SOLVED Another N54 Cold Start Dilemma

KAR

New Member
Oct 2, 2020
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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)
 
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KAR

New Member
Oct 2, 2020
3
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I guess this will have to due as just a blog to myself. Hopefully someone in the future may come across it and benefit. After racking my brain for days; and simply listening to/observing my engine, I concluded that the engine was acting flooded upon start-up. No special diagnostic tools required, just a gut feeling. In the end, I solved my cold start problem. Despite initially following recommendations to upgrade to colder NGK plugs from various reputable sources, good 'ole Bosch 0242140507 (aka BMW ZGR6STE2) plugs work the best. No worries about adjusting the gap and cold starts are perfect.

At least for my application, both the NGK 1 Step and 2 Step colder plugs sucked (I tried both). Total waste of money! I can only guess at this point, that given I "only" have new Eldor coils, they must not be powerful enough to generate a strong enough spark to handle burning off the rich fuel mixture occurring during start-up. Maybe colder plugs are only necessary when you upgrade to high performance coils (e.g., BimmerLife or Precision Raceworks)? Please comment if you've had similar experiences or have other theories as to why factory Bosch plugs work better then colder NGKs.
 
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Neg89

Private
Jul 4, 2021
40
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Hi.Is there any updates on this. ? Upgraded Lpfp and put in new hpfp and nothing changes,my hpfp drops below 1000psi at wot in midrange, .Maybe i have problem in pressure regulator?