BMW Ignition Coil Problems

Have you ever been cruising down the highway in your powerful BMW, only to feel a sudden jolt, hear a misfire, or experience an unexpected loss of power? If so, you just might be one of the many BMW owners who have encountered ignition coil problems. 

BMW ignition coil problems, especially, engine misfire, rough idling, hard starting, etc. have panicked many owners. An issue as commonplace yet enigmatic as BMW ignition coil issues warrants a deep dive into its causes, symptoms, and solutions. 

So, whether you’re a DIY mechanic with greased hands or a casual driver hoping to understand what’s happening under the hood, this guide is for you. So buckle up and prepare for an intriguing journey into the heart of your vehicle’s engine.

BMW Ignition Coil Problems

BMW Ignition Coil Problems

Ignition coil issues have been reported frequently in several models including the E46 and E90 series so don’t be surprised if you have a ‘coil light moment’. Therefore, understanding and addressing your BMW Ignition Coil Problems on time is critical. So, let’s jump onto the core discussion. 

Rough Idling

Ignition coil failure, often signaled by rough idling, is a prevalent issue in vehicles. This particular problem has been a source of worry for numerous BMW owners over the years. Those who are unaware often mistake it for a fuel-related issue. 

The problem typically arises when minor cracks form on the circuit board or when small components detach themselves, disrupting the electrical flow and leading to ignition coil failure. When this occurs, the vehicle’s engine may stutter, stall, or even fail to start. 

Many drivers also report that their vehicle seems to jerk or hesitate while accelerating, which is a telltale sign of ignition coil failure. 

To diagnose this issue, mechanics often rely on diagnostic tools that can read fault codes stored in the vehicle’s computer system. These fault codes can point directly to an ignition coil failure or any other relevant issues.

Engine Misfire

Premature failure of ignition coils, specifically in BMW models from 2001 to 2004, can lead to engine misfires and substandard performance. These problematic coils, produced by Bremi, are susceptible to elevated temperatures within the engine compartment which increases their likelihood of failure over time. 

A malfunctioning ignition coil can create various issues for your car, including erratic misfires, rough idling, decreased fuel efficiency, engine hesitation, and emissions complications. If these issues are disregarded, they may escalate into substantial engine damage. 

The first step includes diagnosing the issue by looking for common signs such as a check engine light, poor acceleration or even stalling. Once identified, replacing these faulty Bremi coils with more reliable alternatives can significantly enhance your vehicle’s performance and longevity.

Difficulty Starting the Vehicle

Have you ever experienced the distress of being stranded, and unable to start your car? This is an unfortunate circumstance that numerous BMW owners have encountered. The issue arises when the positive wire is disconnected from the coil; it receives 12v when the key is in the start position, and 10v during cranking, both of which are correct. 

However, upon reconnection to the coil, it only receives a mere 2.6v in both situations. This low voltage is insufficient to reach the spark plugs effectively, thus making it challenging to initiate vehicle ignition.

When your car stalls or refuses to start, you might immediately think that it’s a battery or starter motor problem. However, this is often not the case with these BMWs. 

Troubleshooting the issue on your own can be a tough job. However, if you’re confident enough, follow the steps. Begin by detaching the battery and the DME cable. Subsequently, follow these steps: 

  1. Unplug the coil negative and examine the continuity from this connector to DME pin 1. Confirm that there is an open circuit from DME pin 1 to the ground. 
  2. Measure the resistance between DME 47 & 48, which should fall within a range of 500-560 ohms. If you unmount the CPS, observe that when a ferrous object approaches the sensor face, resistance shifts from approximately 500 to between 540-560 ohms. Ensure neither pin is grounded.
  3. Inspect for continuity from DME 36 to main relay 85 and from DME 3 to fuel pump relay 85. 
  4. Confirm the power supply at DME pins 18, and 27, and main relay pins (86 &30). The power supply to pin18 comes directly from the main relay which also supplies power to injectors and fuel pump relay.
  5. Confirm that there’s a power supply at both coil positive terminals as well as fuel pump relay pin3 0. Both receive switched power directly from the ignition switch via a C101 connection.

