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Thread: High RPM misfire mystery...

              
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    Question High RPM misfire mystery...

    UPDATE:

    Take a look at this post: http://www.bimmerboost.com/showthrea...323#post330323

    Camshaft rectangrings and cam bearing ledges were broken/worn.

    ======

    First a bit of background. Car ran 11.9@122mph last year October. On January 31 this year I got RB turbos. Ever since installing them the car has developed a high RPM misfire. Lowering boost to below 14psi at 6000rpm and below 13psi at 6500rpm makes it go away completely. Raising boost just 1-2psi above that makes it comes back. This is on 94 pump gas with and without meth. Below is a copy of a recent post on another forum instead of writing it all up again...I just gapped the plugs on the misfiring bank last night from 0.028" to 0.022" and it didn't help and will be doing a leakdown test...

    copied over from original thread on http://www.e90post.com/forums/showthread.php?t=544573
    ========

    So, changed the LPFP and low pressure fuel sensor and the car still misfires up top above 6k rpm on cyl 5, sometimes cyl 6 as well in addition to 5...but 5 is there always...

    At this point what I've tried to do to address this problem in the last 4 months (issue was noticed after changing turbos and upping boost past 15psi for the very first time...see my RB turbo build/journal thread and original post from beginning of Feb 2011):

    1) Changed tunes: Procede, JB4, Cobb stage 1 w/ JB+ at the min setting. Cobb stage 1 works fine, stock tune works fine, procede and jb4 also work fine unless I up boost above 6000rpm to above 13psi. Anything with boost above that above 6k rpm will trigger this misfire in bank2
    2) Carbon buildup cleaned from intake valves
    3) LPFP changed
    4) Low pressure fuel sensor changed
    5) HPFP changed under recall
    6) Plugs changed for stock Bosch
    7) Coils swapped, misfired didn't move cylinders
    8) Okada aftermarket ignition coils
    9) Injector on cylinder 5 changed for new part and coded. Old injectors were only 1 year old, all 6 replaced under warranty last year April.
    10) Compression test was done at the dealership and all 6 cylinders had equal compression test results
    11) Datalogging with different tunes shows AFR at 12.0-12.5 at 6000rpm when the misfire is triggered and timing is ramping up without any ignition dropouts
    12) AFR on bank2 goes lean after the misfire happens indicating ECU is cutting fuel out as a result of the misfire. At the time bank2 goes lean, bank1 is still down at low 12s where bank2 used to be until I let off throttle
    13) Plugs gapped from 0.028" stock to 0.022", still misfires at the same spot
    14) HKS 50003-M54XL spark plugs (3 steps colder and single electrode Laser Iridium) have a 16mm hex nut and when placed in the spark plug hole their hex head is too big and doesn't allow any space to squeeze through any socket to tighten them. I have no idea why HKS indicated that they are compatible. Only if I ground the hex part on the plug OR used a riemer to make the space around the spark plug hex head 2-3mm wider to be able to fit a socket around it..

    I've logged the fuel pressure on the low side last night and even though now the LPFP is stronger by about 10-20psi than the original LPFP that I had (have logs that show it) the misfire still happens...

    Someone mentioned worn cam lobes...this can't be true as the misfire is boost dependent...i can lower boost below 13.5psi up top and it won't misfire...if I raise it just 1psi it'll misfire ON A LONG PULL starting at below 5000rpm...if you do a pull starting at 5k rpm it won't misfire ever...in 1st and 2nd gears it won't misfire no matter where you start the pull to redline...

    Options left to consider, and need your help/thoughts:

    1) DME ignition coil driver weak, try a different DME, possibly MSD81

    2) DME ignition coil wiring has too much resistance to coil 5, check with ohm meter

    3) Valve springs/guides - check if the valve spring is bad on cyl 5 that may cause it to stick when heated??? Doubt this is the case as there would be misfires with 1psi less than where its currently misfiring AND it wouldn't be specific at any given RPM

    4) Cam lobes - very doubtful this is the case as misfire is boost dependant, doesn't happen with 1 psi less and the car runs 100% fine on Cobb stage 1 which runs lower boost up top, as well as running fine when stock

    5) Crank position sensor - i've read that if this sensor is faulty it can throw off RPM readings and cause the engine to diagnostically misfire. It'd be very strange that its faulty given the car works fine stock and with higher boost up to 6000rpm

    6) Knock sensors - DME might be tripping some kind of knock protection and triggering a misfire on its own based off info on the knock sensors. Can these we swapped around to test?

    7) Fuel pressure regulator - if its bad it may be causing fuel pressure instability under load or pressure to go down and trip the DME diagnostic?? Does this make sense??

