Findings and conclutions about misfires and ignition pulls

135boost

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Hi

I started this cause there seems to be numerous different approach about this stupid and very annoying issue of n54 misfires

I think half of those is just related to worn out parts like stock coil, plugs, faulty injector or just clogged intake runner, piston ring land, or something else very obvious.
But then there seems to be a bunch of misfire issues not covered by those common easy fix and owners has throwed and swapped every part in whole engine department and still struggle with this issue.

First this engine is still just a petrol burner, air, fuel, squeez, bang, exhaust dump..
I have struggled with these for few years now and still miss the root cause for them. Trebila has been awesome help and p33p33 even more awesome help to tune this but still there is to much on the dark side of this issue, and for sure, i'm not the only one with this. This seems to be stupidly sensitive to all what can cause misfires.

At the end of day, solutions should not be in a level of "edge where maybe it ignite every pulse", more like enough room for to be sure we aren't even close to misfires, damn, gtr's with these miniatyre plugs iginite even with 55psi and 2000 horsepower and propably 40% more cylinder pressure at the moment of ignition without issues.

What i have read from these forums, numerous injector swaps, numerous playing with different coil packs, spark gap, finetuning of software, different plugs, wichcraft, gremlings, different brand of fuels etc and still misfires even with big players like Tony @ vtt, Terry @ burgertuning and numerous others too.

Damn it, even 1970 made carburator engine turbocharged ignite mixture without issues so why is this so damn difficult.

First known real issue, miniatyre size spark plugs what for sure is more prone to run to issues cause of very thin layer of insulator and frame been close to electrode, that is somethinw what just is, caused on limited space in combustion chamber in di engines.

Then few things about di and plug relation what can trig issues, injector is very close to spark plug and with very high horsepower n54, on di, when injection window start (not sure about excact timing cause of missing map in xdf but some guess is that window is some 250 degree ) piston is close to tdc and maybe there is on big injection quantitys in that situation to some degree of risk to wet the plug.

First question, have there been any notices of difference in full di to the max with bigger di hfpf systems versus di plus pi cause on that occation, di plus pi should be less prone to this if that is the case

Second question, b58 style spark plug with much more protected center electrode could also provide some protection against that wet foul possibilities, some notices if that does any positive effect against misfires. Someone maybe even tryed pi only?

Seems that pr coils, b58 coils etc has for sure enough energy to ignite this kind of combustion so i think we all can be sure it's nothing to do with pure spark energy. Energy need is also reduced with spark gap reducing even if combustion pressure increase energy need and spark resistance at level of 1 to 1

What about mosfets or cabling to coils, i don't think cabling are too small to proper support coil charge even if they ain't ment to support more than stock coils but what about mosfets ability to disspatch heat with much longer dwell times in optimated dwell maps? I really think we have enough knowledge on those proper optimum coil dwell tables to rule out thatwrong chargetimes from issue causings list.

There has been one test what i have found from web where those was measured and conclution was that b58 coil is superior to allmost everything what can be throwed in in dumb coil markets. Has there been any taughts on temperature issue or is there real differences when used smart r8 coils on misfire front?

What about heat sink glued with thermal glue on top of all mosfets? Not so very difficult task to do.

On mechanical side there has been reported that some teflon tape wrap to injector has cured a small amount of misfire issues, sounds like bush fix, it may work but not caused of better sealing to combustion, it should worse out that sealing situation caused by many time bigger area to be sealed than that orginal 8mm but there is one thing what on my opinion has been totally missed and what that teflon tape could on short term cure.

What if the issue on that is not gas leakage, but jiggering of whole injector as a result of combustion chamber high pressure pulses?

Seems to be that issue is escalating with boost pressures over 25 psi and that teflon wrap fix has been when there has been complains about injector bore been out of shape or loose.

I came to stupid taught, what if that big cylinder pressure is starting to resonate the whole injector against the injector holding clip, that could easily explain wear out injector hole, that for sure could cause very erratic injector behavings caused on movements inside of injector and it's needle. Area of injector is in size of 0.5cm2 (8mm cross section ) at injector injecton nose where that teflon seal sits so if there is some 100bar cylinder pressure at highest point, the spring has to be hold some 50kg force and i'm sure it does not withstand that without some warping or small resonation. What if the injector locking spring is orginally designed to work as some kind of hydrolock protector to give up after example double orginal cylinder pressure and designed to protect pistons and stock rods in a case of injector fairlure and pump combustion chamber full of gasoline? And then when we reach that level with double absolute charge pressure, what is in a level of prox 40psi compared to stock some 20psi abs, 14,7psi plus some 7 or 8 psi boost? Just playing with idea...like valve float, difficult to show out as small amount until it's sewere issue an can be heard.

