I've been searching for any help at all on my cold start issue across Google, YouTube, and various N54-related forums, but found nothing consistent with my particualr problem so far. I decided I needed to post my own question. So, just to blow through the usual support questions... I've just completed a fairly thorough resto-mod of my '09 135i M-Sport AT. I've owned it since 2014 (with ~36000 mi), so I can vouch for the majority of the vehicle history. I'll list pertinent details below.
Despite my best efforts, the engine is experiencing rough cold starts (@ 12°-25° C). Symptoms-wise, it's pretty cliche: no codes, rpms surge at startup, no recorded misfires, yet feels like it's missing here and there. There's also a bit of a chassis shudder/vibration, and a sporadic, slight backfire-like sound. I'm sure I smell unburnt gasoline as well. Once warmed up, the engine keeps a rock steady idle (~665 rpm) and runs as smooth as glass. Warm starts have no issues and the engine has heaps of power.
I'm just a fairly experienced hobbyist trying to save money DIY'ing, but I want to get everything sorted. I'm still getting the hang of this platform along and with all the relevant tools. As far as I can tell, my O2 sensors, injectors, lpfp and hpfp are running within spec. I wouldn't ask anyone to figure this out for me, but I wonder if someone would share their thoughts and experience on how to go about a more forensic diagnosis of this problem? I have INPA, ISTA, MHD, and even ProTools. Please see the datalog from a cold start earlier today here. Also of note, I pulled all the plugs 1 hour after the cold start and saw no signs of fuel leakage on the plugs, although the threads did have a fair amount of carbon buildup. Thanks for any help!
Pertinent Repairs/Replacements/Details:
Original stock N54, current odo ~82950 mi, filled w/ Chevron or Shell acn 91 (I know)
As of ~82900 mi
New VRSF N54 aluminumn outlets
New custom Stage 2 LPFP Walbro 450 upgrade
As of ~81600 mi:
MHD Stage 2+ ots tune
XHP Stage 3 v3.0
New Genuine BMW Index 12 injectors x6 (calibrated via ISTA)
New Eldor coils x6
New NGK 95770/5992 (Step 1) plugs, gap=0.20 x6
New hi-temp silicone vacuum hoses and Genuine BMW hard vacuum lines throughout
New OEM serpentine belt, gaskets and coolant hoses throughout
New VTT Stage 1 turbos, upgraded PCV valve, and silicone inlets
New VRSF Charge pipe
New Tial BOV connected via BMS 1/4" BOV vacuum adapter
New BMS DCI
New Pierburg boost solenoids
New Genuine BMW VANOS solenoids + screens
New Genuine BMW MAP sensors x2
New Genuine BMW camshaft sensors
New Genuine BMW crank sensor
New Bosch low pressure fuel sensor
Walnut blasted intake valves
All new fluids: BMW Coolant, Liquimoly Molygen 5W-40 + Genuine BMW Oil Filter
Previous mods:
BMS OCC
VRSF 5" intercooler
N54 Tuning cat-less down pipes
New Genuine BMW rocker cover and gasket (at ~75000 mi)
Despite my best efforts, the engine is experiencing rough cold starts (@ 12°-25° C). Symptoms-wise, it's pretty cliche: no codes, rpms surge at startup, no recorded misfires, yet feels like it's missing here and there. There's also a bit of a chassis shudder/vibration, and a sporadic, slight backfire-like sound. I'm sure I smell unburnt gasoline as well. Once warmed up, the engine keeps a rock steady idle (~665 rpm) and runs as smooth as glass. Warm starts have no issues and the engine has heaps of power.
I'm just a fairly experienced hobbyist trying to save money DIY'ing, but I want to get everything sorted. I'm still getting the hang of this platform along and with all the relevant tools. As far as I can tell, my O2 sensors, injectors, lpfp and hpfp are running within spec. I wouldn't ask anyone to figure this out for me, but I wonder if someone would share their thoughts and experience on how to go about a more forensic diagnosis of this problem? I have INPA, ISTA, MHD, and even ProTools. Please see the datalog from a cold start earlier today here. Also of note, I pulled all the plugs 1 hour after the cold start and saw no signs of fuel leakage on the plugs, although the threads did have a fair amount of carbon buildup. Thanks for any help!
Pertinent Repairs/Replacements/Details:
Original stock N54, current odo ~82950 mi, filled w/ Chevron or Shell acn 91 (I know)
As of ~82900 mi
New VRSF N54 aluminumn outlets
New custom Stage 2 LPFP Walbro 450 upgrade
As of ~81600 mi:
MHD Stage 2+ ots tune
XHP Stage 3 v3.0
New Genuine BMW Index 12 injectors x6 (calibrated via ISTA)
New Eldor coils x6
New NGK 95770/5992 (Step 1) plugs, gap=0.20 x6
New hi-temp silicone vacuum hoses and Genuine BMW hard vacuum lines throughout
New OEM serpentine belt, gaskets and coolant hoses throughout
New VTT Stage 1 turbos, upgraded PCV valve, and silicone inlets
New VRSF Charge pipe
New Tial BOV connected via BMS 1/4" BOV vacuum adapter
New BMS DCI
New Pierburg boost solenoids
New Genuine BMW VANOS solenoids + screens
New Genuine BMW MAP sensors x2
New Genuine BMW camshaft sensors
New Genuine BMW crank sensor
New Bosch low pressure fuel sensor
Walnut blasted intake valves
All new fluids: BMW Coolant, Liquimoly Molygen 5W-40 + Genuine BMW Oil Filter
Previous mods:
BMS OCC
VRSF 5" intercooler
N54 Tuning cat-less down pipes
New Genuine BMW rocker cover and gasket (at ~75000 mi)
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