Owner's Problem Description
The owner of a 1998 Dodge Intrepid reports that the vehicle experiences stalling issues, particularly after an engine swap from a 2.7L to a 3.2L engine done a couple of years ago. The original computer from the 2.7L engine is still in use. Symptoms occur intermittently while driving, and the engine may not restart until it cools down. No previous repairs were mentioned aside from the engine swap. The current condition of the vehicle is unstable with concerns about safety while driving.
Professional Technical Analysis
The 1998 Dodge Intrepid equipped with a 3.2L engine (approximately 120,000 miles) is experiencing intermittent stalling, particularly after the engine swap from a 2.7L engine. This issue arises when the engine is under load, and the check engine light may illuminate intermittently. Given the engine swap, it's essential to analyze the compatibility of the engine control unit (ECU) with the new engine. The original ECU from the 2.7L engine may not be properly calibrated for the 3.2L engine's parameters, leading to improper fuel mapping and potential ignition timing issues. Furthermore, the crankshaft and camshaft position sensors are critical for engine timing and can often fail or provide erratic signals, resulting in stalling. Testing these sensors is essential, as they should have resistances typically ranging from 500-1,500 ohms when cold. Additionally, the engine coolant temperature (ECT) sensor can contribute to stalling if it is malfunctioning, as it influences fuel delivery based on engine temperature. The ECT sensor should show a resistance of 2,000-3,000 ohms at 20°C, decreasing as the temperature rises. Current vehicle conditions indicate possible overheating of the sensors leading to failure when hot. Observing fuel pressure, which should be maintained at 35-45 PSI during operation, is also crucial as fuel delivery issues can lead to engine stalling. Finally, verifying spark presence at the ignition coil and checking for proper voltage output is necessary for ensuring the ignition system is functioning correctly.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor Failure: The crankshaft position sensor may fail due to heat exposure or wear, leading to intermittent engine stalling. This sensor typically operates within a resistance range of 500-1,500 ohms when cold. If the sensor fails, the engine may not receive timing signals, resulting in stalling. It should be tested for continuity and resistance when the engine is cool. A common symptom of failure is erratic ignition timing and associated fault codes such as P0335. - Intermittent stalling, check engine light activation, stored codes P0335
- Camshaft Position Sensor Malfunction: Similar to the crankshaft sensor, the camshaft position sensor can fail due to exposure to heat or aging. It provides critical timing information to the ECU for fuel injection and spark timing. The expected resistance value should also be in the range of 500-1,500 ohms. A malfunction may cause the engine to stall unexpectedly, particularly at idle or under load. - Unexpected stalling, poor engine performance under load, potential stored codes P0340
- Engine Coolant Temperature (ECT) Sensor Issues: The ECT sensor can degrade over time, leading to incorrect temperature readings. This can result in improper fuel mixture and engine stalling, particularly when the engine is hot. Resistance should measure approximately 2,000-3,000 ohms at 20°C. If the sensor is faulty, it may cause the engine not to restart until it cools down, as the ECU is misled about the engine's actual temperature. - Stalling after reaching operating temperature, delayed restart until cooling, possible stored codes P0117
- Fuel Pressure Issues: Insufficient fuel pressure can lead to engine stalling. The fuel pump should maintain a pressure of 35-45 PSI. A drop below this range can cause the engine to stall under load. Testing fuel pressure with a gauge at the fuel rail test port is essential to ensure adequate fuel delivery. If the pressure is low, check for fuel pump operation and filter conditions. - Low fuel pressure readings, potential fuel pump failure, engine stalling during 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 - Initial OBD-II Scan: Start by using a professional OBD-II scanner or GeekOBD APP to retrieve any stored trouble codes and freeze frame data. This step will identify potential issues indicated by the ECU and provide insights into the conditions when the stalling occurs. Pay special attention to codes related to the crankshaft and camshaft position sensors, as well as the ECT sensor.
- STEP 2 - Live Data Monitoring: Utilizing the GeekOBD APP, monitor live data to check the performance of critical sensors, including the crankshaft position sensor, camshaft position sensor, and ECT sensor. Look for resistance values and voltage outputs to ensure they are within specified ranges. Pay attention to any fluctuations that correlate with engine stalling symptoms.
- STEP 3 - Component Testing: Test individual components based on previous scan results. Measure the resistance of the crankshaft and camshaft position sensors to ensure they are within 500-1,500 ohms. Additionally, test the ECT sensor resistance at various temperatures to evaluate its functionality. If any sensors are out of specification, they should be replaced.
- STEP 4 - Fuel Pressure Check: Use a fuel pressure gauge to check the pressure at the fuel rail. It should read between 35-45 PSI under normal operating conditions. If the pressure is low, investigate the fuel pump and filter conditions, ensuring that there are no blockages or failures. Additionally, check for proper voltage at the fuel pump while cranking the engine.
