Owner's Problem Description
The owner reports a rotten egg smell from the exhaust when the air conditioner is on, especially noticeable after turning off the vehicle, and occasionally at red lights. The check engine light is not illuminated, and there’s no noticeable decrease in fuel mileage. The vehicle experiences a shaking sensation when first accelerating, lasting about two seconds before shifting into second gear, after which it operates normally.
Professional Technical Analysis
The 2005 Mitsubishi Endeavor, equipped with a 3.8L V6 engine, experiences a distinct rotten egg smell emanating from the exhaust system, particularly when the air conditioning is activated. This phenomenon is typically indicative of a catalytic converter issue, often associated with rich fuel conditions that allow unburned fuel to reach the converter, producing hydrogen sulfide (the source of the rotten egg smell). Given that the check engine light is not illuminated, this could suggest that the issue has not yet triggered a fault code within the engine control module (ECM). However, it’s essential to investigate if the engine is, in fact, running rich, potentially due to a malfunctioning sensor (such as the oxygen sensor), fuel injector issues, or even an air intake leak. The intermittent shaking felt during acceleration—lasting about two seconds—suggests possible misfiring or a disruption in the ignition system. This could stem from worn spark plugs, faulty ignition coils, or issues with fuel delivery. It is also noteworthy that the shaking does not occur during gear shifts but rather at initial acceleration, indicating it may not be directly related to the transmission itself, although a torque converter issue should not be ruled out. The vehicle’s current condition warrants a thorough diagnostic approach to confirm the root causes of both the exhaust smell and the shaking during acceleration.
Possible Causes
Most common causes (ordered by frequency):
- Catalytic Converter Malfunction: The rotten egg smell is often due to a failing catalytic converter, which may not be properly processing exhaust gases. This could be caused by rich running conditions, leading to hydrogen sulfide emissions. The catalyst's efficiency can degrade over time, especially if the vehicle has not had regular maintenance or has experienced issues like misfires that send unburned fuel into the exhaust. Testing the converter's efficiency through back pressure tests or temperature differentials can confirm its condition. - Presence of rotten egg smell from exhaust, symptoms worsen with A/C operation, potential misfire indications.
- Oxygen Sensor Failure: A faulty oxygen sensor can provide incorrect readings to the ECM, leading to an overly rich fuel mixture. This can contribute to the rotten egg smell as unburned fuel passes through the catalytic converter. Testing the sensor for voltage output (0.1V to 0.9V under normal operating conditions) and ensuring it switches appropriately during operation will help verify its functionality. - Potential for rich fuel mixture indicated by exhaust smell, lack of check engine light suggests non-critical faults, and irregular fuel trims.
- Ignition System Issues: Misfiring due to faulty spark plugs or ignition coils could lead to incomplete combustion, causing both the shaking during acceleration and the exhaust odor. Each cylinder should be tested for spark quality, and coils should be checked for resistance (typically 0.5 to 1.5 ohms). A weak spark can lead to rich conditions in the exhaust system. - Shaking during initial acceleration, potential misfire codes in the system, and signs of wear on ignition components.
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: Begin with a full OBD-II scan using a professional scan tool or the GeekOBD APP to check for any stored or pending codes. Since the check engine light is not illuminated, it’s essential to examine freeze frame data for any parameters that may indicate the engine is running rich or if there are any recorded misfires.
- STEP 2 - Live Data Monitoring: Use the GeekOBD APP to monitor live data, focusing on fuel trims, oxygen sensor output, and engine load. Assess fuel trims to confirm if they are consistently outside the normal range (-10% to +10%). An excessively rich fuel trim can indicate an underlying issue with either the oxygen sensor or fuel delivery system.
- STEP 3 - Component Testing: Inspect ignition components for wear, including spark plugs and ignition coils. Measure the resistance of the ignition coils to ensure they fall within the standard range (0.5-1.5 ohms). Perform a spark test to ensure all cylinders are receiving adequate spark. Additionally, inspect the catalytic converter for signs of blockage or overheating.
- STEP 4 - Road Test and Observation: Conduct a controlled road test while monitoring real-time data with the GeekOBD APP. Pay attention to any fluctuations in RPM during initial acceleration and observe if the rotten egg smell persists under different driving conditions, especially with the A/C on.
