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    Misfires, lean & negative fuel trims. Help!!

    Here is the situation. I have a n54 FBO 335i, running Cobb Stg 2 + Started having misfire codes and limp mode, generally on bank 2 (cyl 4,5,6). This would usually happen on at least 2 cylinders. Acceleration is jerky and the car lacks punch. I would occasionally get a misfire on a bank 1 cylinder as well. Complete the simple fixes. I change all the bank 2 coils and changed all the spark plugs and gapped them. The old ones looked pretty good, number 6 was a but darker than the others, but that is common for either 5 or 6. I also cleaned the vanos solenoids. I changed the bank 2 O2 sensor today, but issue still isn't fixed. It was a longshot since both banks are lean, but I noticed some sluggish and occasionally erratic reading on bank 2.


    This didn't fix the problem and I had to dig deeper. Started taking some targeted logs and realized that I was having a lean condition at WOT, sometimes approaching 20 AFR. Bank 2 AFR is always higher than Bank 1, but neither bank is hitting AFR targets. I'm not sure whether misfires are causing the lean condition or the lean condition is causing misfires. Here is the kicker... Even though AFR is high, long term fuel trims are very, very low, between -30 and -45 on both banks. This is counter intuitive. Why would fuel trims be negative if the engine is running lean??


    Some other things to note. Car starts and idles perfectly, not a hickup. Minimal fuel trims at idle and most driving. Fuel pressure is good, so I've ruled fuel pumps out. Voltage and grounds have been checked. Timing corrections are minimal to none on these diagnostic logs I took. Never have any lean or O2 sensor codes. Walnut blast valve cleaning was done about 20K mi ago. Here are some graphs. I tried Datazap, but it wouldn't plot the logs for some reason.


    HELP! Thanks....


    Here is a log where I captured a misfire code and limp mode (where fuel mode changes from 2 to 15)
    Click here to enlarge


    Here are a few other before changing the bank 2 O2 sensor
    Click here to enlarge
    Click here to enlarge


    Here is after the O2 sensor change
    Click here to enlarge
    Click here to enlarge

  2. #2
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    Hmm...I'm not terribly familiar with the Cobb platform, but have you tried resetting your O2/Lambda adaptations? What fuel are you running?

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    Did the misfires start when you installed the Cobb and the new map or were you running that map for a while before it started to misfire?

    Could it possibly be injector failure? Doesn't really explain the negative fuel trims when running so lean though.
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    Repped for some answers.

    As far as trims being negative when you're running lean... the only thing I've experienced was some DME confusion when fooling around with ethanol maps. Sometimes the trims will get wacky and they do not seem to correct themselves. What do your short term fuel trims look like?

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    Misfires are most likely lean misfires. Can you uninstall the AP and go to a stock type map and reproduce the symptoms? Your situation is odd, it's like the computer is still in closed loop but going the wrong way, I've seen the kind of afr issues when the dme goes to open loop but that usually freezes trims. Sensors aren't swapped are they? Keep us informed what you find.

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    Can you log duty cycle of the injectors.... you may be maxed out on DC % or you have an injector/s block/problem.
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    Really appreciate the replies and helping to troubleshoot this. It seems to me that the car would run right if fuel trims weren't out of wack. I have a PTF tune that the same thing was happening on and I swapped back to the standard Cobb stg 2+ for a while for troubleshooting.

    Click here to enlarge Originally Posted by EvanL Click here to enlarge
    Hmm...I'm not terribly familiar with the Cobb platform, but have you tried resetting your O2/Lambda adaptations? What fuel are you running?
    I have reset the ECU with the cobb before and the same thing happens. I did a resent after changing the O2 sensor and did a trial 'learning' run before the last 2 logs in the 1st post. I'm running shell 93.

    Click here to enlarge Originally Posted by froop Click here to enlarge
    Did the misfires start when you installed the Cobb and the new map or were you running that map for a while before it started to misfire?

    Could it possibly be injector failure? Doesn't really explain the negative fuel trims when running so lean though.
    I've run these same standard cobb and PTF maps before and not have this issue. This has been happening for the last 2 mo or so. Thought about injector failure, but that would case issues all the time and probably a rough idle which I don't have. Changing injectors would be the next thing to try, but I don't think it will fix the problem.

    Click here to enlarge Originally Posted by SCGT Click here to enlarge
    What do your short term fuel trims look like?
    Haven't paid a lot of attention to short term fuel trims, but when I have looked, they didn't seem to be unusually large in either direction.

    Click here to enlarge Originally Posted by V8Bait Click here to enlarge
    Misfires are most likely lean misfires. Can you uninstall the AP and go to a stock type map and reproduce the symptoms? Your situation is odd, it's like the computer is still in closed loop but going the wrong way, I've seen the kind of afr issues when the dme goes to open loop but that usually freezes trims. Sensors aren't swapped are they? Keep us informed what you find.
    Agreed that these are lean misfires. I could uninstall cobb, but loose the ability to data log then. Next step will probably go to a cobb stock map. I could then uninstall cobb after that step and see if any codes are thrown. O2 sensors are definitely not swapped.

