Experiencing a rough idle or a flashing check engine light in your 2007 BMW 550i can be unsettling. These symptoms often point to engine misfires, a common issue that can stem from various underlying problems. Understanding how to diagnose these misfires using your OBD2 scanner and interpreting the error codes is the first step to getting your BMW back to its optimal performance.
One common scenario involves encountering a series of OBD2 codes after experiencing engine trouble. Consider a situation where a BMW 5-Series, like a 2007 535i (similar engine to the 550i and relevant for diagnostic approaches), initially presented with a range of fault codes, including misfires across multiple cylinders and issues related to fuel injectors and turbo boost. After DME (Digital Motor Electronics) repair, while some initial problems might be addressed, new misfire codes can surface, indicating that the root cause persists or new issues have arisen.
Initially, the fault codes might include:
- 0029CC DME: Combustion misfires, several cylinders
- 0029CF DME: Combustion misfires, cylinder 3
- 0029D1 DME: Combustion misfires, cylinder 5
- 0029F2 DME: Fuel high-pressure system, fuel pressure
These codes collectively suggest a broader issue impacting engine combustion, not isolated to a single cylinder. The “misfires, several cylinders” code (0029CC) is a crucial indicator, highlighting that multiple cylinders are failing to ignite the air-fuel mixture correctly. Codes specifying individual cylinders (0029CF, 0029D1) pinpoint the location of some of these misfires, in this case, cylinders 3 and 5. The fuel pressure code (0029F2) adds another layer, suggesting potential problems with the fuel delivery system, which could be contributing to the misfires.
Following DME repair and clearing the initial codes, a new set of errors emerged shortly after starting the engine, still indicating misfires but with some changes:
- 029CC DME: Combustion misfires, several cylinders (Note the leading ‘0’ is dropped, potentially just a reporting difference but still the same code)
- 0029CF DME: Combustion misfires, cylinder 3
- 0029D1 DME: Combustion misfires, cylinder 5
- 0029F2 DME: Fuel high-pressure system, fuel pressure
- 0030A4 DME: Ignition coil, cylinder 5, activation
The recurrence of misfire codes, particularly in cylinders 3 and 5, suggests a persistent issue. The new code, 0030A4 DME: Ignition coil, cylinder 5, activation, is particularly telling. It directly points to a problem with the ignition system in cylinder 5, specifically the ignition coil. While the initial codes were broader, the appearance of this new code after DME repair helps to narrow down the potential culprits.
As the engine warmed up, the severity of the rough running decreased slightly, but the misfire persisted, especially in cylinder 5. Running a “rough running display” – a diagnostic function available in many scan tools that shows cylinder-specific performance – further confirmed that cylinder 5 was the primary source of the ongoing misfire.
An OBD2 scanner displaying a rough running test, clearly indicating cylinder 5 as the source of the misfire issue in a BMW.
Possible Causes and Diagnostic Steps
Given these symptoms and error codes, especially the 0030A4 code, the most likely culprits for the misfire in cylinder 5 of a 2007 BMW 550i are:
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Ignition Coil: The 0030A4 code directly implicates the ignition coil for cylinder 5. Ignition coils are responsible for providing the high-voltage spark needed to ignite the air-fuel mixture. A failing coil can lead to weak or no spark, resulting in misfires. This is a prime suspect given the diagnostic code.
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Spark Plug: While the ignition coil code is prominent, a faulty spark plug in cylinder 5 could also be the issue or a contributing factor. Spark plugs wear out over time and can become fouled or damaged, hindering their ability to ignite the fuel mixture effectively. It’s often recommended to replace spark plugs when replacing ignition coils, especially if they haven’t been changed recently.
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Fuel Injector: Although not directly indicated by a specific injector code in the later error scans, fuel injectors are a common source of misfires in BMWs. A clogged or failing injector in cylinder 5 might not be delivering the correct amount of fuel, leading to a lean mixture and misfire. Given the initial fuel pressure code (0029F2), fuel delivery issues should not be completely ruled out.
Diagnostic Steps to Take:
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Swap Ignition Coil: A simple and effective diagnostic step is to swap the ignition coil from cylinder 5 with a coil from a known good cylinder (e.g., cylinder 1). Clear the OBD2 codes and restart the engine. If the misfire moves to cylinder 1 (indicated by a new code like 0029D0 DME: Combustion misfires, cylinder 1 or similar), then the ignition coil is indeed the problem.
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Inspect Spark Plugs: Remove and inspect the spark plug from cylinder 5. Look for signs of damage, fouling, or excessive wear. Compare it to a spark plug from a good cylinder. Consider replacing all spark plugs as part of routine maintenance, especially if they are due for replacement.
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Fuel Injector Testing: If the ignition system checks out, the fuel injector in cylinder 5 should be investigated. This can involve more complex diagnostics, such as:
- Injector Resistance Test: Using a multimeter to check the electrical resistance of the injector.
- Injector Swapping (with caution): Similar to coil swapping, injectors can be swapped, but this requires more care and fuel system knowledge.
- Professional Injector Cleaning/Testing: Consider sending the injectors for professional cleaning and flow testing to ensure they are functioning correctly.
Is it Worth Trying a Coil Pack or Plug?
Yes, absolutely. Given the diagnostic codes and symptoms, starting with the ignition coil and spark plug for cylinder 5 is a logical and cost-effective first step. These are common failure points and relatively easy to replace. Addressing these components can often resolve misfire issues, especially when a code like 0030A4 is present.
Going in the Right Direction?
Yes, focusing on the ignition and fuel delivery systems, particularly for cylinder 5, is the correct approach based on the OBD2 codes and rough running symptoms. Systematically testing and eliminating potential causes, starting with the most likely culprits like ignition coil and spark plug, is the most efficient way to diagnose and resolve the misfire issue in your 2007 BMW 550i. If these steps don’t resolve the problem, further investigation into fuel injectors and other potential causes may be necessary, potentially requiring professional diagnostic expertise.
