[Lilquan]

Hello i was wondering if anyone knew what is going on in this video. Car is 2015 m235i. When flashed back to stock the issue goes away. I have no where to turn to. My mechanic says nothing is mechanically wrong and tuner says they don't know what's going on after sending a test map. no codes or check engine light. burbles also sound weaker than in the past. issue only arises on cold start....
Fabspeed sport cat
vrsf intercooler and charge pipe
precision racewalks 2.5 lpfp
dorch stage 1 hpfp
bm3 stage 1 multimap running e30 ethanol mix
Brand new MAF sensor.
h&r springs
k&n air filter

[1slow2_]

Originally Posted by Lilquan

Hello i was wondering if anyone knew what is going on in this video. Car is 2015 m235i. When flashed back to stock the issue goes away. I have no where to turn to. My mechanic says nothing is mechanically wrong and tuner says they don't know what's going on after sending a test map. no codes or check engine light. burbles also sound weaker than in the past. issue only arises on cold start....
Fabspeed sport cat
vrsf intercooler and charge pipe
precision racewalks 2.5 lpfp
dorch stage 1 hpfp
bm3 stage 1 multimap running e30 ethanol mix
Brand new MAF sensor.
h&r springs
k&n air filter

I had this a couple months ago. Check, clean and tighten the maf sensor on the charge pipe and intake. Could be different situation for you but that was the problem for me

[rtl32]

Mine also did that. MAF maintenance seems to help. Went away for good after an injector failed and I replaced it. Came back for a few starts when it got cold overnight again (50s, changed from the 70s) O filled up with E40 again, and has since been gone completely.

Super weird. Just like my p0171 code that only triggers when idling. Might have something to do with aftermarket intakes (both the start and code)

[XutvJet]

With a fully warmed engine and the car in neutral, disconnect the MAF sensor and let it run a few minutes. Shut the car off and reconnect the MAF sensor. On the next cold start, the issue should likely be fixed.

[rtl32]

Originally Posted by XutvJet

With a fully warmed engine and the car in neutral, disconnect the MAF sensor and let it run a few minutes. Shut the car off and reconnect the MAF sensor. On the next cold start, the issue should likely be fixed.

Fixed for one cold start, or for a while? Do you know how this works?

My guess is you're hinting towards the MAF open loop reading on cold start is somehow causing a malfunction off its first readings, so you tell the car to run closed loop, and then next time it starts it starts in closed loop and doesn't happen until it figures out the MAF is back again. I don't see how that would reset anything more than for the first cold start afterwards.

[rtl32]

Guys I figured it out.

Leaky injector tips.

I narrowed down this problem in my car to only happen after a certain amount of time parked, but not after a certain amount either. So a window between like 7-15 hours parked it would do this. I'm guessing that this is the window in which the leaky injectors I had would begin draining, and then after this would be fully depressurized.

Before this window = great starts no hiccup.
In this window = hiccup almost every time.
After this window = takes a crank or two more but great starts with no hiccup every time.

I suspect this is because in the starts where it had been sitting for a long time, the injector leaked all the pressure from the fuel rail and it just took another crank or two to fully depressurize the system. Before the window, it would not have leaked significantly. During the window, each cylinder could have different fuel pressures during start - hence the stumble and over rev correction.

I noticed my car began stumbling during low load and low rpm operation, similar to normal cold operation before full warmup on E. It just didn't feel right. This would be instantly corrected by just giving it a little more gas suddenly. I also noticed a slight increase in gas smell during cold starts during the hiccup window.

I decided to replace all my injectors at once suspecting laggy and old injectors.

All 6 swapped, stumbling gone, cold starts are perfect, gas mileage is better and no more raw gas smell (impressive considering I'm almost straight piped). The injector tips were nasty, who knows what kind of terrible pattern I was working with. Car runs MUCH smoother, revs more freely, is more responsive, and the butt dyno is saying it may even be more powerful now as well. The wife could even notice it (she can't tell the difference between 93 and E30 tune from the passenger seat!).

There is a steal of a deal for 6 new injectors on the bay right now. Search up set of six 68286 bosch injectors by parts container. They shipped me 1 at first but made good by sending me 6 more. Kind of a pain in the ass but much cheaper than anywhere else.

[XutvJet]

Did you try my MAF disconnect first? That seems to fix it for most people including a guy on this forum just today. Your issue looked exactly like mine which was fixed with the MAF disconnect.

[rtl32]

Originally Posted by XutvJet

Did you try my MAF disconnect first? That seems to fix it for most people including a guy on this forum just today. Your issue looked exactly like mine which was fixed with the MAF disconnect.

For a start or two yes, didn’t help the low load stuttering though just the initial dip. I replaced MAF during initial assessment of this issue, and have cleaned/inspected it every oil change since. I think mafless might take out some of the cars initial internal feedback during which the poor injector issue causes it to dip, and the mafless reset causes it to default to some richer cold start fueling scale which fixes it but playing with it every other cold start is not practical.

