BMW 740d Power Loss: Faulty Manifold Sensor Alert

Hey there! I have some experience working on cars and had a very similar issue with my 2012 BMW 730d last year. The symptoms you're describing sound exactly like what I went through. Mine also had weak power and was guzzling fuel like crazy. After taking it to my regular workshop, they found a significant vacuum leak. The mechanic did a smoke test and discovered the issue was coming from deteriorated vacuum lines. The whole repair, including parts and labor, cost me 235 Euro. Since then, my 730 has been running like a charm. Before you jump to conclusions about the manifold pressure sensor, can you share any specific error codes you're getting? Also, do you notice any whistling sounds, especially during acceleration? This info would help me give you more targeted advice based on my experience with the 7 series. BTW, have you also considered checking the BMW 750d? My has one and they're known to have similar vacuum system layouts.

Thanks for sharing your experience! I've got 124421 KM on my car and had the last service about 2 months ago. What's interesting is I haven't noticed any whistling sounds like you mentioned, which makes me think it might be different from your vacuum leak issue. I'll definitely get those error codes checked though, that's a smart suggestion. My mechanic did mention something about the turbo system during the last service, so maybe there's a connection there. Have you or anyone else experienced turbo-related issues with these engines? The fuel consumption has really gone through the roof in the past couple of weeks.

Hey again! Yes, I remember dealing with my 730d issues last year. Given what you're saying about the absence of whistling sounds and the recent service mention of the turbo system, this does sound different from my vacuum leak situation. In my case, after fixing those vacuum lines, I actually ran into turbo-related problems about six months later. My fuel consumption shot up similarly to what you're describing. Turned out the turbo wastegate was sticking, which caused inconsistent boost pressure. This matches up with what your mechanic noticed. With 124K on the clock, these issues aren't uncommon, my 730d had around 130K when the turbo started acting up. The manifold pressure sensor could still be part of the equation, but based on my experience, I'd definitely get the turbo system checked out first. The wastegate repair on mine cost more than the vacuum fix, but it sorted out both the power loss and fuel consumption issues. Quick tip though, if you're planning to get it checked, try to note down when the symptoms are worst (cold start, highway speeds, etc.). This really helped my mechanic pinpoint the issue faster. Have you noticed any specific driving conditions when the problems are more noticeable?

Really appreciate the detailed feedback about your turbo experience! That's super helpful, especially since our cars have similar mileage. You've actually made me rethink my initial manifold pressure sensor theory. Now that you mention it, the symptoms are definitely worse during cold starts and when I'm trying to overtake on the highway, exactly the situations where the turbo would be working hardest. I'll make sure to mention this to my mechanic. The wastegate issue you described makes a lot of sense with my symptoms too. While it might cost more than I initially hoped, at least I'm going in with a better idea of what to expect. Think I'll book it in next week and have them focus on the turbo system first. Thanks for sharing all your experiences, it's really helped point me in the right direction!