    Click here to enlarge Originally Posted by Group.america Click here to enlarge
    Can you log duty cycle of the injectors.... you may be maxed out on DC % or you have an injector/s block/problem.
    I could try this, but it doesn't explain what is happening with fuel trims.Would be unusual to run out of IDC on pump maps. They even work for ethanol maps once you keep the fuel pressure up.

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    It wouldn't have been plugs and coils in this case as fueling is the primary concern not ignition. I'd reset adaptations and relog. If it reoccurs I'd replace injectors provided that the hpfp and lpfp pressures are following target and not the cause like you mentioned. Feel free to shoot over any logs my way any time.
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    I uninstalled the AP, and re-installed with a stage 0 (stock) map. Took 2 logs while running an errand. Didn't get too high up in RPMs, but it looks like the same thing is happening. Acceleration was still jerky. Fuel pressures still meeting targets.

    Click here to enlarge

    Click here to enlarge


    Click here to enlarge Originally Posted by dzenno@PTF Click here to enlarge
    It wouldn't have been plugs and coils in this case as fueling is the primary concern not ignition. I'd reset adaptations and relog. If it reoccurs I'd replace injectors provided that the hpfp and lpfp pressures are following target and not the cause like you mentioned. Feel free to shoot over any logs my way any time.
    Appreciate the offer. I will send some logs. I'm hesitant to change injectors, but that might be my next step. I can't reconcile the fuel trim corrections that the ECU is making for a lean running condition even if there is an issue with some injectors.

    Anybody ever see something like this?

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    Did you clear fuel trims? I'm not certain that uninstall/reinstall of the Cobb does that, and I'm very certain that changing maps does NOT reset them. I believe you need either Bavarian Technic tool or INPA to reset fuel trims.

    Log both short term and long term fuel trims and lets see if they're mirroring each other. Sometimes the DME gets confused and you'll have max add on one and max subtract on the other. Not optimal.

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    Click here to enlarge Originally Posted by SCGT Click here to enlarge
    Did you clear fuel trims? I'm not certain that uninstall/reinstall of the Cobb does that, and I'm very certain that changing maps does NOT reset them. I believe you need either Bavarian Technic tool or INPA to reset fuel trims.

    Log both short term and long term fuel trims and lets see if they're mirroring each other. Sometimes the DME gets confused and you'll have max add on one and max subtract on the other. Not optimal.

    I thought that an ECU reset on the Cobb also cleared all previous learning. Can anyone else confirm if this is or not the case? I haven't used inpa before, but maybe I'll have to get a setup going to use it. I'll get some logs including short term fuel trims as well. Thanks.

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    No, resetting the ECU on Cobb does not reset adaptions. This needs to be done in INPA or with a BT cable.

    I'd recommend logging your STFTs as mentioned above. Those and/or poor adaptions may be walking your LTFT's out, your DME has lost the ability to compensate, and this is forcing your car to go lean.

    Also, if possible, upload your logs to datazap and log fuel pressures. Click here to enlarge

    FTR, I personally don't suspect injectors as both banks are wonky, go way positive (nearly maxing out), and then diverge after they start going negative and the DME is clearly losing it. So at least for the time being...I'd hold off on that expense. Click here to enlarge
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    I found this image of a guys logs that had a similar issues. Thought I'd post them up as an example.

    Click here to enlarge

    Prior to this, this person had replaced coils, plugs, injectors, and spent a lot of money. Click here to enlarge The fix....adaptions reset.

    Here's a link to the thread where I discussed it.

    http://www.n54tech.com/forums/showthread.php?t=23183
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    A cobb can't reset adaptations? What about the adaptations reset with a Procede and JB4? Are they just the same as resetting them via INPA or a BT cable?
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    The log Steve posted looks more like what I've seen before when the computer locks trims. I guess it only locks STFT, but most logs I've seen this on were procede and one guy with a jb4 and they only monitor stft. I don't remember their final fixes, but it was sporadic usually not all the time for them.

    But I second using INPA or BT to reset adaptations, cobb never seemed to reset much for me.

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    Click here to enlarge Originally Posted by SteveAZ Click here to enlarge
    No, resetting the ECU on Cobb does not reset adaptions. This needs to be done in INPA or with a BT cable.

    I'd recommend logging your STFTs as mentioned above. Those and/or poor adaptions may be walking your LTFT's out, your DME has lost the ability to compensate, and this is forcing your car to go lean.