    And here's a little incentive Click here to enlarge Anyone that guides me on the right track, other than trying HKS plugs which I've already ordered, will be issued a nice PayPal transfer of $50 to spend on your favourite drinks lol

    P.S. What's interesting after changing the LPFP is that I still notice a slight low pressure drop at the point of misfire...i'll post csv datalogs from BT a bit later...basically pressure drops from about 5700hPa (82psi) at idle to somewhere in the 4000 range as far as I remember...before changing the LPFP yesterday low pressure fuel sensor showed 4700hPa pressure at idle and fuel pressure dipping to 3800hPa (55psi)...Could it really be that the DME is tripping out seeing this sudden low pressure drop from the low pressure fuel sensor and triggering self-protective measures by means of a misfire?? Can this be tested by simply unplugging the low fuel pressure sensor?

    ======

    Someone else on n54tech mentioned this which was very interesting (http://n54tech.com/forums/showthread.php?t=12811):

    Click here to enlarge Originally Posted by ibsr335 Click here to enlarge
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    It seems like it is either spark blowout. (plugs should fix or make the gap alittle tighter and see if it still happens) or it seems like something on the exhaust side (possible a collapsed exhaust lifter). When the boost gets above a certain point more air is getting into the cyl than can get out causing the misfire. Compression will most likely be fine if it is on the exhaust side as well because all the air is getting in and since it is just cranking and not under boost it can get all the air out. When you replaced the injector did you have to use the slide hammer or pry bar to get it out? or did it come out easy? If it came out easy it is probably blowing compression out the injector hole under high boost. Since it happened with both injectors it is probably something with the head. Did the old injector have black soot stuff all the way up it or was there just soot on the tip?

    Personally I think if it were fuel related (besides the injector you replaced) it would move around or affect multiple cylinders. And since you swapped and replaced coils, replaced the plugs already but you are going to do that again for some reason. I'd say it is something mechanical. My guess would be on the exhaust side. Do I get the $50 lol
    As for the above comment I did pull the cyl 5 and cyl 6 injectors...cyl 6 I had to use pliers to pull it out while cyl 5 I pulled out with two fingers pulling from the bottom of the injector head which it seems I shouldn't have been able to do IF everything was 100%?? I also did notice some black soot on the injectors up above the tip so don't know what to think of it..

    Here's compression test results from March 29 2011, 2 months into this issue:

    Click here to enlarge
    Last edited by dzenno@PTF; 09-19-2012 at 11:51 AM.
    Click here to enlarge

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    DO NOT use the HKS plugs. At all. They will make the problem worst.
    Let me think about this and i will let you know.
    whats the difference between a ginger and a shoe.........shoes have soles

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    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
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    DO NOT use the HKS plugs. At all. They will make the problem worst.
    Let me think about this and i will let you know.
    How come? I mean I can't use them anyway but why do you say they're bad?

    Looking forward to any help anyone can provide, pretty desperate Click here to enlarge
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    How come? I mean I can't use them anyway but why do you say they're bad?

    Looking forward to any help anyone can provide, pretty desperate Click here to enlarge
    Because...many people have had misfires using them over in Japan on the 335i. There was a bunch of discussion on the HKS forum about the misfire issues.
    I looked into HKS plugs as well, but it was a no no. Try to call HKS in Japan via Skype and see what they say Click here to enlarge
    You can use One Step Colder NGK's.
    whats the difference between a ginger and a shoe.........shoes have soles

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    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
    This quote is hidden because you are ignoring this member. Show Quote
    Because...many people have had misfires using them over in Japan on the 335i. There was a bunch of discussion on the HKS forum about the misfire issues.
    I looked into HKS plugs as well, but it was a no no. Try to call HKS in Japan via Skype and see what they say Click here to enlarge
    You can use One Step Colder NGK's.
    Have you tried one step colder NGKs? Is this the NGK 5992 plug from the Mini?
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    Have you tried one step colder NGKs? Is this the NGK 5992 plug from the Mini?
    Here is an old thread:

    http://www.e90post.com/forums/showthread.php?t=352860

    You know what, let me call a few manufacturers and I could see what theyc an do.
    whats the difference between a ginger and a shoe.........shoes have soles

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    whats the difference between a ginger and a shoe.........shoes have soles

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    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
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    Why do you think this is the solution to this particular problem? Which one of them? The only one with the 12mm thread is he1it Iridium (Powersports)...have to check the rest of the specs on it..

