[MSport_Jon]

So I have a 2015 F25 X3 with N55 engine with some annoying misfires that at times, are flat-out embarrassing. I decided to finally try to get rid of the issue I 've been having for a long time and not fixed due to lack of error codes and mechanics not willing to troubleshoot car without trouble codes.
For a while, I have been experiencing misfires at startup but only when the engine is up to temperature.
In the morning when completely cold the engine will start fine the way it is supposed to. But once the engine is warm when I start up the engine I get misfires for about 10 - 20 seconds and little by little the car recovers.
Say I went to the mall and spend an hour or two there. When I come back and start up the engine… Misfires for about 10 – 20 seconds. The only way to make it go away immediately is either to place it in drive or turn the steering wheel. It weird.
So after 80k kilometers, I decided to change spark plugs, coils, and injectors.
Changing the injectors is a tremendous pain in the ass especially with the new style fuel rail. The fuel rail is the biggest problem. The rail is connected to the injectors and is not individually removable as there not individual screw fittings at the rail. So you have to remove all six to get just to one. Not like the old n54 or first-run style n55. Consider getting the old that allows for quick individual injector change if you are at this stage or will be at this stage at some point.

Make sure you buy a quality tool to remove the injector or you will regret it if you don’t.

You will have to remove the strut brace on the passenger side and the cowl undertray. Then you will have enough space to work.

Make sure you check everything because the way this car is built, you can’t turn the car on a test on unless you put everything back and if have a problem, you will have to go back again and remove everything to get to the 6th cylinder if that is in fact where the problem is.

I wanted to take pictures but boy is this job frustrating as hell.

Tools that you will need are:

Torx buts,
Sockets
Extensions
Inverted Torx sockets
An injector well reamer/cleaner kit… do not skip on this… if there is rust down there, you will not have a good seal.
BMW n55 injector removal tool
Wrenches for the tool. In my case, I needed a 24 and a 19 wrench size
Flared wrenches for the injector lines.
Patience and knowledge. YouTube is your friend here.
Good luck PM if you have questions.


I will report back once i am done with this....

[MSport_Jon]

Didn't work. Still have the warm start misfires.

It's looking now like it is the HPFP. I can finally manually produce the noise by activating the pump in ISTAwhen warm. Sounds like something is grinding in there.

[e30lover318i]

Are you saying your having a misfire with no check engine light ?

[najnad]

I had a misfire with no check engine light...was a bad spark plug...

[e30lover318i]

Interesting I’d like to know how a car with MS43 is more sensitive to misfires than a car 20 years newer

[ga9213]

Are you able to see what IAT sensor readings are on warm start? Cleaned the MAF?

[6MT_Addict]

Firstly did you pull codes? Even with no CEL there may be shadow codes. As soon as a misfire is detected the engine will log a code, but if the ECU can smooth it out then it likely won't trigger a CEL. Even if there are no codes there's still data logs that can be pulled, or a reader connected to actively log values during the fault if the data is insufficient.

1. Did you code the new injectors? If not, that's likely causing or contributing to the new misfires.


2. Check your intake ducting for leaks (visual and/or smoke test) and clean your MAF sensor. After replacing my spark plugs I had missing and super rough idle at startup that turned out to be because the gasket at the downstream side of the filter box was folder over allowing air to get sucked in that the MAF wasn't reading.

Check everything from the filter box to intake valves. If you've removed the intake manifold without replacing those seals that can allow air in or your charge pipe might be cracked.


3. Run a diagnostic on the fuel pressure at the rail. ISTA can do this I believe.

Also take it to another shop unless you want to DIY. A mechanic who won't diagnose a misfire because there is no CEL is a lazy or inexperienced mechanic. As I mentioned above even a basic OBDII dongle to Carly or other apps can log information that would help pinpoint the issue.

[MSport_Jon]

Originally Posted by 6MT_Addict

Firstly did you pull codes? Even with no CEL there may be shadow codes. As soon as a misfire is detected the engine will log a code, but if the ECU can smooth it out then it likely won't trigger a CEL. Even if there are no codes there's still data logs that can be pulled, or a reader connected to actively log values during the fault if the data is insufficient.