On these n54, that resonating frequency is in a rateof 2500 to 4000hz, half of engine rpm so monitoring should on my opinion be done with high speed videocamera in a dyno under full pulls to se if there is a issue. That spring type injector holder is not to be seen in any diesels, tfsi, n55, b58 or other engine models so what if this is the real issue in these n54's and was at the beginning a idea of bmw engineers to do it as that mentioned protector cause it was their first di engine?
I think movement level to mesh up injector is in a level of 1mm or something so movement does not have to be even visible to eye without slow motion diagnostic video.

Easy fix for sure is stack 2 springs to clamp that injectors, doubling it's clamping force. Has anyone even tryed that?
I have a spare of those and for sure will throw them in to do road test to it but i don't have easy access to chassis dyno or high speed camera equipments to do real investigatios other than road tests.

On afr side to solve this issue, it seems to be regardless of afr, for sure very rich mixture is causing misfires but even of correct best power level afr or little on lean side of it, it seems to be a issue still having mystery misfires.

Next question, if that is dme related, then all with syvecs s6 or s7 should be without any misfire issue at all, is that the situation? If it is, then dig again us in to dme mosfets.

In some occations, there seems to be claims that weak battery is causing these kind of issues but
That should stress more generator than trig misfires if dme feed voltage stays on decent level.

For sure i know this is a network of different bus in these so maybe there is some relations caused of some mystery module like lfpf but i think it's long shot.


My setup starts to run to misfires in a region of prox 23-25 psi, tested 3 different injector packs, 3 different coil packs, both pr and n58 coil packs, slight different afr's, diferent plug gaps, different dwell table values, even p33p33 knowledge, and misfire is popping up somewhere in 6000-7100rpm at every pull with at least one gear recovered after second or two to normal again and to the point of misfire everything seems to be totally normal except ignition pulls
Propably related to some torque limit table, 6at (testing at the moment on 29psi and target at the end is 33psi with 1:1 boost exhaust pressure) what i think is a totally other issue.

That ignition pulls has been reported that is more prone on xi models, and if so, it can be related to noise from dront diff ve rwd cars, more than diferent in calibrations or something else, faulty prop shaft or half shafts can bring noise to oil pan what can trig it but on mine, i tested few pulls with knock deactivated at over 3500rpm and still puls so it's not knock in my situation.

Known trigger increaser is forged internals, check, high lift cams, check, closed deck, check, xi, check, so i have them all.


Taughts?, suggestions to keep my mouth shot? Ideas ? And yes, again, i know my english is not perfect so gramma lections suggestions don't belong here eather or could it be better to write on my natives Finnish or Swedish 😛
 
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Solution
“We choose to tune bmw n54 in this insanity and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one ... so.. is it even technically possible to increase that 1389 value or is only path port injection

iminhell1

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I like your thinking. I too feel the root of the problem has not yet been found and everything out currently is just a trial run and the consumer is the beta tester. I honestly only see 2 companies testing their parts on their cars, VTT and Burger. Everyone else seems to use the public at large as a test (or they don't post about personal testing enough to make me remember they are).

The cylinder pressure and injector hold down flexing could be a real concern. I do recall a post or 2 where the person didn't get them installed the correct way and it caused problems. The hold downs do have a bit of curve to them and are only meant to go on 1 way (spring steel). But doubling the hold or increasing it at all might bring a problem of the hold down bolt and the threads in the head. Both of which probably don't have much strength beyond the current hold of the spring. If we can stud it and the threads can go deeper, may alleviate some of that risk.

And I know you're onto something just by looking at the difference between early and late injectors. Early injectors have a narrow shaft while later are larger. Many thought this was because BWM put more coolant in the later. But I've never bought into that. My thought was it was a design to hold the injector tighter. And like you say, it's rattling in the bore. I've never seen witness marks on mine, but maybe I wasn't looking close enough either. I do know that I don't have carbon above the seals; and I'm amazed that little Teflon seal works as well as it does.

