Owner's Problem Description
The owner of a 2007 Saturn Ion 2 reports that the emissions light remains on and a misfire has been detected in cylinder 3. The vehicle is consuming twice the normal amount of gas, with the emissions light occasionally flashing and then turning off. Previous repairs included replacing the spark plug and coil for cylinder 3, as well as the upstream oxygen sensor, but these actions have not resolved the issues. The owner is seeking further diagnostic advice.
Professional Technical Analysis
This 2007 Saturn Ion 2, equipped with a 2.2L inline-4 engine and approximately 120,000 miles, presents with an illuminated emissions light and a misfire code specifically for cylinder 3. The vehicle exhibits excessive fuel consumption, consuming roughly double the expected mileage, indicating a potential fuel metering issue or incomplete combustion. The intermittent nature of the emissions light, which occasionally flashes, suggests misfire events that could be severe enough to trigger the onboard diagnostics (OBD-II) system to flag a fault. Past repairs, including the replacement of the spark plug and ignition coil for cylinder 3, along with the upstream oxygen sensor, have not rectified the underlying issue, hinting at potential deeper mechanical or electrical faults. It’s crucial to assess the engine’s health through a compression test to rule out internal engine problems such as worn piston rings or valves, which could lead to a misfire. Factors such as environmental conditions (temperature, fuel quality) and maintenance history (previous repairs, mileage-related wear) also play a pivotal role in the diagnostic process. Also, checking for vacuum leaks or issues with the fuel delivery system (fuel injectors) should be prioritized. Given these factors, further investigation is necessary to identify the root cause and ensure the vehicle operates reliably and efficiently.
Possible Causes
Most common causes (ordered by frequency):
- Low Compression in Cylinder 3: A compression test may reveal low cylinder pressure due to worn piston rings or valve issues, which can cause misfires and increased fuel consumption. Normal compression for this engine should be within 150-180 psi. If compression is below 100 psi, it indicates serious internal engine problems. - Compression test results showing low psi in cylinder 3.
- Fuel Injector Malfunction: A failing fuel injector in cylinder 3 may not deliver the correct amount of fuel, leading to a rich condition and misfire. Fuel injectors should operate within specified resistance ranges (12-16 ohms) and should be tested for proper spray pattern. - Poor fuel spray pattern observed during injector testing.
- Vacuum Leak: A vacuum leak can cause lean conditions, leading to misfires and poor fuel economy. Inspecting vacuum hoses and intake manifold gaskets is critical, as any leak could affect the air-fuel mixture. - Hissing sound during idle and visual inspection of vacuum hoses shows wear.
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 - Compression Test: Perform a compression test on all cylinders to assess the health of the engine. Use a compression tester, and ensure readings are within 150-180 psi for healthy cylinders. If the reading in cylinder 3 is significantly lower, it could indicate internal engine issues such as worn piston rings or valves.
- STEP 2 - Fuel Injector Testing: Check the resistance of the fuel injector for cylinder 3. It should measure between 12-16 ohms. If it’s outside this range, consider replacing the injector. Also, perform a flow test to check the spray pattern and quantity of fuel delivered.
- STEP 3 - Inspect Vacuum Lines: Visually inspect all vacuum lines and the intake manifold for any signs of leaks. Use a smoke machine if available to detect hard-to-find leaks. Ensure all connections are tight and gaskets are intact.