1. Did you code the new injectors? If not, that's likely causing or contributing to the new misfires.


2. Check your intake ducting for leaks (visual and/or smoke test) and clean your MAF sensor. After replacing my spark plugs I had missing and super rough idle at startup that turned out to be because the gasket at the downstream side of the filter box was folder over allowing air to get sucked in that the MAF wasn't reading.

Check everything from the filter box to intake valves. If you've removed the intake manifold without replacing those seals that can allow air in or your charge pipe might be cracked.


3. Run a diagnostic on the fuel pressure at the rail. ISTA can do this I believe.

Also take it to another shop unless you want to DIY. A mechanic who won't diagnose a misfire because there is no CEL is a lazy or inexperienced mechanic. As I mentioned above even a basic OBDII dongle to Carly or other apps can log information that would help pinpoint the issue.

This car started doing this after a year of owning it. Ordered the car from BMW and i have been the only owner.

No one will touch this car if it doesn't produce a code. Taken the car multiple times to BMW for diagnostics and short of calling me crazy they say that it is normal.

This problem only occurs when the car is warm. When it is cold, it cranks perfectly.

I have done the following;

Cleaned sensors, two pressure sensors and one MAF. Same problem however transmission now shifts more smoothly after doing this.

Checked intake joints for loose clamps. Seems ok but haven't smoked it. Same problem

Change the spark plugs coils and injectors. Same problem.

Tested the fuel rail using ISTA and seems ok. it seems to hold the pressure fine.

Oddly initiated the HPFP with ISTA while the car was off and i could hear that metallic screech sound that i hear along with the misfires. I leaning towards the HPFP now since I discovered this.

every time i do this procedure i can hear the sound although not in the same length or intervals but the same sound nonetheless.

[najnad]

how many miles on the engine? Have you replaced the vanos solenoids?

[6MT_Addict]

Originally Posted by MSport_Jon

This car started doing this after a year of owning it. Ordered the car from BMW and i have been the only owner.

No one will touch this car if it doesn't produce a code. Taken the car multiple times to BMW for diagnostics and short of calling me crazy they say that it is normal.

This problem only occurs when the car is warm. When it is cold, it cranks perfectly.

I have done the following;

Cleaned sensors, two pressure sensors and one MAF. Same problem however transmission now shifts more smoothly after doing this.

Checked intake joints for loose clamps. Seems ok but haven't smoked it. Same problem

Change the spark plugs coils and injectors. Same problem.

Tested the fuel rail using ISTA and seems ok. it seems to hold the pressure fine.

Oddly initiated the HPFP with ISTA while the car was off and i could hear that metallic screech sound that i hear along with the misfires. I leaning towards the HPFP now since I discovered this.

every time i do this procedure i can hear the sound although not in the same length or intervals but the same sound nonetheless.

I wound take it to an independent BMW mechanic for diagnosis. BMW might have refused to look at it to avoid a warranty claim, but that also seems odd since BMW AG essentially pays the dealership to perform the work AFAIK.

[6MT_Addict]

Originally Posted by najnad

how many miles on the engine? Have you replaced the vanos solenoids?

+1 could be a vanos issue, they are pretty easy to check/clean. Secured to the front/top of the engine.

[one9kilo]

Originally Posted by 6MT_Addict

+1 could be a vanos issue, they are pretty easy to check/clean. Secured to the front/top of the engine.

I initially though Vanos solenoid too, but doesn't that usually throw a code?

I replaced my solenoid recently and that did solved the misfires. Doesn't hurt to try cleaning it first since it's easy to do. I did try cleaning them first but that didn't help. Had to replace them both. Be careful with what you clean it with. You don't want to damage, weaken, or stretch the little rubber o-rings.

Again, doesn't hurt to try. However, the fact that OP is getting the misfires when the car is warm rather than when it's cold makes me think it's not the solenoids. Plus, it's no throwing any codes which happens when the solenoid is stuck (won't actuate) or sticking. ISTA should identify it. This is from my experience though.

If you plan to take out of the solenoids, measure voltage and then test them to see if they actuate when powered.

I'm no expert but is seems you're on the right track if you were able to replicate this noise your heard.

[HalfAnP]

Originally Posted by MSport_Jon

Didnt work. Still have the warm start misfires.