What Causes Ignition Coil Issues in BMW?

In contrast to many older vehicles that utilize a distributed spark ignition, modern engines feature an individual ignition coil for each spark plug on every cylinder. 

These coils receive a precisely timed signal from the engine control computer, which then activates the respective spark plug to ignite the fuel and air mixture within the cylinder. A malfunctioning ignition coil typically results in a single-cylinder misfire and triggers the check engine light. 

Similar to standard turbochargers, the Mitsubishi TD04 turbo can achieve up to 250,000 RPM at full throttle, making lubrication crucial for maintaining the turbine shaft at such high speeds. Regrettably, most of the failures we encounter are due to oil starvation. 

When a turbo lacks sufficient oil, its center bearing begins to wear down against the turbine shaft. This can eventually lead to complete wear-through, causing one or both ends of the shaft to dislodge and move erratically within the housing – creating an unpleasant noise and inflicting further damage on the interior components of the turbo housing.

How to Fix a Bad Ignition Coil in BMW

Sadly, the ignition coils in BMWs are not repairable and require replacement when their circuitry malfunctions. It’s advised against operating your vehicle with a defective ignition system; it’s not just unsafe, but it could also harm other parts of your engine. 

If you suspect an issue with an ignition coil, your first step should be to inspect and test the elements of the ignition system to identify the core issue. Should the coil prove faulty, it will need to be removed and replaced. 

Since ignition coils and spark plugs function in tandem, it is generally recommended to replace both components simultaneously for optimal performance. However, depending on your BMW’s specific system, swapping out the spark plugs may not be required.

Ignition Coil Replacement Process

The process of swapping out faulty ignition coils on your BMW is relatively straightforward, particularly when trying to troubleshoot a misfire. Adhere to the subsequent instructions carefully to complete the task independently. 

Step 1: Uncover the Engine

Initiate by taking off the engine covers and any other elements that may hinder your access to the injectors. As these injectors are compatible with a broad spectrum of BMW variants, this procedure will vary for each individual.

Step 2: Isolate Each Coil Sequentially

With the vehicle in operation, disconnect the wiring connected to the ignition coil of cylinder number one. Pay attention to any alterations in sound while it’s idling. If there isn’t an audible change, then you’ve identified cylinder number one as the issue. 

However, if there is a significant variation in sound or engine performance, it indicates a problem with another cylinder. In such instances, proceed sequentially until you locate the faulty cylinder.

Step 3: Detach and Swap Coils

After identifying which ignition coil might be causing trouble, validate your suspicion by exchanging it with another known functional coil. Labeling the defective coil will help you keep track of its new location and avoid confusion.

Step 4: Examine Coil Boots

While swapping ignition coils, take some time to scrutinize the boots for any defects. Even minuscule holes or rips can lead to grounding problems rendering that particular ignition coil useless. 

For instance, during our inspection of a BMW model, we found a tiny hole in the boot of cylinder number one’s coil. Since you’re already engaged in this process, we advise procuring your vehicle-specific kit and replacing all ignition coils simultaneously.

Step 5: Fit New Coils and Reassemble 

Whether you’re substituting just one or all coils, the procedure is straightforward and swift. Apply a minimal amount of dielectric grease inside the coil boot; this will facilitate their removal in future instances. From here on out, you’re simply positioning your coils onto your plugs, reconnecting the wiring system, and reattaching your engine covers.

Final Words

BMW ignition coil problems are not uncommon and can cause significant performance issues if left unchecked. The symptoms of failing ignition coils, such as misfires, poor fuel economy, and reduced horsepower should never be ignored. Regular servicing and using high-quality replacement parts can significantly reduce the risk of these problems occurring. 

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