Defender TD's Smoke & Power Issues: Fix Needed

I had nearly identical issues with my 2015 Discovery TD last year. The symptoms matched yours exactly, black smoke, power loss, rough idle, and that distinctive hissing noise. Initially thought it was the boost sensor too, but turned out to be a failed waste gate valve. The waste gate wasn't opening and closing properly, causing excessive boost pressure. The fix required replacing the entire waste gate assembly and recalibrating the ECU. It was quite a serious job as they had to remove several components to access it properly. I'd strongly recommend getting it checked soon, running with a faulty waste gate can cause turbo damage if left too long. When I got mine fixed, the mechanic showed me the old waste gate, it was completely stuck due to carbon build-up. Make sure whoever works on it has experience with turbo diesel systems and can properly diagnose before replacing parts. Just sharing my experience, hope this helps point you in the right direction.

Thanks for sharing that! Really interesting about the waste gate valve, it does sound very similar to what I'm experiencing. Did you remember roughly how much the whole repair set you back? Also, just curious, have you had any other issues pop up since getting it fixed? I'm trying to figure out if I should be prepared for any follow-up problems while I'm at it.

Hey again! Just wanted to follow up on my previous post. I took my Discovery TD to the mechanic last week and it turned out I was right about the boost pressure sensor, they found it was faulty and fixed it. While they were at it, they also spotted and replaced the waste gate valve which set me back 860€. Totally worth it though! The car's running like a dream now, no more black smoke, hissing sounds are gone, and the power's fully restored. Been driving it for a few days and honestly, it feels like a completely different vehicle. About your question regarding follow-up issues, I haven't had a single problem since getting it sorted. The engine's running super smooth and the fuel economy's actually improved too. Just make sure you get a proper diagnosis from someone who knows their way around turbo diesels. These symptoms can be tricky to pin down, but once you get the right fix, you should be good to go. Trust me, it's better to get it sorted sooner rather than later to avoid any potential turbo damage. Hope this helps give you a better idea of what you might be looking at!

Thanks so much for the detailed follow-up! Just wanted to update you all, I bit the bullet and took it to a new mechanic yesterday. You were spot on about getting someone who knows turbo diesels. The guy I found was fantastic, really knew his stuff and took the time to explain everything. Turns out it was actually a combination of issues. The main culprit was a clogged EGR valve, but they also found a small crack in one of the boost pipes. Total bill came to about 700 for parts and labor, which wasn't as bad as I feared. Been driving it today and what a difference! No more black smoke, engine's running smoothly, and that annoying hissing is completely gone. Really appreciate everyone's input, helped me avoid potentially making things worse by putting it off. The mechanic said I caught it just in time before any serious damage could happen to the turbo. Lesson learned about regular maintenance, that's for sure!