Infiniti Q Diesel: Black Smoke & Power Loss Mystery

I had a similar issue with my 2014 Infiniti QX70d last year. The symptoms you're describing are exactly what I experienced rough idle, black smoke, and that distinctive whistling noise under acceleration. Took it to my mechanic and it turned out to be a faulty electrical bypass valve on the turbo system. The valve wasn't regulating boost pressure properly, which explained all those symptoms. It was actually a pretty serious issue that needed immediate attention because it was causing excessive fuel consumption and could've damaged the turbo if left unfixed. The repair involved replacing the entire bypass valve assembly and recalibrating the ECU. Had to leave the car at the garage for two days while they sorted it out. Since the fix, the car's been running smooth as new no more smoke, weird noises, or power issues. If you're in the same boat, I'd strongly recommend getting it checked out soon. These symptoms typically don't fix themselves and could lead to bigger problems. I can recommend my mechanic if you're in the area he specializes in Infiniti/Nissan diesels.

Thanks for sharing your experience! That's really helpful as it sounds exactly like what I'm dealing with. Quick question do you remember roughly how much the whole repair set you back? And has everything been running smoothly since the fix, or have you noticed any other issues pop up? My wallet's still recovering from my last mechanic visit, so I'm trying to get an idea of what I'm in for!

Hey again! Yeah, happy to help out. Since getting my QX70d fixed, it's been running like a dream! The whole repair job came to 250€ to sort out the electrical bypass valve, and they also spotted and fixed a dodgy boost pressure control position sensor while they were at it. Honestly, it was worth every penny haven't had a single problem since then. The black smoke's gone, no more weird noises, and the engine's running super smooth. It's like having a different car! I totally get what you mean about being worried about costs mechanics can sometimes hit you with scary bills. But in this case, getting it sorted sooner rather than later definitely saved me from bigger problems (and probably bigger bills) down the line. If you decide to get it checked out, at least now you've got a rough idea of what you might be looking at cost-wise. Hope that helps! Let me know if you need anything else.

Thanks so much for all the details! I actually bit the bullet and took it to a mechanic yesterday. You were spot on it was the bypass valve causing all the drama. Ended up costing me about 300€, a bit more than yours because they had to order in a specific part for my model. Got the car back today and wow, what a difference! No more black smoke show when I accelerate, the weird whistling's gone, and it's running super smooth again. Feels like I've got a new car! Guess sometimes you just have to trust the experts and get these things sorted, even after a bad experience. Really glad I didn't wait any longer mechanic said it could've gotten pretty expensive if I'd let it go. Thanks again for helping me make the decision to get it checked out. Sometimes it just helps knowing someone else has been through the same thing! Take care!