Owner's Problem Description
The owner reports that their 2007 Dodge Charger with a 2.7L V6 engine developed an extremely rough idle after warming up. Initially, the engine idles smoothly when cold, but as it warms up, the entire car shakes at idle. The owner previously replaced the spark plugs, suspecting they were the issue, but the problem persists. The check engine light is on, indicating a potential fault in the engine's operation.
Professional Technical Analysis
In this case involving a 2007 Dodge Charger with a 2.7L V6 engine, approximately 100,000 miles, the owner describes an extremely rough idle condition that occurs only after warm-up. This symptom typically suggests a misfire condition, which can be linked to several potential causes. The check engine light has illuminated, which indicates stored fault codes. The retrieved code P0202 indicates an issue with the injector circuit for cylinder 2, which implies that the fuel injector may not be functioning correctly. The analysis should begin with an examination of the injector wiring harness for any breaks or grounding issues. Since the injector shows proper voltage but does not affect idle when unplugged, it suggests that the injector may be failing or the cylinder itself may have issues such as low compression or a faulty spark plug. Given that the spark plugs were recently replaced, attention should also be directed toward the ignition coils, especially since one of the coil boots appeared burnt. This could indicate arcing or a failure in the ignition coil, thus impacting cylinder operation. The rough idle and check engine light are significant safety concerns that necessitate immediate attention to avoid further damage to the engine and ensure reliability.
Possible Causes
Most common causes (ordered by frequency):
- Injector Circuit Issue: The P0202 code indicates an open circuit in the injector circuit for cylinder 2. This could be due to damaged wiring or a faulty injector. The injector should be ohmed to confirm resistance (typically 12-16 ohms for most fuel injectors). If the wiring is intact and the injector resistance is within specification, further investigation into the PCM or wiring harness may be required. - Check engine light on, P0202 code stored, no change in idle when injector is unplugged.
- Ignition Coil Failure: The burnt appearance of the coil boot suggests that the ignition coil may be arcing or failing. A faulty ignition coil can lead to a misfire in the corresponding cylinder, causing rough idle. Testing the ignition coil's primary and secondary resistance (typically 0.4-2.0 ohms for primary and 6,000-15,000 ohms for secondary) will confirm its operational status. - Burnt coil boot, potential arcing, rough idle corresponding with cylinder 2.
- Wiring Harness Damage: Inspect the wiring harness leading to the injector for any signs of wear, chafing, or corrosion. A damaged harness can lead to intermittent connectivity, affecting injector performance and idle stability. Visual inspection followed by continuity testing is essential. - Visual inspection of wiring for breaks or damage, continuity test results.
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 - Retrieve Diagnostic Codes: Use a professional OBD-II scanner or GeekOBD APP to retrieve any stored codes. Pay particular attention to P0202 and any additional codes that may indicate related issues. Analyze freeze frame data to understand the conditions under which the faults occurred.
- STEP 2 - Inspect Fuel Injector Circuit: Visually inspect the wiring harness and connector leading to the cylinder 2 injector for any signs of damage or corrosion. Perform an ohm test on the injector (should read 12-16 ohms). Check for 12V power at the connector with the key in the ON position.
- STEP 3 - Test Ignition Coil: Remove the ignition coil for cylinder 2 and test its primary and secondary resistance. Ensure primary is between 0.4-2.0 ohms and secondary is between 6,000-15,000 ohms. Inspect the coil boot for arcing or damage.
- STEP 4 - Conduct a Road Test: After addressing any found issues, conduct a road test while monitoring live data using the GeekOBD APP. Pay attention to any misfires, fuel trims, and engine performance under different load conditions to confirm repair effectiveness.
