Owner's Problem Description
The owner of a 2008 Dodge Magnum reports that after changing the third ignition coil and all spark plugs, the check engine light remains on. The car initially runs, but after some time, it cuts off and the engine light starts flashing, indicating a potential misfire. The firing order was confirmed to be 5-6-3-4-1-2, with cylinders 1 and 2 located at the front of the engine.
Professional Technical Analysis
The 2008 Dodge Magnum is equipped with a 5.7L HEMI V8 engine, typically exhibiting approximately 120,000 miles. The reported symptoms include an intermittent misfire, especially noticeable after the engine has warmed up. The check engine light flashing indicates a potentially severe misfire situation. The firing order for this engine is 1-8-4-3-6-5-7-2, which is important for diagnosing and rectifying any issues related to ignition timing and cylinder firing sequence. Given that the owner replaced the third ignition coil, it's crucial to check the integrity of the ignition system components including the coil-on-plug (COP) assemblies and the associated wiring for any signs of wear or damage. Additionally, the PCM (Powertrain Control Module) plays a vital role in monitoring cylinder misfires, which could lead to misdiagnosis if not checked properly. Previous repair history indicates potential wiring issues or improper installation, which could also contribute to ongoing problems. A comprehensive diagnostic scan should be performed to retrieve any stored trouble codes that can provide insight into which cylinder is misfiring. Based on the symptoms described, it is recommended to check for fault codes (likely P0300 for random misfire, or specific codes like P0301-P0308 for individual cylinders) and evaluate the live data for RPM fluctuations during misfire events. The vehicle’s current condition suggests immediate attention is needed to avoid further engine damage and ensure reliable operation.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Ignition Coil: Even after replacing the third ignition coil, the remaining coils may have degraded due to heat stress or excessive mileage, leading to inconsistent spark delivery. Each coil should be tested for resistance within the 0.5-1.5 ohm range. Additionally, it is essential to inspect for any arcing or carbon tracking on the coil boot. - Check engine light, misfire codes P0301 to P0308, visual inspection of ignition coils shows potential wear.
- Wiring Issues: Damaged or corroded wiring harness connections to the ignition coils can cause erratic spark delivery, leading to misfires. The wiring should be inspected for continuity and proper resistance, ideally below 5 ohms for reliable operation. - Fluctuating resistance readings during tests, visible corrosion on connectors, intermittent spark at ignition coils.
- Fuel Delivery Issues: Insufficient fuel pressure or delivery can lead to misfires. The fuel system pressure should be checked with a gauge, which should maintain 58-62 PSI. If the pressure is low, inspect the fuel pump and filter for blockages or failures. - Low fuel pressure reading on gauge, potential fuel pump noise, lean condition observed in fuel trims.
- PCM Software Issues: The Powertrain Control Module may require a software update to correctly manage ignition timing and misfire detection. Checking for Technical Service Bulletins related to PCM updates can be beneficial. - Previous TSBs indicate similar issues; performing a software update may resolve the misfire.
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 Scanning: Begin by using an OBD-II scanner or GeekOBD APP to retrieve any diagnostic trouble codes (DTCs). This will help identify any specific cylinders that are misfiring and provide insight into the underlying issues. Pay attention to any freeze frame data that may indicate conditions during the misfire events.
- STEP 2 - Live Data Monitoring: Utilize the GeekOBD APP to monitor live data, focusing on RPM fluctuations, fuel trims, and ignition timing. This can help pinpoint the exact moment the misfire occurs and correlate it with other engine parameters. Ensure that fuel pressure is within the normal range (58-62 PSI) during idle and under load conditions.
- STEP 3 - Visual and Physical Inspection: Perform a thorough visual inspection of the ignition system, including the ignition coils and wiring harness. Physically check for any signs of wear, corrosion, or damage. Test the ignition coils for proper resistance and inspect the wiring for continuity and proper voltage supply.
- STEP 4 - Fuel Pressure Testing: Connect a fuel pressure gauge to the fuel rail to measure the fuel pressure. Ensure it maintains 58-62 PSI during key-on engine-off (KOEO) and during engine operation. If pressure is low, investigate the fuel pump and filter for blockages or failures.