    Also, if possible, upload your logs to datazap and log fuel pressures. Click here to enlarge

    FTR, I personally don't suspect injectors as both banks are wonky, go way positive (nearly maxing out), and then diverge after they start going negative and the DME is clearly losing it. So at least for the time being...I'd hold off on that expense. Click here to enlarge
    Completely agree with this assessment. I'm doubtful it the injectors considering the corrections the ECU is making. Odd the that ECU can work its way into a knot like this. I took two more logs this morning and STFT are pegged +ve while LTFT are significantly -ve and the car is not correcting those adaptations. This is still on stg 0 map. I do log fuel pressures and targets and those always look good. I am working on an INPA setup to reset adaptations. I tried datazap over the weekend, but it would not plot the logs for some reason after I uploaded the files. I will try again today to see if I can get through.

    Click here to enlarge

    Click here to enlarge

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    ^ These make a bit more sense when you add in the STFTs. Obviously the STFT should be learning into the LTFT, so that's still wonky. I'm sure these guys and Dzenno can get you sorted, but I'm happy to review some logs as well. Try resetting those adaptives as others have stated, and see if the start to relearn as expected or if they immediately shoot to full negative and positive again.

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    Click here to enlarge Originally Posted by GoodToGo Click here to enlarge
    Completely agree with this assessment. I'm doubtful it the injectors considering the corrections the ECU is making. Odd the that ECU can work its way into a knot like this. I took two more logs this morning and STFT are pegged +ve while LTFT are significantly -ve and the car is not correcting those adaptations. This is still on stg 0 map. I do log fuel pressures and targets and those always look good. I am working on an INPA setup to reset adaptations. I tried datazap over the weekend, but it would not plot the logs for some reason after I uploaded the files. I will try again today to see if I can get through.

    http://www.DomesticBoost.com/images/.../eMMMp55-1.jpg

    http://www.DomesticBoost.com/images/.../TXEaMHh-1.jpg
    I've seen this behavior probably a dozen times and the only way to fix it is ressetting lambda adaptations using INPA, the Cobb ECU Reset WILL NOT fix it.
    @Josh@Cobb, you guys ready to add that Lambda adaptation reset feature yet? Click here to enlarge
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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
    I've seen this behavior probably a dozen times and the only way to fix it is ressetting lambda adaptations using INPA, the Cobb ECU Reset WILL NOT fix it.
    @Josh@Cobb, you guys ready to add that Lambda adaptation reset feature yet? Click here to enlarge
    We don't have it yet, but its on the list. I've only seen this on a handful of cars and only after swapping to/from an ethanol map. Even then, the trims always brought themselves back to where they should be within a few drive cycles. I may need to bump priority on this one.
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    Click here to enlarge Originally Posted by Josh@Cobb Click here to enlarge
    We don't have it yet, but its on the list. I've only seen this on a handful of cars and only after swapping to/from an ethanol map. Even then, the trims always brought themselves back to where they should be within a few drive cycles. I may need to bump priority on this one.

    Just FYI, my trims didn't correct themselves after many drive cycles. Mine were jacked for quite a long time until I figured out the BT adaptations reset trick. They've been fine since. 2007 i8aos, MD80.

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    Click here to enlarge Originally Posted by Josh@Cobb Click here to enlarge
    We don't have it yet, but its on the list. I've only seen this on a handful of cars and only after swapping to/from an ethanol map. Even then, the trims always brought themselves back to where they should be within a few drive cycles. I may need to bump priority on this one.
    Yes, please put it high on the list for the BMW platforms. My trims definitely are not correcting themselves after weeks and a few different maps. I haven't used an ethanol map. Seems like this happens often enough even though it is not very common. No lean or mixture codes thrown either to point to the issue, just misfires.

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    Got data datazap to work on those last 2 logs which include STFT on stg 0 map. Still working on getting INPA up an running. It's a pain and have an error that I am working through. Hopefully I get it working today.

    http://www.datazap.me/u/bmr8619/stag...20&zoom=21-134


    http://www.datazap.me/u/bmr8619/stag...20&zoom=38-168

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    1 out of 1 members liked this post. Yes Reputation No
    Got INPA sorted out and the adaptations reset. Loaded back up my PTF map. Car hasn't felt this good or run right for that matter for quite a while. Here are two new logs. LTFT is probably still settling in, but AFR is on target. No more hesitation on acceleration and car feels strong again. Issue was bad adaptations all along. Glad it's fixed. Will have to keep an eye on these now.

    http://www.datazap.me/u/bmr8619/afte...-18&zoom=14-98

    http://www.datazap.me/u/bmr8619/afte...-20&zoom=46-90

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    Does anyone know if the Procede or JB4 adaptations reset properly reset adaptations or do you require INPA or a BT cable to do it properly?
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    Click here to enlarge Originally Posted by froop Click here to enlarge
    Does anyone know if the Procede or JB4 adaptations reset properly reset adaptations or do you require INPA or a BT cable to do it properly?
    Anyone?

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