But the plug wetting is a real thing IMO. These cars do just fine lean, or lean by PI standards. We really can't use fuel to cool like you can with PI. Our DI only AFR target is really mid/low 12's and at most high 11's. Any more and it's almost guaranteed you see timing pulls and misfires. The assumption there for most was a lean misfire and it needs more fuel or it's pressure crashing. Neither of which I feel are generally the case. These cars just need to run leaner than most feel is comfortable. It's the nature of DI and it's efficacy.
 

135boost

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Seems that we have similair toughts so it's nice that i'm not alone with my ideas.

That is known point that di should run a bit leaner than pi, prox a 0.5 point afr and that is something i targeting at.

About the bolt and it's ability to withstand that double force of 2 springs, i will swap it to 12.9 stud to get all out of that thread and if that is not enough, i'll put thread insert there but as oem, there is for sure room for heavier spring cause of the way it's torqued down, the sequence is that the bolt first has enough force to pull that spring down to head surface level and then some degree more force to secure it and that seems to happend with ridiculous low 13nm force so to overcome spring force, that is overcomed by some 7nm tightening torque.
Bolt it selves is 7x20 and nominal max tightening torque on even 8.8grade 7mm is at the level of some 20nm so with max out aluminium head thread lenght, and with 10.9 or 12.9 class stud it should be doable to double out spring rate. 8x35 stud at grade 12.9 is then withstand some plus 40nm torque so it sounds close to overkill in this but it's more than super easy to find at least here in europa.

One thing what have been overlooked here on my opinion is those broken injector retainer springs and injector blow outs what is to be found in web, resonance is for sure increase load of that spring versus if it is kept static and cylinder pressures on decent levels, cylinder pressure it selves does not increase stress factor before injector starts to resonate.

Then one thing about injector gasket and that aluminium shield what to remove before install, as Tony from vtt tolds, he has been installing numerous time injectors with old seal without issues,

My professionality is to do with hydraulics, and as coarse education how hydraulic seals work, it's not that tight fit that do the sealing, it's more tight enough to be sealed before pressure from one side start to squeez the seal. Squeezing has a effect to narrow the seal looked from pressure direction and that seal material is expand then against it's bore or cylinder where it sits.

Injector seal is still all most acting there the same way, it will give up if there is even a small leak before that squeezing effect take place, gas or liquid escape from very small hole at high pressure superheat that escape jet temperature and for sure burn a space for it to escape more, then resonance for sure is eating it up gaskets why there can be reported misfire issue dissapear after injector seal repair. At the end, it may be all just masking real issue, warp and resonance of the spring.

One other taught about odd issues if there is that spring resonating and injector movements, frequency of it is same as ignition pulses so maybe even knock sensors hear it and cause sounds what is been monitored as knock, there we have possible reason for ignition pulls too.

This all is still on level "what if" before someone has possibility to do some high speed video of it to see how injectors behave in extreme pressure situations
 
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wheela

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These misfires occur on n55 too. That platform also AFR's higher to avoid misfires. I've never understood why DI would bw that way, and everybody just seems to take for granted "that's just the way DI is", which never sat right with me. However, I saw somewhere somebody runnuing a stage 3 turbo (speedtech I think it was?) on n55, and their AFR's were in the 10's up top, which I hadn't seen before. Since this was stage 3 with free-er flowing exaust path through the manifold and turbine housing, the thought occurred to me that the misfires may be related to the high back pressure when pushing stock or hybrid turbos hard. My theory is that the misfires could be due to excessive combustion byproducts (CO2) left over in the cylinder after the exhaust cycle. So then in the next cycle, even with a good ratio if O2 to fuel, there are still so many CO2 molecules present between the fuel and O2 charge that it makes that difficult to ignite rich mixture that much more difficult to ignite - to the point where you're right on the edge of getting random misfires, and leaning up the mixture pushes you just far enough away from that point to resolve the issue. So I suspect the problem isn't so much due to DI, but more due to the restrictive exhaust path through the head, manifold, and turbo housing that BMW gave us in an attempt to keep extremely good turbo response at stock power levels. Most people running hybrid turbos on these platforms doesn't do much to alleviate the very high back pressure present at the exhaust valves. Anybody have any experience using stage 3 turbos and being able to run lower AFR's to give some credence to this theory?
 

135boost

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Hi ..and nice to see more replys to this.

