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Thread: Engine pulses, flat spots, chasing stioch?

  1. #1
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    Engine pulses, flat spots, chasing stioch?

    I first noticed this accelerating in like 2nd and a bit in 3rd gear, I figured it was the vanos kicking in I was feeling or something.. It feels like good power then gets flat for 200 RPMs or so and then good power and then flat again and back to good power.. I can only really feel it in lower gears from 2k-3.5k RPMS.. It felt like flat spots that are RPM related but today I noticed new clues..

    I found that I can see these flat spots in the MPG gauge! Well, if it's not completely buried on the low end that is.. If I accel not completely WOT, around/above 8mpg or so, I can see these flat spots in the MPG guage wiggling... The MPG gauge goes up a MPG or 2 when it gets flat and goes back down for good power, comes back up a touch when it gets flat, over and over, steady rythem..

    I did some testing by pulling against my breaks in 4th gear at about 3k RPM steady and the MPG guage wiggles back and forth in this steady rythem, about 1 second per wiggle..
    Now that I notice this rythem I think I can faintly hear it in my idle also but that is off the scale.. It is more pronounced with some engine load..

    Now, I know that the MPG guage is based off of injector open time vs speed, so this means that my injector open time is varying back and forth, rich/lean, when under load, and I am feeling it as flat spots in my accel.. I think..

    I have been around some ancient K-jet lambda and know how it will chase the AFR back and forth across stioch in a steady rythem like this, when the narrowband crosses stioch it turns around and heads the other way and over and over in a constant rythem crossing stioch..
    This feels like what this m3 is doing.. No CEL..

    So, what do I do?
    I think I might replace the O2, maybe it is fouled up, getting lazy/slow or something.. IDK.. Maybe I am way off in my diagnosis..
    I don't want to just start throwing parts at it. I bet one of you guys have witnessed the same symptoms and can tell me from experience what is going on..
    I explained my hunch.. How far off am I?

  2. #2
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    Your diagnosis seems reasonable. I'd replace the O2, clean the maf, and check the tps. All can be done very inexpensively. If it persists I'd look at the knock sensors. I agree with you that it sounds like he DME is getting a weird input somewhere.

  3. #3
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    I had a coil go bad and the symptoms were the same. It eventually threw a CEL after the misfire got worse, but originally it was a few weeks like what you are describing.

    - 98 m3, techno/anthrazit cloth, 124k and officially worthless - 89 m3, alpine/black 143k and officially old - 2000 323it, tiag/grey, 169k and officially boring

  4. #4
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    Well...
    I Got new sparkplugs from Dr. Vanos so yesterday I put those in and ran a ground wire across all of my coils..
    One of the coil studs is missing and a couple of the others feel like they want to pull out too, not good..
    I think I might drill and tap some of the unused stud bosses for more studs rather than try to heilicoil the old holes. Is this valve cover magnesium? It feels like it.. Every coil has atleast 1 good stud as is though and I'm sure they are grounding..

    The coil-sparkplug boots seem in bad shape.. The ends want to flake apart so I ordered a set of new bremi boots though my coils are all bosch I read a thread that the bremi boots will work fine..
    These spark plugs are bosch ones with the 2 tips on them, from Dr. Vanos.. I thought that those guys would know what plugs to use.. Old plugs look absolutely perfect though, all exactly the same nice and clean nice tan etc..

    BUT, now after doing this the car has a random miss at idle. Idles fine but misses every once in a while, symptoms in the OP have not changed, still no CEL..
    I hope the new boots will cure it..
    These plugs are bosch 7402 with the split tips and I think I ran across a thread something about they can cause crap idling.. Do you think their is any chance these new plugs themsevles have caused my symptoms to worsen?

    I have a very new used O2 out of my old 318 obd1 but I can't get this M3 O2 out, I'll have to drop the exhaust to do it so I'll save that for a last resort.. I am very leary of exhaust bolts especially in manifolds.. They instill a primal fear in me..

    I couldn't find anything open yesterday to grab a can of break clean for my MAF so I'll do that today..
    Need to grab my old bentley while I'm at my moms and hope it covers this M3 to check the TPS and coils..

  5. #5
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    When I've had bad coils I felt dead spots more in high gears. Did you gap the new plugs? Improper gaps could cause bad idle.

    Bad knock sensors won't throw a CEL. Neither will unplugged knock sensors. But bad knock sensors can throw false "knock signal" to your DME when the harmonics of a specific rpm triggers them. Try unplugging them, it's free and maybe your issue will go away?

  6. #6
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    Quote Originally Posted by weedshoes View Post
    When I've had bad coils I felt dead spots more in high gears. Did you gap the new plugs? Improper gaps could cause bad idle.

