Owner's Problem Description
The owner reports that their 1996 Plymouth Voyager with a 3.3L engine was initially running fine but began stalling and then died completely. The vehicle now cranks but won't fire. The owner has replaced several components, including spark plugs, wires, crankshaft and camshaft sensors, ignition coil pack, and fuel filter. After replacing the PCM, the van now won't crank at all, and the owner seeks assistance.
Professional Technical Analysis
This 1996 Plymouth Voyager is equipped with a 3.3L V6 engine and has likely accumulated over 150,000 miles. The owner describes a sequence of stalling events leading to a complete shutdown. Initially, the vehicle cranked but failed to start, indicating potential ignition or fuel delivery issues. The owner has replaced critical components including the spark plugs, ignition wires, crankshaft position sensor, camshaft position sensor, ignition coil pack, and fuel filter without resolving the issue. After replacing the PCM, the vehicle now does not crank, which suggests a potential issue with either the new PCM or related wiring/connectors. The PCM replacement is crucial as it controls the ignition and fuel systems; if improperly installed or incompatible, it can prevent cranking. Additionally, the absence of spark at the plugs points to possible ignition system failures, while the lack of crank after PCM replacement raises concerns about battery connections, starter relay, or security system activation, especially if the vehicle has an anti-theft feature. Checking for any stored trouble codes using an OBD-II scanner will help narrow down the diagnostic approach, focusing on both the electrical integrity and the components involved in the ignition and fuel delivery systems.
Possible Causes
Most common causes (ordered by frequency):
- Ignition System Failure: The lack of spark at the plugs indicates a potential failure in the ignition system, which may include the ignition coil or faults in the wiring harness connecting the PCM to the ignition components. The coil pack may not be delivering sufficient voltage, or connections may be corroded or loose. Testing the coil pack's resistance should show between 0.5-1.5 ohms for primary windings and 6.5-12 kOhms for secondary windings. - No spark at plugs, failed ignition coil tests, possible stored ignition system fault codes.
- PCM Compatibility Issue: The replacement PCM from the wrecking yard may not be compatible with the vehicle's existing systems, leading to non-functionality in cranking or ignition. It's essential to verify that the replacement PCM matches the vehicle's VIN and part number specifications. If the PCM is incorrect, it may inhibit cranking or fail to communicate with the ignition or fuel systems properly. - PCM part number mismatch, no communication with OBD-II scanner, vehicle-specific specifications not met.
- Starter Motor or Relay Failure: The vehicle not cranking after PCM replacement could indicate a failure in the starter motor or its relay. A faulty starter relay may not send the signal to engage the starter. Testing the starter relay should show continuity when activated, and the starter motor should draw between 10-30 amps when engaged. - No engagement of starter motor, relay testing shows no continuity, battery voltage at 12.6V.
- Electrical Connection Issues: The symptoms described may also be due to poor electrical connections, particularly at the battery terminals, PCM connectors, or ground points. Loose or corroded connections can lead to insufficient voltage reaching critical components. All battery connections should be cleaned and tightened, and ground connections should be verified for integrity. - Corroded battery terminals, loose PCM connections, intermittent electrical faults observed.
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 OBD-II Diagnostic Scan: Use an OBD-II scanner or GeekOBD APP to check for any stored trouble codes. This will provide insight into the current issues affecting the vehicle, particularly focusing on ignition and fuel system codes. Look for any active or pending codes that may indicate faults in ignition timing or fuel delivery.
- STEP 2 - Spark and Fuel Pressure Testing: With a helper, check for spark at the ignition plugs while cranking the engine. If there is no spark, proceed to test the ignition coil. Also, check the fuel pressure at the fuel rail to ensure it is within specification, ideally between 35-45 PSI. Fuel pressure testing will help identify if there are issues with the fuel pump or filter.
- STEP 3 - Verify PCM Installation and Compatibility: Confirm that the PCM is correctly installed and matches the original unit's specifications. Check wiring harness connections for corrosion or damage. Use the voltmeter to check for proper voltage at the PCM connectors and ensure that all grounds are secure.
- STEP 4 - Check Starter Motor and Relay Function: Test the starter motor and its relay by applying direct power to the starter. If the starter engages, the relay may be faulty. If it does not engage, the starter motor may need to be replaced. Ensure that the battery voltage is adequate and connections are secure.