    Keep in mind I already tried gapping stock plugs from 0.028 to 0.022 and it didn't help...
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    Why do you think this is the solution? Which one of them? The only one with the 12mm thread is he1it Iridium (Powersports)...have to check the rest of the specs on it..
    Because they have a good rep on other BMW motors. Don't see why it would change with ours.
    The NGK are $18 / each and only one step colder.
    whats the difference between a ginger and a shoe.........shoes have soles

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    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
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    Because they have a good rep on other BMW motors. Don't see why it would change with ours.
    The NGK are $18 / each and only one step colder.
    I just checked and their hex head is also 16mm so it won't fit the socket on top...whoever at bmw designed the size of the spark plug hole should be shot a few times in the head lol wtf would they make it such a tight squeeze arghhhh basically HAVE to use a 14mm hex
    Click here to enlarge

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    Ignition misfires above a certain RPM and only at certain boost? LPFP still dropping pressure before/duiring misfire event? Am I the only one here who thinks this is a DME or electrical issue? This may sound weird, but have you logged vehicle voltage during any of these pulls? I've heard of people having these kinds of problems, and they were ultimately caused by a bad battery. I kinda doubt that's the real cause here, but it's quick and easy to test, and could be a mind blowingly cheap fix.
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    I just checked and their hex head is also 16mm so it won't fit the socket on top..
    Argh.
    Let me go to the BMW dealer and get one.
    I called NGK and they can build one for us if we get enough people interested.
    Like 15-20 sets of 6.
    whats the difference between a ginger and a shoe.........shoes have soles

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Ignition misfires above a certain RPM and only at certain boost? LPFP still dropping pressure before/duiring misfire event? Am I the only one here who thinks this is a DME or electrical issue? This may sound weird, but have you logged vehicle voltage during any of these pulls? I've heard of people having these kinds of problems, and they were ultimately caused by a bad battery. I kinda doubt that's the real cause here, but it's quick and easy to test, and could be a mind blowingly cheap fix.
    Voltage drop is also a possibility.
    A very good one.
    At which point, you can just get this:

    http://www.jegs.com/p/MSD-Ignition/M...47792/10002/-1
    whats the difference between a ginger and a shoe.........shoes have soles

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    In addition to the compression check, you may want to do a leakdown test on cyl. 5 just to be safe.

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Ignition misfires above a certain RPM and only at certain boost? LPFP still dropping pressure before/duiring misfire event? Am I the only one here who thinks this is a DME or electrical issue? This may sound weird, but have you logged vehicle voltage during any of these pulls? I've heard of people having these kinds of problems, and they were ultimately caused by a bad battery. I kinda doubt that's the real cause here, but it's quick and easy to test, and could be a mind blowingly cheap fix.
    If it was the battery it wouldn't happen consistently only on cyl 5..it would affect other cylinders as well..bank1 is NEVER affected in 4 months of testing and I've done at least a 600 pulls, seriously..

    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
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    Argh.
    Let me go to the BMW dealer and get one.
    I called NGK and they can build one for us if we get enough people interested.
    Like 15-20 sets of 6.
    NGK has a plug that fits. Its NGK ILZKBR7A-8G (stock number 5992) and they're easily attainable and not expensive either. I'm reluctant trying it as enrita in Sweden, after 500 miles on them, was on these plugs when his ringland went but I really really doubt that was the issue as they are colder than stock and electrode was in tact didn't brake off and all other plugs looked great once he pulled them out.

    Click here to enlarge Originally Posted by ScrotieMcBoogerBalls Click here to enlarge
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    Voltage drop is also a possibility.
    A very good one.
    At which point, you can just get this:

    http://www.jegs.com/p/MSD-Ignition/M...47792/10002/-1
    This is direct injection. Has this been tested on any direct injection setup and does that matter? One thing you've missed is that I already have an aftermarket ignition system. The coils have been upgraded to Okada Plasma coils that have amplifiers built into them.

    Click here to enlarge Originally Posted by Eleventeen Click here to enlarge
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    In addition to the compression check, you may want to do a leakdown test on cyl. 5 just to be safe.
    Will do...tried doing one last night but did it wrong...
    Click here to enlarge

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    Definitely, given the multiple systems at play in this situation (LPFP), I do wonder if it's something as easy as the battery/charging system and not just ignition.
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    If it was the battery it wouldn't happen consistently only on cyl 5..it would affect other cylinders as well..bank1 is NEVER affected in 4 months of testing and I've done at least a 600 pulls, seriously..
    You said it has intermittently affected cyl 6 as well. Cyl 5 could be the weakest link in the chain, with the cyl 5 driver getting the short end of the stick when the coil drivers aren't getting adequate juice, and cyl 6 going when things are really dire...with electrical stuff, you really never know until you try. Again, the fact that you have a pressure drop with the fuel pump...there are too many separate systems involved in this to count out electrical. After that, I'd chase DME.
    Click here to enlarge

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Definitely, given the multiple systems at play in this situation (LPFP), I do wonder if it's something as easy as the battery/charging system and not just ignition.
    LPFP was changed 3 days ago Click here to enlarge battery is the original battery 3 years 60k miles on it...I can log battery voltage during these pulls, that's easy but I can't see how it could be battery related...spark isn't fired from the battery...its the alternator providing electricity for the sparks unless I'm wrong of course Click here to enlarge

