Odd Fueling Issue


New Member
Mar 23, 2023
Boulder, Colorado
2010 e61 535xi
Hey guys, new to BMWs in general. Just picked up a grandpa-special e61 535xi with 130k on the lock and have run in to some interesting issues within my (very brief) period of ownership.

To start:
Twice in the same corner the car has cut power and started misfiring like crazy. Both times a simple reset (of variable length--the first time I let it sit for about 15 minutes and the other I immediately restarted it) has "fixed" the issue.

I got two codes: 29DC and 29F2. Very much associated with HPFP failure...except my rail pressures seem fine.

2nd and 3rd pull logs for reference. 91 octane, totally stock motor, MHD stage 1. Just got done with a bunch of routine/necessary preventative maintenance so I thought it'd be fun to see what the N54 is capable of with no supporting mods at all. Am planning on doing FBO+PS2 within the year (chasing a "reliable" ~450-500whp on pump). So this is baby steps to see what I need to do to get this thing all the way there.

Now, I'm noticing a few things:

- STFTs have a huge delta in boost
- Mild timing retardation on nearly all cylinders (as high as 6deg in some cases)
- Pretty extreme boost spike(s) off throttle, more than likely unrelated and boost solenoids are already on my list of todos
- Insane AFRs on decel (though I've heard this is "normal" for MHD)
- Running somewhat(?) lean
- Rail pressure seems good (as previously mentioned), low-pressure seems a little wonky(?)
- Nothing else stands out as particularly "weird" or "wrong" (to me, at least)

Now, to get this out of the way:

- The HPFP was replaced within the last 10k miles (again granpda owned--he made sure to make use of his extended warranty)
- The valve and oil pan gaskets were done about 2k miles ago (right before he allegedly traded it in for an X5) and with the valve cover coils, plugs, injector clean, and intake valve media blast
- To my knowledge nothing has been done with the LPFP
- Or the pressure regulator
- Leakdown and compression test were good, no smoke coming from the oil cap or anywhere else
- No weeping injectors, oil is clean and as vicious as you'd like it to be (no smoking or any other indications of issues either)
- Fuel pressure sensor has never been touched (already have one on the way just to see if that does anything)
- Boost solenoids are original as are knock sensors and O2 sensors

Here's a video of the pressure regulator sounding like ass (or at least I think it sounds like ass).

Might start there if the pressure sensor doesn't help. Is there anything else I should be looking at immediately doing (other than re-flashing the stock tune, which I'm doing ASAP)? Any personal experience or sage advice? Let me know, I'm super excited to be part of this community!