First, i had small gap in my knowledge, seems that n55 too have some kind of spring related to injection, much studier than n54 and hidden under that cover plate and i'm not sure how that work in real life, never seen one, but that is nothing to do with n54 issues.

About DI running leaner than PI, there is one major diference what on my opinion coud explain it to some degree.
On pi, whole charge cycle is fueled and in a situation with overlap, there is fuel escaping trough open intake and open exhaust valve forward to primary runners in exhaust manifold, that eccessive fuel for sure has capable to burn in exhaust manifold and turbine housing before it reach lambda probe. That eccesive burnt fuel is measured too in afr monitoring and al what has escaped must be compensated with more fuel injected to intake. On DI engine escaping phase is only air cause injection phase can start after exhaust valve is closed. Summarum, combustion chamber has same afr when ignited but that eccessive clean air monitored by lambda probe show it leaner.

On these n54:s, misfires occurs at the same rate even if there is huge single turbo or even bigger, big not hybrid twins like mine(g25-660) with charge/exhaust pressure under 1:1ratio trough whole rpm range, in my engine all way to 8000rpm.
Misfires start at some 25psi and some 5000 plus rpm on wot and there is the situation where especially on big turbos is true max torque and therefore max cylinder peak pressure

To reduce flow restrictions i have
- over 235/170 [email protected] head with big valves
- schricks high lifts
- those huge turbos with .71 ar housings
- 3 inch dp
- 2x3 inch middle pipes
- 3.5 inch rear section

I really don't think this is exhaust restriction.
 
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135boost

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I have stock deck height and head surface, not any clue how that could on technical side trig that misfire.
I Have cp low comp pistons at 9.2:1, cometic headgasket and 2 step colder ngk's at the moment but next step is to try those more protected n58 plugs.
 

RuskiRacer

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I was just asking more for something to rule out ofthe equation. Are you sure you may never have bent a valve possibly with the shrink high lifts?
 

RuskiRacer

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Also did you fix this whole injector bracket situation? Have seen it cause missfires on customers cars when its loose or damaged
 

135boost

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I checked valve to piston clearance when i build this engine and yes,
Stock pistons does not have enoug space for high lifts but these cp's does.
Compression is ok, no pressure leaks so i think that bent valve is also ruled out.

I don't have damaged injector bracket, next test to avoid those misfires is with double
Bracket and maybe 8mm stud.
That is to be done next week

Other test is to be done with those b58 plugs, ngk 95248 where center electrode is much more
protected, my 2 cents is that is some evolution to protect plug in a DI engine against wet fouling.
This is too to be done next week.
 

iminhell1

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Far as plugs.
Stock there was an area on the piston fuel was supposed to hit and bounce up and further disperse. We add more cylinder pressure, more fuel volume (and injector open longer) and earlier ignition timing relative. The way the fuel bounces and disperses is going to change drastically. Just changing a plug design isn't going to be the cure all here. I personally think the aftermarket piston is a real factor here. I highly doubt they did any CFD for Di and fuel dispersion. Why would they.

Rather than change plugs, index them. Using the ground strap to block the fuel should achieve the same result, or prove they are not the problem. Strap should point away from the injector; if we're assuming it's the primary firing of the injector wetting the plug. If it's the reflection wetting the plug, face the strap to the injector.
And if that is actually the case, wetting from either or both situations, then maybe there was more to the factory plugs than people assumed ....

I just don't feel Di being treated as PFi is what should be done, both by us self engineers and professional parts production. It's an animal that has very specific part requirements.
 
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135boost

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Far as plugs.
Stock there was an area on the piston fuel was supposed to hit and bounce up and further disperse. We add more cylinder pressure, more fuel volume (and injector open longer) and earlier ignition timing relative. The way the fuel bounces and disperses is going to change drastically. Just changing a plug design isn't going to be the cure all here. I personally think the aftermarket piston is a real factor here. I highly doubt they did any CFD for Di and fuel dispersion. Why would they.

Rather than change plugs, index them. Using the ground strap to block the fuel should achieve the same result, or prove they are not the problem. Strap should point away from the injector; if we're assuming it's the primary firing of the injector wetting the plug. If it's the reflection wetting the plug, face the strap to the injector.
And if that is actually the case, wetting from either or both situations, then maybe there was more to the factory plugs than people assumed ....

