Testing the sensor's resistance and signal output while cranking can help confirm this issue. - Lack of spark, potential stored codes may indicate sensor failure, resistance should typically be within 200-500 ohm range.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Inspection: Begin by visually inspecting the engine bay for any obvious signs of damage or disconnections, especially around the timing belt area. Check the integrity of the timing belt cover for any signs of wear or damage. Ensure that all electrical connections to the ignition system components are secure.
- STEP 2 - Verify Crankshaft Rotation: With the ignition key in the 'start' position, observe the distributor cap to see if the rotor turns. If it does not, this strongly indicates a timing belt failure. If the rotor is turning, proceed to check for spark at the ignition coil.
- STEP 3 - Test Ignition Components: If the rotor is turning, use a multimeter to measure voltage at the ignition coil's positive terminal. It should read approximately 12V when cranking. Proceed to check the ICM for proper operation and inspect for any fault codes using an OBD-II scanner.
- STEP 4 - Inspect Crankshaft Position Sensor: If spark is still absent, test the crankshaft position sensor for proper resistance and signal output. This sensor is critical for ignition timing and should show a resistance within the specified range. If faulty, replace the sensor and retest for spark.
