Owner's Problem Description
The owner reports that the 2000 Dodge Stratus has a rough idle, feeling as if it skips. The issue smooths out between 10-45 mph but starts hitching between 50-55 mph. Additionally, there is a noticeable rotten egg smell from the exhaust. The owner has replaced some components but still experiences the symptoms, indicating a deeper issue.
Professional Technical Analysis
This 2000 Dodge Stratus with approximately 150,000 miles is exhibiting rough idle and performance issues, including a distinct rotten egg smell from the exhaust. The symptoms manifest as a rough idle, which is particularly noticeable when the vehicle is stationary or moving slowly. At moderate speeds (10-45 mph), the performance smooths out, but noticeable hitching occurs at higher speeds (50-55 mph). These symptoms suggest potential issues with the fuel system, ignition system, or catalytic converter. The presence of a rotten egg smell indicates that sulfur compounds are being produced, likely due to a rich fuel mixture or a failing catalytic converter. The owner has already ruled out several common culprits including the catalytic converter, coil pack, MAF sensor, oxygen sensor, spark plugs, and wires. The check engine light is illuminated, with a notable code pointing to the MAF sensor not holding pressure, which could indicate an air intake issue or fuel mixture imbalance. This vehicle's rough idle could stem from incorrect fuel delivery or excessive fuel entering the exhaust system, leading to catalytic converter saturation. Analyzing the fuel pressure and inspecting the fuel injectors for proper operation will be critical. Additionally, checking the MAF readings under load will clarify if the sensor is providing accurate data to the PCM.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Injector Malfunction: Clogged or malfunctioning fuel injectors can lead to improper fuel delivery, resulting in a rich mixture. This can cause rough idling and poor acceleration, which may explain the hitching at higher speeds. Testing injector operation and flow rate is essential; they should deliver a consistent spray pattern with sufficient pressure (typically 40-50 PSI). - Rough idle, check engine light, potential fuel delivery issues based on performance symptoms.
- Mass Air Flow (MAF) Sensor Failure: The MAF sensor may be providing incorrect readings to the PCM, causing an improper air-fuel mixture. This could lead to poor combustion and the rotten egg smell from unburned fuel in the exhaust. Testing the MAF sensor for proper voltage output (should be around 0.5-4.5V) while monitoring engine load could reveal faults. - Check engine light with MAF sensor related trouble codes, rough idle, and performance issues.
- Catalytic Converter Failure: A failing catalytic converter can cause back pressure, resulting in poor engine performance and a rotten egg smell. If the converter is clogged, it can restrict exhaust flow, leading to rough idling and hitching at speed. A pressure test before and after the converter can determine if it's functioning correctly. - Presence of rotten egg smell, potential performance loss, and symptoms of back pressure.
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 and Code Retrieval: Utilize a professional OBD-II scanner or the GeekOBD APP to retrieve any stored codes, particularly focusing on MAF sensor-related codes. Analyze freeze frame data to understand conditions under which the codes were set. This step is crucial for identifying miscommunication between MAF sensor readings and engine performance.
- STEP 2 - Live Data Monitoring: Use the GeekOBD APP to monitor live data from the MAF sensor, checking for voltage output during idle and under load. Ensure that the MAF voltage is within the expected range (0.5-4.5V). Additionally, monitor fuel trim values to see if the engine is running rich, which can indicate a problem with the fuel system or MAF sensor.
- STEP 3 - Fuel Pressure Test: Connect a fuel pressure gauge to the fuel rail and verify pressure readings. The pressure should be within the specified range (40-50 PSI) during idle and while revving the engine. A low reading may indicate a failing fuel pump or clogged filter, both of which can contribute to poor engine performance.
- STEP 4 - Catalytic Converter Assessment: If previous steps do not reveal the issue, conduct a pressure test on the catalytic converter. Measure the exhaust pressure before and after the converter to diagnose any restrictions. If the pressure drop is significant, it indicates a clogging issue that needs to be addressed.