I just don't feel Di being treated as PFi is what should be done, both by us self engineers and professional parts production. It's an animal that has very specific part requirements.
there could be part of truth in this spray bounching from piston top too but on my opinion and tests of spray patter from injector it does support this theory, it does not spray fuel at direction of piston, there is 4 small hole in injector and they spray almost horizontal, maybe some 20-30 degree max from horizontal. for sure piston is doing it`s own mixing but most of air fuel mix is not bounching from piston. i did even slow motion video of spray pattern.
 

135boost

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Little more speculations to misfires, sorry not to have time yet to test if those injector brackets do any difference, got b58 plugs today so hopefully tomorrow i been little closer to solution.

That second pic is showing quite close to one possible issue and what b58 (colder ones, 95248) could do against wer fouling.

Then one thing what irritate me quite much, there is nowhere to be found tables where is to be seen where injector phase start and where it stops, only estimation about prox 250 degree window.

Injection phase should end prox 35-40 degree before ignition and now when we tune these, is tune with huge amount of fuel increase timing of injector too, for sure these behave very different than pi injectors, where fuel pressure is static and injector is open or close. These can do multiple injections being some 10 times faster than pi solenoids, then they can manage to adjust injection quntity with curent values, third is to adjust fuel press from 800 psi to 3500 psi so for sure, there is variables enough.

So, who find that injection window, ve table, and all other strange tables what can cause misfires and explain it tu us.

My 2 cents
 

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carabuser

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No time at the moment but I can point you to a good starting place.

Page 648 of the BMW FR details the creation of the SOI and EOI parameters
Page 2122 of the Continental FR details how those signals are corrected

Chapter 7 of the Continental FR gives you a complete overview of the injection process.

I think the injectors work in 3 pulses so it's not as simple as just having a SOI and EOI setting. There's a distribution factor that's used to determine how much of the total fuel mass is injected at each pulse.

I've only looked at the tables that are different between ROM versions. The distribution factors change on the INA0S "is" tunes.
 
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wheela

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So
No time at the moment but I can point you to a good starting place.

Page 648 of the BMW FR details the creation of the SOI and EOI parameters
Page 2122 of the Continental FR details how those signals are corrected

Chapter 7 of the Continental FR gives you a complete overview of the injection process.

I think the injectors work in 3 pulses so it's not as simple as just having a SOI and EOI setting. There's a distribution factor that's used to determine how much of the total fuel mass is injected at each pulse.

I've only looked at the tables that are different between ROM versions. The distribution factors change on the INA0S "is" tunes.
Thanks for sharing this. Sorry if this is a dumb question, but what are the BMW FR and Continental FR, or any clues how a person could find these? I'm sure FR stands for something, but no idea what. Googling these (not suprisingly) yields french BMW sites, and continental tires lol. I'm always interested in learning and these sound like good technical resources :)
 

carabuser

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FR is shorthand for funktionsrahmen. Just a function description of the DME code. They take all the guesswork out of table definitions but they can be hard to read as they aren't intended for an end user, rather just as technical documentation and reference for calibration engineers.

They have been posted a few times on this forum. I don't have a copy to hand as I'm away from my PC but you might be able to find them elsewhere on this forum by searching for MSD81 funktionsrahmen.
 

wheela

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FR is shorthand for funktionsrahmen. Just a function description of the DME code. They take all the guesswork out of table definitions but they can be hard to read as they aren't intended for an end user, rather just as technical documentation and reference for calibration engineers.

They have been posted a few times on this forum. I don't have a copy to hand as I'm away from my PC but you might be able to find them elsewhere on this forum by searching for MSD81 funktionsrahmen.
Thanks alot, I'd never have come up with funktionsrahmen! I'm 9e60b n55, so I'll poke around 1726 funktionsrahmen and see if I can find anything for my DME.
 

135boost

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For sure they are very difficult to read caused of some 13 000 pages long pdf where half of pages is german language.

Then to hardware,About b58 plugs installed those yeaterday, no issues, few pulls but only to 5000rpm cause of traffic.

Then those injector springs, installed those too and did some calculations of spring force and bolt stress.

Tension of that spring is prox 7 kg/mm and it's pressed to some 7mm so spring force is in level of 50kg
But to calc bolt stress there is 50kg of force from spring preload and additional est 50kg force from cylinder pressure
So static load isat least 100 kg and if there is some resonanxe in injector, every mm increase that stress by 7kg.

Now with double spring, 1 have 100kg spring loat plus 50kg pressure load and no flex so calc is that load increase is not double, closer to 30%