I fixed a misfiring engine. Story inside.
Two weeks ago, on Sunday, I drove my dad's BMW 330xi to meet up with the rest of the family at a restaurant, after I helped a friend solve an issue remotely over Skype. The car was running fine that night. However, the next morning, the car was having trouble starting (due to the original battery), and once started up, ran really rough. Luckily for my father, who doesn't have to drive to work, can do meetings from his office in the basement. My father questioned me that evening, asking if I did anything stupid with the car (such as redlining while cold), and I told him I kept it under 3000 RPM.
The car sat for a week, and the battery died as well due to the cold weather, so I hooked up a battery charger for a bit. Nearing the end of the week, I told him to look up parts. I told him about Hosie & Brown, a local shop recommended by a professor at college, he decided to order a new battery and an ignition coil on Monday, and he sent my mother to pick it up, while I was busy at college.
Fast forward to today, on Wednesday, one and half weeks after the engine started misfiring, my godfather lent his garage so we could do work, It is a new house, and the garage was well insulated, opposed to our garage, which isn't. The 3 KM drive there felt like torture on the engine, despite being at low RPM. Once we got there and started working, my father and I discussed on how the plastic cover was secured, I just started tapping on one of the fake "screws" securing the cover down, and something didn't feel right about the screw I tapped on. I decided to gently tug on the cover and eventually pull it off, despite my father's warnings that I would break it off. Turns out it was only held on by some pins and some rubber rings, (same as a guide to do the same procedure on a BMW 5 series of the same year I saw on YouTube).
I noticed an oil leak pooled up on the engine around the ignition coil, and my father and I thought it was related to the coil malfunctioning. We were wrong. The coil was dry, no oil dripped inside at all.
You can see the shot below has the new coil next to an engine full of the older ones.
After we cleaned the pooled oil up, we plugged the new coil in, and started the car up, it didn't run rough at all, and it ran much better than before.
For a comparison,