How To Diagnose And Replace Bad Ignition Coils On Your BMW
Direct ignition coils are a common failure item in a vehicle's ignition system. How do you truly know if your vehicle's misfire is due to ignition coils? An engine misfire can be so many things. Ignition, electrical, mechanical, the list goes on and on. Gareth Foley, our BMW Catalog
Tools needed to complete this repair:
- OBDII Scan Tool (Optional)
- Underhood LED Light (Optional)
- Screwdriver Set (Optional)
- Dielectric Grease
Parts needed to complete this repair:
Step 1: Diagnostics
In our case, diagnostics is simple. Our F30 BMW had a check engine light and was idling noticeably rough. If you have a cylinder misfire, you should have a check engine light on. If you own a scan tool (which we highly recommend if you own any OBDII cars), now would be the time you plug it in to check which cylinder is misfiring. On our BMW, our scanner shows that we have a misfire on cylinder number one. If you're using a scan tool, you can skip ahead to step five.
Step 2: Remove Engine Covers
Start by removing engine covers and anything obscuring access to your injectors. Since these injectors fit a wide range of BMW models, this process will be different for everyone.
Step 3: Disconnect One Coil at a Time
While the car is running, disconnect the wiring to the cylinder number one ignition coil and listen for a change in sound at idle. If there isn't a discernible change in sound, you know that cylinder number one was the problem. If there was a noticeable change in sound or the operation of the engine, you know it was a cylinder other than number one. If that's the case, continue down the line until you find your problem cylinder.
Step 4: Remove and Alternate Coils
Once you've honed in on which ignition coil is the potential culprit, you can confirm this by swapping that coil with one you know is properly functioning. Making a mark on the bad coil will make your life easier as you can easily lose track of what cylinder you moved it to.
Step 5: Inspect Coil Boots
While you're alternating ignition coils, you might as well inspect the boots for imperfections. Even the smallest hole or tear will cause a grounding issue - making that ignition coil ineffective. Here on our BMW, cylinder number one coil had a pinhole in the boot. Since you're already here, we recommend purchasing your car-specific kit and replacing all of your ignition coils at the same time.
Step 6: Install New Coils and Reassemble
Whether you're replacing just one coil or all of them, the process is quick and simple. Apply a very small amount of dielectric grease to the inside of the coil boot; this will make them much easier to remove in the future. From this point on you're just seating the coils on your plugs, reconnecting the wiring, and reinstalling your engine covers.
Testing and replacing problematic ignition coils on your BMW is one of the easier processes when diagnosing a misfire. If you're wondering which ignition coils you specifically need, click the link below and use the "My Garage" vehicle search. And as always, make sure to subscribe for more videos