I have read about every thread out there on this. I have been having an issue where it was rough idle, after a bit it would clear up then turn the car off, restart and it was fine. This last week, it wouldn't clear.

Started troubleshooting it using some of the previous threads. I checked the fuse, then started checking the low pressure pump pressure. I used a fuel line off my donor car to adapt my brothers fuel gauge kit to work on it. Everything tested fine there. Put it back together and everything worked fine. I took it for a test drive to try to try to get it to throw a code and notta. High pressure was right where is should be. Stomped on it for about 15 minutes, wouldn't throw a code.

Was gone this AM, got home a bit ago and checked it. Went limp mode right away, Turned it off then back on and everything was fine. Could I have a bad O-ring if the flex fuel line? It acts like it is losing its prime.

 

BTW, 2012 R58 Coupe S, N18

 

Is there a reason you think the misfire is fuel pressure related? Sounds like hooking up a MB-specific (or fully capable) bidirectional scanner would be the prudent thing to do...

 

Sorry, I had scanned it using Bimmerlink. I got
2BEE high fuel pressure, plausibility, cold start pressure too low
After removing the supply line to the HPFP and replacing it with a line with a gauge, I tested the LPFP which was fine 75 PSI and maintained. Put the original fuel line back on and everything was fine, no codes etc. I tried everything I could do to make it throw a code. The next day, approximately 14-15 hours later, it had the cold start issue again.

The way those quick couplers work, I question if air isn't getting into the line and causing the issue.

When everything is working HPFP is well within pressure specs, monitored with Torque Pro via ODB. I don't think a bad HPFP would have bad/low pressure one moment, good the next. Every type pump I have ever been around they either work right or don't.

 

I wonder if you could be dealing with air in the lines as well. Seems like if that was the case, the LPFP could achieve the correct pressure, but if the engine end of the lines were full of (pressurized) air, you're going to have a long crank issue, until the air cleared the line.

Here's what I found relative to your error (I'd look closely at that fuel rail pressure sensor, or maybe more likely, the HPFP - having one that's flaky doesn't sound all that unlikely)...

2BEE High-pressure fuel system, cold start: Pressure too low
Possible fault causes:
-Tank Empty
-Defective rail-pressure sensor
-Defect in low-pressure system
-High-pressure pump defective

 

The rail pressure was my next guess culprit. If it is goofy and sending incorrect data, the computer throws a code. I have a new fuel line coming so will see what that does. Trying to replace the low $$$ things first.

I have my doubts it is the HPFP. When everything is working correct after shutting down and re-starting, the pressures are right where they should be. It drives fine until it sits for more than 4 hours. Most failing pumps (gear or diaphram) either work or they don't. Once it is started and ran for a couple minutes, turned off then restarted it runs fine. Like I say it is like it is losing its prime.

 

Have you changed the fuel filter? I just had a thread about a no start diag. Ended up being the filter. Cheap and easier preventative maintenance item as well.

 

I want to check that this coming weekend. It isn't quite as easy on a R58 Coupe, no back seat.

 

I have the filter but haven't installed it. If you research what it takes to replace one in a R58/59, you will know why.

I bought a new HPFP from ECS and installed it this last weekend. That was the issue, no problems since. Much easier to do than I imagined. The diaphragm on the old one is definitely the issue when you look inside.

Since it is rolling 100,000 soon, I will change the fuel filter, just have to figure a day to do so.