BMW i8 Engine Problems: Fuel Pump or Something Else?

Hey there! I have some experience working on hybrid vehicles. I actually faced something very similar with my 2015 BMW i3. Initially thought it was the fuel pump too! Turned out it was just a loose connection in the wiring harness that connects to the hybrid system. The symptoms were almost identical, rough running, stalling, and terrible fuel economy. My mechanic found that the cable connection had worked itself loose over time, causing intermittent issues with the power delivery system. The fix wasn't too complex, they traced the connection issue and properly secured the cables. Cost me 95 Euro and the car's been running perfectly since. Could you share what error codes you're getting? That would help narrow down if we're dealing with the same issue. Also, have you noticed any specific patterns when the problems occur, like after driving for a while or right at startup?

Thanks for sharing your experience! Mine's at 50860 KM with the latest service done just two months back. The error codes I'm getting are P0A7F and P0A9C. The issues typically occur right after a cold start, and the car seems to run better once it warms up. However, the stalling during idle is becoming more frequent lately. The loose wiring connection you mentioned is definitely worth checking out, especially since these hybrid systems can be quite sensitive to electrical issues. Did you notice any warning lights on the dashboard before the problem got worse in your case? I'll have my mechanic take a look at the wiring harness first before jumping to fuel pump conclusions.

Hey again! Thanks for those error codes, they're actually really similar to what I had with my i3. When I had the issue, my dashboard was lighting up like a Christmas tree! The main warning lights I noticed were the check engine light and the hybrid system warning, especially during those cold starts you mentioned. Looking at your codes (P0A7F and P0A9C), they're definitely pointing more towards the hybrid system's electrical connections rather than a fuel pump issue. In my case, the warning lights started appearing sporadically at first, and then became more consistent, particularly during cold starts, just like what you're describing. One thing I noticed before getting it fixed was that if I let the car sit for about 10-15 minutes after a stall, it would sometimes run better temporarily. This was another clue that it wasn't the fuel pump, since fuel pump issues usually don't "fix themselves" temporarily like that. I'd strongly recommend having your mechanic focus on the wiring harness, particularly around the hybrid battery connections. My repair guy said these connections can work loose over time due to normal vehicle vibration. Since you're at 50860 KM, that's definitely enough mileage for this kind of issue to develop. Keep us posted on what they find! I'm really curious to know if it's the same problem I had.

Thanks everyone for your responses! After reading about your similar experiences, I think I'll definitely have my mechanic prioritize checking the wiring harness and hybrid system connections first. It's reassuring to hear that it might not be the fuel pump after all, which would've been a much more expensive fix! Just called my mechanic and booked an appointment for tomorrow morning. I mentioned the wiring harness issue and the error codes, and he agreed it sounds more like an electrical problem than a fuel system issue. He's worked on quite a few hybrid BMWs, so hopefully he can sort this out quickly. I'll definitely keep you all updated once I get the diagnosis. Really appreciate everyone's help, it's saved me from potentially focusing on the wrong problem. Thanks again for sharing your experiences and technical knowledge. Will post an update once I know more!