    In any case, again, it wouldn't be ALWAYS cylinder 5 if it was the battery or the alternator...
    Click here to enlarge

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    You said it has intermittently affected cyl 6 as well. Cyl 5 could be the weakest link in the chain, with the cyl 5 driver getting the short end of the stick when the coil drivers aren't getting adequate juice, and cyl 6 going when things are really dire...with electrical stuff, you really never know until you try. Again, the fact that you have a pressure drop with the fuel pump...there are too many separate systems involved in this to count out electrical. After that, I'd chase DME.
    Yes but what you're missing is when any one of the cylinders misfires in any one of the two banks the DME will richen up the other two cylinders and cut ignition causing a mis on another or both of the other 2 cylinders as well very soon after the first one misfired...this is easy to tell as when you check codes you can see cyl 5 only code being there, and other times cyl 5 AND cyl 6...if you're fast enough to shut down the car RIGHT after you encounter the misfire and read the codes after you'll see that its always really only cyl 5

    This, by the way, was a quick DIY in analysing leaking injectors and finding out which one exactly is the leaking one in the bank Click here to enlarge ask me how I know
    Click here to enlarge

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    Alternator-->regulator-->battery-->rest of car. What I'm saying is that if the DME is getting weak voltage, which is entirely possible given that capacitance of a battery isn't that strong, and the injector and ignition drivers are going like crazy at high RPM, in the way they designed the DME circuitry, cylinder 5 and occasionally cylinder 6 could simply be getting the short end of the stick in a low voltage situation. Again, the fact that you're seeing effects in the LPFP suggests a possiblity there. And given that the DME controls that as well, it all still points to...the DME, or the juice it lives off of.
    Click here to enlarge

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Alternator-->regulator-->battery-->rest of car. What I'm saying is that if the DME is getting weak voltage, which is entirely possible given that capacitance of a battery isn't that strong, and the injector and ignition drivers are going like crazy at high RPM, in the way they designed the DME circuitry, cylinder 5 and occasionally cylinder 6 could simply be getting the short end of the stick in a low voltage situation. Again, the fact that you're seeing effects in the LPFP suggests a possiblity there. And given that the DME controls that as well, it all still points to...the DME, or the juice it lives off of.
    Ah, that's right...ok, i'll try to see if I can log battery voltages and also voltages going to the fuel injectors and coils...i already tried logging voltages on the fuel injectors and coils...will look that over again...i do seem to recall seeing that on average the cylinder 5 fuel injector voltage was the lowest of the 6...
    Click here to enlarge

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    Again, I've heard of other E9Xes with misfire problems being solved by bad batteries...the car does seem really, really sensitive to voltage. With the amount of time and money you've spent on trying to chase down this misfire, this is a comparatively cheap and easy thing to fix/test.
    Click here to enlarge

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Again, I've heard of other E9Xes with misfire problems being solved by bad batteries...the car does seem really, really sensitive to voltage. With the amount of time and money you've spent on trying to chase down this misfire, this is a comparatively cheap and easy thing to fix/test.
    Click here to enlarge its another thing to drain my wallet lol

    Given everything I've replaced is there any way to approach this in a more scientific way and log certain things to have a better understanding...by the time I'm done replacing everything I could've just gone out and bought another N54..
    Click here to enlarge

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
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    Ah, that's right...ok, i'll try to see if I can log battery voltages and also voltages going to the fuel injectors and coils...i already tried logging voltages on the fuel injectors and coils...will look that over again...i do seem to recall seeing that on average the cylinder 5 fuel injector voltage was the lowest of the 6...
    Sounds like you're on your way Click here to enlarge. Also, if you can log LPFP voltage, that would help too. Do you have enough resolution on your logs to see if the LPFP drops right before, or right at the very instance of the misfire?
    Click here to enlarge

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    Click here to enlarge Originally Posted by DefactoM6 Click here to enlarge
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    Sounds like you're on your way Click here to enlarge. Also, if you can log LPFP voltage, that would help too. Do you have enough resolution on your logs to see if the LPFP drops right before, or right at the very instance of the misfire?
    There's about 0.2sec resolution...problem is I can't log when exactly the misfire is triggered...i basically tell by looking at the RPMs drop a tiny bit under throttle (drop by 10-30 rpm)...during a pull the logs show RPMs going up steadily by 20-40 RPMs and then all of a sudden up top there's a sudden drop of 10-30 at the RPM that correlates to what I see in the dash when the misfire happens...what I don't know is if the misfire is JUST before or AT the time the RPMs drop..
    Click here to enlarge

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