Its looking now like it is the HPFP. I can finally manually produce the noise by activating the pump in ISTA. sounds like something is grinding in there.

My F25 was doing this too. Not just misfiring but also "hunting" at idle when started (worse when cold). I just replaced the HPFP two days ago, now the problem is gone.

No codes either, not until the HPFP finally failed for good. For reference this is an early-ish 2011 F25 with the continental pump.

[FranzX3M]

I had similar issue, especially when cold. Would start but sputter and even stall. Threw all kinds of codes. Replaced the battery. All good.

[MSport_Jon]

Originally Posted by e30lover318i

Interesting I’d like to know how a car with MS43 is more sensitive to misfires than a car 20 years newer

I honestly think BMW does this on purpose to avoid customers taking in their cars every time there is a misfire that can be controlled or mitigated.

[MSport_Jon]

Originally Posted by 6MT_Addict

I wound take it to an independent BMW mechanic for diagnosis. BMW might have refused to look at it to avoid a warranty claim, but that also seems odd since BMW AG essentially pays the dealership to perform the work AFAIK.

Tried doing that. Took it to Motorsport Moritz in Wackersdorf Germany. Flo (Owner) test drove it and check it, but again, most mechanics need a trouble code to start somewhere.

[MSport_Jon]

Originally Posted by ga9213

Are you able to see what IAT sensor readings are on warm start? Cleaned the MAF?

Cleaned MAF a month or 2 before this job. Still misfiring when warm.

[MSport_Jon]

Originally Posted by one9kilo

I initially though Vanos solenoid too, but doesn't that usually throw a code?

I replaced my solenoid recently and that did solved the misfires. Doesn't hurt to try cleaning it first since it's easy to do. I did try cleaning them first but that didn't help. Had to replace them both. Be careful with what you clean it with. You don't want to damage, weaken, or stretch the little rubber o-rings.

Again, doesn't hurt to try. However, the fact that OP is getting the misfires when the car is warm rather than when it's cold makes me think it's not the solenoids. Plus, it's no throwing any codes which happens when the solenoid is stuck (won't actuate) or sticking. ISTA should identify it. This is from my experience though.

If you plan to take out of the solenoids, measure voltage and then test them to see if they actuate when powered.

I'm no expert but is seems you're on the right track if you were able to replicate this noise your heard.

When you say "selenoids" you mean VANOS, right?

I think it might be the HPFP at this point but I would def clean the VANOS Selenoids to see if there is an improvement at least. Car now has 85K KM's

[Weslsew]

this really sounds like an injector. when an injector doesn't seal all the way and you turn the car off, it will leak out fuel into the cylinder, causing a misfire for a few seconds at warm startup. if you let the car sit for a while until cool, it won't do it because the fuel has time to evaporate.

you said you replaced all injectors, did you use rebuilt or new? did you code the new ones with ISTA?

if you have bimmerlink, it actually has a misfire counter for each cylinder that you can watch, and see exactly which cylinder or cylinders are misfiring.

[MSport_Jon]

Originally Posted by Weslsew

this really sounds like an injector. when an injector doesn't seal all the way and you turn the car off, it will leak out fuel into the cylinder, causing a misfire for a few seconds at warm startup. if you let the car sit for a while until cool, it won't do it because the fuel has time to evaporate.

you said you replaced all injectors, did you use rebuilt or new? did you code the new ones with ISTA?

if you have bimmerlink, it actually has a misfire counter for each cylinder that you can watch, and see exactly which cylinder or cylinders are misfiring.

Yes sir. Followed the TIS procedure on how to input the flow code on the car... I think it's the pump. When the misfires are happening there is another sound that can be hard from the cabin. It is metallic in nature. I can produce this sound when i actuate the hpfp functions with ista.

[383vett]

You've been fighting this since last October. Hope you get it figured out.

[MSport_Jon]

UPDATE:

Another discovery. So when the car decides to do a fuel prime upon unlock, the car cranks fine. Granted, the engine is not super hot but it is not stone-cold either. The engine is still pretty warm.

Misfires still noticeable when this prime does not happen whether it is warm or hot. I am not sure what parameters or conditions the car uses to decide when ti prime and when not.