BMW 840d Timing Chain Issues Causing Multiple Problems

Hey there! I have some experience with BMWs, faced something very similar with my 740d (2020). When I first noticed these symptoms, I also got worried about potential timing issues. Turned out it was indeed the crankshaft position sensor playing up. Had the same symptoms, engine light, power loss, weird startup sounds, and the car was drinking fuel like crazy. My trusted mechanic diagnosed it pretty quickly and replaced the sensor. Cost me around 340 Euro total, but it fixed everything, performance came back to normal and all those error codes cleared up. Before jumping to conclusions though, could you share: How many miles/kilometers on your 840d? Are you getting any specific error codes? Does the metallic sound go away after the engine warms up? With this info, I might be able to tell if it's the same issue I had. Also, since these BMWs can be tricky, I'd recommend having it checked by a specialist who knows their way around the B57 engine. Better safe than sorry!

I've got 51020 KM on mine and just had it serviced recently. I'm getting error codes P0365 and P0340, and yes, the metallic noise does disappear after warm-up. I started noticing this about a week after my last service, which makes me wonder if something wasn't properly adjusted during maintenance. Just curious, did your mechanic check the timing chain tensioner as well when they replaced your sensor? I'm thinking of having both looked at while they're in there, just to be on the safe side.

Hey again! Actually, you mentioning those specific error codes (P0365 and P0340) is giving me flashbacks to my experience. When my mechanic dug deeper into my 740d, they did check the timing chain tensioner, good thinking on your part! In my case, while the crankshaft position sensor was the main culprit, they found that the tensioner was showing early signs of wear too. I decided to have both replaced since they were already working on it. Honestly, it was a bit more expensive (ended up around 520 Euro total), but it gave me peace of mind. The timing of your issues, right after a service, is interesting. The same thing happened to me! Turned out during my service, they had to remove some components to access other parts, and something wasn't properly reconnected. That's why I always stress about finding a mechanic who really knows these engines inside out. From what you're describing, it sounds almost identical to what I went through. My advice would be to definitely get both the sensor and tensioner checked. These B57 engines are fantastic but they can be quite sensitive to timing issues. Better to sort it all out at once than have to go back in there again later. Let me know what you find out, I'm curious if it's the same issue I had!

Thanks so much for sharing your experience! This definitely helps explain what I might be dealing with. You've honestly made me feel a bit better knowing I'm not alone with these symptoms, and having a real-world example of the fix is super helpful. I've just booked it in with a BMW specialist for tomorrow morning. Going to have them check both the sensor and tensioner like you suggested. You're right, might as well do both while they're in there. I'll probably be looking at a similar cost to what you paid, but it's worth it to get everything sorted properly. Really appreciate you taking the time to share all these details. I'll definitely update once I get it fixed. Fingers crossed it's as straightforward as your repair was! Thanks again for the help!