2014 BMW F30 -N13 - Engine misfire

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chad66
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2014 BMW F30 -N13 - Engine misfire

Post by chad66 »

Hi Guys,

New to the forum and am a new user also of the PICO Scope, Well actually my scope is on its way to me and cant wait for it to get here. Been newly introduced to labscopes by a friend who uses Pico at a dealership and was amazed with the indepth details.Anyway, am currently crying my eyes out on a BMW F30 N13 engine with a consisted, well actually it will sometimes run perfectly smooth but constant cylinder 2 misfire keeps appearing.

My Friend did come in to do a check with my current existing scope (A Hantek) and found an unusual negative vacum on a cylinder when the misfire occurred. However, was not able to quite figure out the cause.

Work so far done was
Cylinder head removed and valves faced and seats too. coils swapped and plugs too, Valvetronic motor swapped from a know good car, Intake Vanos swapped from a know good car, injectors tested at Bosch Service Centre.

Did a Differential pressure test on the inatake (vent valve port) and also the dipstick sleeve (which showed even differential pressure/Vacum.

Unfortunately my friend is not around to assist so im at a dead end at the moment. Would appreciate if someone coulod suggest which direction to take or what tests to conduct to narrow down the issue.

Thanks in advance.

Iver
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by Iver »

You started with a misfire and did all that work and still have a misfire. Is that correct?


On that engine I would be thinking MOSFET

chad66
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by chad66 »

Even swapped DME, so im guessing Mosfet not the problem

chad66
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by chad66 »

Hello Everyone,

Finally have my Picoscope in and first thing I did was take an in cylinder waveform for the concerned vehicle. If someone could shed some light on the interpretation of the waveform would be much appreictaed. attached is the waveform
Attachments
BMW 316 cyl 2 in cyl pressure.psdata
(16.71 MiB) Downloaded 230 times

Steve Smith
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by Steve Smith »

Hello and thank you for the post.

It looks like you have captured the proof you need to confirm this is a mechanical/valve train control issue
Image 1
Image 1
As you can see in the image above we have a momentary loss of compression because of the inlet valve failing to open sufficiently to generate compression

Note the uneven intake and expansion pockets along with the "dish" type intake pocket with poorly defined open/close events

Given you have re-seated the valves we have to assume the cylinder head and valve sealing is fine

With this style of engine the valve train can be controlled conventionally where intake air is controlled by the throttle and valve lift is fixed, or, the the throttle is held open and air intake is controlled purely by variable valve lift.

Could we prevent variable valve lift operation and run the engine conventionally, i.e. using the throttle only to control air flow?

If this cures our sporadic misfire then we can attribute this misfire to variable valve lift or the control there of.

You can determine how the valve train is being controlled by monitoring manifold pressure.

The following forum post will assist you here. topic21932.html

I hope this helps, take care......Steve

Iver
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by Iver »

Sticky Valve, sporadically not opening ??

Additional Pressure sensors on exhaust and inlet will tell you which.


Steve Smith
Could we prevent variable valve lift operation and run the engine conventionally, i.e. using the throttle only to control air flow?
I would agree other than the fact that Chad is suggesting a SINGLE CYLINDER misfire ?

Valvetronic (Variable valve lift) for sure would affect all cylinders.


Indeed when the low Compression event occurs it is preceded by more vacuum/ less pressure - it is gasping for air !!!???

Could this be a (Intermittently) failing Hydraulic Lifter ??
Last edited by Iver on Mon Aug 10, 2020 12:05 pm, edited 3 times in total.

chad66
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by chad66 »

Thank you so much guys for the very informative insight... To additionally add to the diagnostics, I have disconnected the valve tronics motor and am attaching waqveforms for the suspect cyl (Cyl 2) with valvetronics disconnected (As i understand, correct me if wrong, once valvetronics is disconneted ECM holds the valve open at max lenght). Also attached is a waveform from cyl 1 (with valvetronics connected). Im trying to ascertain what is causing the intake valve to not open or is there some restriction somehwere or something i dont see as im really new to this labscope testing but must say its truly very interesting.

Once again Thank you guys for the support.

Iver
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by Iver »

Chad

I edited my last post so you may not have seen the additions I made.

Think about this then prove or disprove !

I would agree other than the fact that Chad is suggesting a SINGLE CYLINDER misfire ?

Valvetronic (Variable valve lift) for sure would affect all cylinders.


Indeed when the low Compression event occurs it is preceded by more vacuum/ less pressure - it is gasping for air !!!???

Could this be a (Intermittently) failing Hydraulic Lifter ??

chad66
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by chad66 »

Hi Iver,

Thanks for the input, was wondering though when i have the valve tronics disconneted dont have the misfire. If it were a failing Lifter I should see the problem come up even if its intermittent. What do you think ?

Iver
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Re: 2014 BMW F30 -N13 - Engine misfire

Post by Iver »

Hi Chad
was wondering though when i have the valve tronics disconneted dont have the misfire.
I have some understanding of this engine & Valvetronic did mess with my metal health when we first saw it.

I cannot tell you how Paralysing Valvetronic fault could ever solve a SINGLE CYLINDER Misfire. My knowledge is that Valvetronic alters the Inlet Valve Lift Equally across all cylinders on that bank.
If it were a failing Lifter I should see the problem come up even if its intermittent.
I'm not sure what you mean !
Intermittent or Permanent, how would you see a failed lifter. Of course, Pressure testing & Diagnostic elimination may guide you to suspect the lifter.

I'm not so sure how you could non intrusively test a Lifter. If you remove it then it may be obviously faulty or not.

My only thoughts are a pressure transducer on an Oil Gallery somewhere - Would be interesting to see that !

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