BMW 5 Diesel Misfiring, QDC Issue or Something Else?

Hi there! I have some experience working on cars and had a similar issue with my 2015 BMW 3 Series diesel (I also own a 1 Series). Had exactly those symptoms, rough running and misfires. Turned out one of my injectors was faulty. After diagnostic tests, my mechanic found the injector wasn't delivering fuel properly. Got it replaced and it cost me around 515 Euro, but the car's been running smoothly since then. Could you share more details about when these symptoms occur? Like is it worse when the engine is cold or under load? Also, are you getting any specific error codes? This would help narrow down if you're dealing with the same injector issue I had. Hope this helps! Let me know if you need more info.

Thanks for sharing your experience! My issues mostly happen when the engine is cold, especially during the first 10-15 minutes of driving. After that, it tends to run a bit smoother but still not perfect. Haven't pulled the error codes yet since my OBD reader is acting up, but planning to get that sorted this week. I've been keeping up with maintenance (last service was just 2 months ago at 108587 KM) but this is my first major issue with the car. I'm hoping it's just an injector like in your case and not something more serious. Did your mechanic mention anything about cleaning the injectors first, or was replacement the only option?

Hey again! Yeah, I totally get what you're describing, those cold-start symptoms sound exactly like what I dealt with on my BMW 3 Series. When my mechanic looked at it, we actually did try cleaning the injectors first because it's obviously the cheaper option. Cost me about 150 Euro for a professional cleaning service, but honestly, it only helped for like a week before the problems came back. That's when we knew we had to bite the bullet and go for the replacement. One thing my mechanic pointed out was that with these modern diesel engines, once an injector starts acting up, cleaning rarely fixes it permanently. They're such precise components that when they start to fail, replacement is usually the best long-term solution. Since you mentioned your car's mileage, I should add that mine was showing similar symptoms around the 120,000 KM mark. These diesel injectors typically start showing their age around that point, so the timing makes sense in your case too. Quick tip from my experience, while you're getting those error codes checked, ask them to specifically look at the fuel rail pressure readings. That's what ultimately confirmed my injector issue. Would love to hear what codes you get when you manage to check them.

Thanks so much for all this detailed information! This really helps put my mind at ease about what I'm dealing with. Interesting to hear about your experience with the injector cleaning, definitely good to know it might just be a temporary fix. I've booked the car in at my regular mechanic for next Tuesday, and I'll make sure to ask them about checking the fuel rail pressure like you suggested. I'll probably skip the cleaning attempt and go straight for replacement if they confirm it's an injector issue. No point wasting money on a temporary solution, especially if it's likely to fail again soon. The car's been good to me so far, so I guess it's just time for some maintenance. I'll update the thread once I get it sorted out, might help someone else with similar issues down the line. Really appreciate you taking the time to share your experience with this!