Recently this 2007 BMW 328i came into our shop from Carlsbad CA. that had it’s check engine light illuminated accompanied by a rough idle and a misfire. After looking throughout the car during our courtesy inspection we proceeded to test the voltage on each ignition coil. In order to complete this we used our ignition voltage checking device and checked the firing voltage of each ignition coil one at a time.
When completing our test we found that all of the coils were working properly except for one. Typically we will see the voltage change on each coil as we are testing them individually, however the voltage should not fluctuate too drastically on each one usually ranging from 9 volts to 12 volts. On the remaining coil that tested bad, we noticed the voltage jumping from around 9 volts, up to 25 volts, down to zero volts, and so on. This was an immediate red flag for us and upon further inspection we not only noticed that the coil itself was a cheap off brand ignition coil , but it also had poor fitment, both of which can cause serious issues!
If you are having issues with a rough idle or suspected ignition coil related misfire, feel free to give us a call or make an appointment online and we would be happy to help diagnose the problems you are experiencing!