Owner's Problem Description
The owner reports that the engine light is always on, with a P0302 code indicating a cylinder 2 misfire. The engine light sometimes blinks while idling. Additionally, the Service Stabilitrack and Service Traction Control lights frequently illuminate. Recent repairs include new spark plugs, a coil, and a mass airflow sensor, but the issue persists. Occasionally, a rich gasoline smell is noted.
Professional Technical Analysis
This 2009 Saturn Vue, equipped with a 3.6L V6 engine and AWD, has approximately 120,000 miles. The persistent engine light indicates a P0302 code, which signifies a misfire in cylinder 2. The blinking light at idle suggests that the misfire is intermittent. With recent repairs including new spark plugs, a coil, and a mass airflow sensor, the symptoms have not improved, indicating a deeper underlying issue. The frequent illumination of the Service Stabilitrack and Traction Control lights suggests potential problems with the vehicle's stability control systems, possibly linked to the misfire issue. The reported low compression of 85 psi in cylinder 2, compared to 150 psi in adjacent cylinders, indicates significant internal engine issues such as a blown head gasket, worn piston rings, or valve problems that need urgent attention. Additionally, the rich gasoline smell may point to fuel system problems or improper air-fuel mixture due to the misfire. Safety concerns arise from the vehicle’s compromised performance and potential for stalling, particularly under load. The combination of codes and symptoms warrants a thorough diagnostic approach focusing on compression testing, ignition system verification, and fuel injector performance assessment.
Possible Causes
Most common causes (ordered by frequency):
- Low Compression in Cylinder 2: The reported 85 psi compression in cylinder 2 is significantly below the normal range of 150 psi found in other cylinders. This low compression can be due to several issues, including worn piston rings, a blown head gasket, or damaged valves. These conditions prevent proper combustion, leading to misfires and contributing to the persistent engine light. It is critical to perform a compression test to confirm these findings and assess the overall engine health. - Compression test results, misfire symptoms, and performance issues during operation indicate significant engine wear.
- Fuel Injector Issues: If the fuel injector for cylinder 2 is malfunctioning or clogged, it may not be delivering the appropriate amount of fuel, causing a rich fuel condition and leading to misfiring. Testing the injector's pulse and flow rate is essential to determine if it is functioning correctly. If the injector is not receiving the proper pulse from the PCM, this could also lead to misfire codes. - Rich fuel smell, potential fuel system codes, and injector functionality tests indicating issues.
- Ignition Coil Malfunction: Despite a recent coil replacement, if the new coil is faulty or if there are issues with the ignition control module, it could result in intermittent spark delivery to the cylinder. This could explain the misfire in cylinder 2 and should be verified by swapping the coil with another cylinder to see if the misfire moves. - Intermittent misfire patterns, recent coil replacement, and need for further ignition component testing.
- Vacuum Leaks: Any vacuum leak in the intake manifold can lead to an improper air-fuel mixture, causing a rich condition and misfires. Inspecting all vacuum lines and the intake system for leaks can help identify if this is contributing to the misfire in cylinder 2. - Symptoms of rough idling, hissing sounds during acceleration, and visual inspections for leaks.
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 with a thorough OBD-II scan using GeekOBD APP to retrieve any stored codes and freeze frame data. Pay special attention to the P0302 misfire code and any other pending codes that might provide additional insight into the issue. Review the vehicle's history for previous repairs related to the ignition and fuel systems.
- STEP 2 - Compression Testing: Perform a compression test on all cylinders, focusing on cylinder 2. A compression reading below 150 psi indicates potential issues that require further investigation. Document results for each cylinder and compare them to factory specifications to assess engine health.
- STEP 3 - Fuel Injector Testing: Use a fuel pressure gauge to test the fuel system pressure, which should be within the range of 50-60 psi. Additionally, perform an injector pulse test to ensure the injector is receiving the proper signal and is functioning correctly. If the injector does not perform as expected, further inspection or replacement may be necessary.
- STEP 4 - Ignition System Verification: Verify the operation of the ignition coil and associated components. Swap the ignition coil from cylinder 2 with another cylinder to see if the misfire code moves. Check the ignition control module for proper operation and response. Look for any signs of arcing or damage in the ignition system.
- STEP 5 - Visual Inspection for Vacuum Leaks: Conduct a thorough visual inspection of the intake system and vacuum lines for any signs of leaks. Use a smoke machine if available to identify any hidden leaks. Address any leaks found as they can significantly affect engine performance and contribute to misfires.