I’m at 62k so injectors were well needed anyway. Fueling is kind if important so I wouldn’t err on the side of it being solely MAF, for the cars sake.

[XutvJet]

Originally Posted by rtl32

For a start or two yes, didn’t help the low load stuttering though just the initial dip. I replaced MAF during initial assessment of this issue, and have cleaned/inspected it every oil change since. I think mafless might take out some of the cars initial internal feedback during which the poor injector issue causes it to dip, and the mafless reset causes it to default to some richer cold start fueling scale which fixes it but playing with it every other cold start is not practical.

I’m at 62k so injectors were well needed anyway. Fueling is kind if important so I wouldn’t err on the side of it being solely MAF, for the cars sake.

I only had to disconnect the MAF one time ever to remedy the issue.

The injectors in these cars should last 150K+ miles and aren't the unreliable units like those used in the N54 cars. However, things happen and parts can fail. I just find odd that you had the same exact cold start issue (no issues with hot starts) as myself as a number of people on this form, the M2 forum, and the 3/4 series forum. I believe all reported cases were remedied with time (people just let it work itself out), they disconnected the MAF, and a minority threw a number of parts at it like MAFs, coil packs, spark plugs, and/or the HPFP. You're the first I heard that's swapped injectors.

Did you determine that an injector was really leaking or just assumed it was since the issue didn't reappear after the replacement? I find it odd that a leaky injector would be the culprit because on a stone cold start, a ton of fuel is being injected and it's already super rich. It wouldn't explain why the car starts just fine and then momentarily almost stalls. If the cylinder has a lot residual fuel in it from a leaky injector, I would think the car would have a hard start issue and the fuel odor quite overwhelming once the car is started.

[Liandri]

Good luck. I tried diagnosing this a couple years back to no avail. For me it only happened at cold start idle and went away immediately after it was done sputtering. Stock tune. I tried coils and plugs but it felt like some sort of software bug to me, only doing a battery reset would change the behaviour. After flashing to MHD, it never returned. I strongly think it's not a hardware issue and wouldn't recommend changing parts. My car had 20k and was 2.5 years old at the time. I went as far to live graph data from a snapon scanner of the event but could not capture it, the ECU did not seem aware of it. There are long running threads here and on f30post about it iirc

[rtl32]

Originally Posted by XutvJet

I only had to disconnect the MAF one time ever to remedy the issue.

The injectors in these cars should last 150K+ miles and aren't the unreliable units like those used in the N54 cars. However, things happen and parts can fail. I just find odd that you had the same exact cold start issue (no issues with hot starts) as myself as a number of people on this form, the M2 forum, and the 3/4 series forum. I believe all reported cases were remedied with time (people just let it work itself out), they disconnected the MAF, and a minority threw a number of parts at it like MAFs, coil packs, spark plugs, and/or the HPFP. You're the first I heard that's swapped injectors.

Interesting, I tried the MAF sensor within a thousand or two miles after I bought the car (disconnected, then cleaned a few times, then replaced after that) which only ever gave temporary relief. It would come and go with no rhyme or rhythm like you said. I would be happy it was starting nicely and then it would be back all the sudden.

I have also replaced coils, plugs, and upgraded my HPFP (all for tuning/maintenance not problem chasing) since I first got the car and none of those solved the issue until swapping the injectors.

Originally Posted by XutvJet

Did you determine that an injector was really leaking or just assumed it was since the issue didn't reappear after the replacement? I find it odd that a leaky injector would be the culprit because on a stone cold start, a ton of fuel is being injected and it's already super rich. It wouldn't explain why the car starts just fine and then momentarily almost stalls. If the cylinder has a lot residual fuel in it from a leaky injector, I would think the car would have a hard start issue and the fuel odor quite overwhelming once the car is started.

I figured the mechanism behind this cold start issue was the car CRANKING for fuel because rail pressure is low on first crank (from injector that leaked out pressure), it all the sudden catching up when the rail was filled back up (similar to when you hammer closed a water valve, a shock gets sent up the system), and then compensating for the sudden pressure increase by trying to lower the pressure hence causing the dip. This is just speculation, I actually never looked at the cold start fuel pressure logs more than to just make sure there was a general presence of fuel pressure.

I did not definitively test the injectors specifically when they were pulled but about 4-700 miles before the swap the car introduced a constant low load misfire/stumble that would go away when load was increased (signaling to me that injectors were having trouble until fuel pressure increased) and an off kilter idle. Since I tuned the car it has had an occasional high RPM WOT backfire type misfire at 6500+ or when anti-lagging below 4k (not HPFP psi related, that is rock solid since upgrade unless I go over e50). Since I've owned it, it's had the nasty cold starts sporadically. All three of these issues were completely resolved immediately after all 6 injectors being swapped, with no return of symptoms in over 1500 miles now.

Maybe I am one off, it doesn't sound like anyone else has had the low load misfires attributable to injectors, the knee jerk is always plugs and coils, but I keep those fresh so my next step was injectors. Glad I did them. Good luck with your builds.

Ryan