Owner's Problem Description
The vehicle starts and revs normally, but the engine dies when put into gear and torque is applied while driving. The owner has replaced several components including the PCM, crank sensor, cam sensor, plugs, wires, cap, rotor, and coil. After shutting off the key, the engine can be restarted, but the issue recurs more quickly with repeated attempts. No trouble codes are present, but it appears that the crank sensor loses signal, shutting off the ASD relay.
Professional Technical Analysis
This 1995 Dodge Truck equipped with a 5.2L V8 engine, likely with over 150,000 miles, is exhibiting symptoms of stalling under load, particularly when shifting into gear and accelerating. The absence of diagnostic trouble codes (DTCs) complicates the diagnosis, suggesting an intermittent electrical issue rather than a mechanical failure. The crankshaft position sensor (CPS) is critical for the operation of the powertrain control module (PCM) and when it fails to provide a signal, the Automatic Shutdown (ASD) relay is deactivated, cutting power to essential components. This situation leads to engine stalling. The PCM replacement and other component changes indicate a troubleshooting effort aimed at correcting potential failure points. However, it is essential to test for spark and fuel delivery when the engine dies, as these factors determine if the issue is related to ignition or fuel systems. A systematic approach using the GeekOBD APP for monitoring live data during operation is recommended to capture any anomalies in sensor readings, especially the crankshaft position sensor voltage. The CPS should show a consistent signal of approximately 0.5V to 5V depending on crankshaft position. When the engine dies, a drop in this voltage or a complete loss of signal could indicate the root cause. Additionally, examining wiring harness integrity and electrical connections for corrosion or damage is crucial. The current condition of the vehicle suggests immediate attention to potential electrical failures, which could pose safety risks if the engine stalls unexpectedly in traffic.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor Failure: The CPS may intermittently lose signal due to internal failure or wiring issues, causing the PCM to lose reference for ignition timing and fuel delivery. Voltage readings at the CPS connector should be checked; a stable signal between 0.5V and 5V is expected. If the signal drops to 0V when the engine stalls, it indicates a likely CPS failure. - Engine dies under load, inability to restart immediately, signal loss at CPS connector during stall.
- Wiring Harness Issues: Damaged or corroded wiring in the CPS circuit could interrupt the signal to the PCM. Visual inspection and continuity testing should be performed to ensure that all connections are secure and free from corrosion. Look for signs of wear, especially near connectors and in areas prone to heat or vibration. - Visual inspection shows frayed wires, intermittent loss of signal during testing.
- ASD Relay Malfunction: The Automatic Shutdown relay might be faulty, causing it to drop power unexpectedly, leading to engine stalling. Testing the relay for continuity and operation under load is essential. The relay should click on activation and maintain power supply during operation. - Intermittent power loss to PCM, relay does not click or holds under load.
- Fuel Delivery Issues: Although ignition components have been replaced, fuel delivery may still be inadequate. The fuel pump pressure should be tested to ensure it meets specifications (40-50 PSI for this engine). If pressure is low, consider checking the fuel filter and pump operation. - Low fuel pressure during testing, hesitation in acceleration.
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 - OBD-II Scan: Start with a thorough OBD-II scan using the GeekOBD APP to check for any stored codes or pending codes. Pay particular attention to freeze frame data, which can provide insight into the vehicle's condition at the time of the fault. Even in the absence of codes, this data can help narrow down potential issues.
- STEP 2 - Live Data Monitoring: Utilize the GeekOBD APP to monitor live data while driving the vehicle. Focus on the crankshaft position sensor's output voltage, which should range from 0.5V to 5V. Document any fluctuations or drops in voltage when the engine stalls. This will help identify if the CPS is failing under load.
- STEP 3 - Physical Inspection: Conduct a thorough visual inspection of the wiring harness and connectors associated with the CPS and ASD relay. Look for frayed wires, corroded connectors, and any signs of wear. Perform continuity tests with a multimeter to ensure there are no breaks in the circuit.
- STEP 4 - Relay and Component Testing: Test the ASD relay for functionality. Ensure that it clicks when activated and remains operational under load. If necessary, replace with an OEM part (e.g., P/N 56028500AA). Also, check fuel pressure at the fuel rail to confirm it meets the required specifications.
