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Originally Posted by BMWJU
Hello im new here! and to the n54 platform i am familiar with BMW'S as ive had many e46s, F30 n20,e90 n52's IM having the same issue IM MHD stage 2+ FBO no outlet/inlet i got the car stock in limp mode i bought at 132k now it as 134k once i added bolt ons and found out MY VSRF charge pipe was causing 30ff code switched to arm charge pipe it fixed issue but added more issues with fueling that's how i found out my injectors were bad/leaking replaced with new ones i changed most maintenance items(prone to fail components) ex( HPFP used unsure of miles, INDEX 12 i changed them between different sets to ensure that wasn't the issue, LPFP STAGE 2 precision race works & Also converted back to stock fuel pump as of now did not fix issue, step 1 colder sparks triple checked GAP there new, Coil packs, fuel regulator, VANOS solenoids, PCV) everything else i replaced shouldn't affect cyl 6 im getting 29D2 & 29D9 my good friend/mechanic says maybe my hpfp is capable of stock maybe stage 1 power not stage 2 plus power i have not tested this theory out as i just found this issue and have work, My car drives OK in drive maybe 30% throttle it may bog a little any more it will misfire it will stutter like im hitting the bumps on the side of the freeway only CYL 6 if i go in sport it will stutter even worse as of now driving in "D" it goes to moderate speeds i cannot do a quick overtake incase of bad drivers or merging onto freeway or i will misfire plz help! IM not sure how this relates to you but my rail pressure averages about 680-720 i went in my buddies car custom tune FBO upgraded turbos stock fueling other than index 12 his averages 720 minimum average it goes low but never like mine is it my HPFP?
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It is very difficult to read a post like this, without adequate punctuation.
I've heard that the stock HPFP will work fine with a stage 2 tune. However, your pump is certainly showing typical signs of failure. My pump didn't fail catastrophically, it just became weaker and weaker, suddenly dropping to a lower pressure when demand increased, then throwing codes and limp mode.
The output pressure constantly varies according to demand. You should not be looking at average pressure, but at maximum pressure. Use a live scanning tool to monitor the low-pressure and high-pressure values simultaneously. They should track each other with a multiplication factor of about 10x. When the turbos are in full boost at mid-high RPM, you should be seeing pressures sustained at well over 2000 psi. My pump would reach those pressures temporarily, but would suddenly drop out under load.
Make sure you replace the pump with a new one of the latest design. Do not risk the cheap eBay/Amazon pumps that are poorly refurbished pumps, likely from the obsolete first revision.