    Bad knock sensors won't throw a CEL. Neither will unplugged knock sensors. But bad knock sensors can throw false "knock signal" to your DME when the harmonics of a specific rpm triggers them. Try unplugging them, it's free and maybe your issue will go away?
    I did not gap the plugs but they all seemed the same and pretty close gaps..
    To my surprise they are weird and look like this...

    Maybe if the coil boots don't fix it I'll try the old plugs again and see if my idle goes back to perfect like it was..
    Last edited by fasteddie313; 08-08-2017 at 01:06 AM.

  7. #7
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    Cleaned the MAF and I think it runs a little better, may be plasebo, but the flat spots/wiggling MPG guage are still there and it still misses at idle a little.. It's like 1 miss every 5 to 20 seconds.
    rrrrrrrDrrrrrrrrrrrrrDrrrrrrDrrrrrrrrrrrrDrrrrrrrr rrrrrrrrDrrrrr not constant..

    https://www.youtube.com/watch?v=0eS4VDeU81g
    Last edited by fasteddie313; 08-08-2017 at 01:23 AM.

  8. #8
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    I had bad luck with Bosch plugs and many others have as well. NKG BK6RE are the documented plugs of choice for having a stress free choice. I'm not saying it's your problem, but it's a cheap start to rule something out.

    - 98 m3, techno/anthrazit cloth, 124k and officially worthless - 89 m3, alpine/black 143k and officially old - 2000 323it, tiag/grey, 169k and officially boring

  9. #9
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    Quote Originally Posted by notMpowered View Post
    I had bad luck with Bosch plugs and many others have as well. NKG BK6RE are the documented plugs of choice for having a stress free choice. I'm not saying it's your problem, but it's a cheap start to rule something out.
    Those nkg are what I use. Never had a problem with them.

  10. #10
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    Yep. You and I and many others love our NGK plugs.

    - 98 m3, techno/anthrazit cloth, 124k and officially worthless - 89 m3, alpine/black 143k and officially old - 2000 323it, tiag/grey, 169k and officially boring

  11. #11
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    I put the old plugs back in and the idle miss went right away..

  12. #12
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    As luck would have it, my 325i started doing this today. I think I got bad gas. How long has yours been acting up?

  13. #13
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    Quote Originally Posted by weedshoes View Post
    As luck would have it, my 325i started doing this today. I think I got bad gas. How long has yours been acting up?
    I think ever since I got it, less than 1k miles still..
    Runs pretty darn good other than I can feel these power pulses while accelerating and I think I can see them on my MPG gauge needle wiggling/fluctuating..

    I think I read that it only actively adjusts AFR mixture from the O2 sensor input at idle and cruise, where it runs basically perfect, so I think that rules out the O2 causing it..

  14. #14
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    Quote Originally Posted by weedshoes View Post
    Bad knock sensors won't throw a CEL. Neither will unplugged knock sensors. But bad knock sensors can throw false "knock signal" to your DME when the harmonics of a specific rpm triggers them. Try unplugging them, it's free and maybe your issue will go away?

    I unplugged my knock sensors and it made my same symptoms but like multiplied them by 10..
    The pulsing during acceleration got worse to the point where it would even miss/sputter a tiny amount during the flat spots..

    AND it threw code 1226, knock sensor #2

    But it did not throw 1225 code for knock sensor #1, and you said it should not throw a code.. So what does this mean?

  15. #15
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    Still trying to nail this down..

    Have a new fuel filter on the way, put a new intake boot on but I think I ripped it myself taking the intake off so many times..

    Accelerating it just feels like the AFR swinging rich-lean-rich-lean and I can feel it in the power produced strong pull-weak-strong pull-weak..
    Happens from low 2k's and seems to disappear about when the vanos kicks in.. Most noticable in low gears..
    Looks the same as my mpg gauge wiggling back and forth during constant accel in a high gear, like pulling a hill, but I can't feel it then, when I can feel it I can't see the MPG gauge..

  16. #16
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    They make MAF cleaner, but since you used brake cleaner on it that could cause more problems.
    Check the TPS with a meter to see if what it reads when slowly opening the throttle.
    [IMG][/IMG]

  17. #17
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    Right, I need to check that tps but my meter is fubar..

    I thought I read here on this forum to clean the MAF with brake parts cleaner..?

  18. #18
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    They make a cleaner for MAF. You may want to consider getting a code reader that can read and record in real time. I have a KIWI2 and a phone app. You can set it up to monitor short and longterm fuel trim, O2 sensors, etc. You may be having something simple like a vacuum leak that would show in fuel trim adjustments. If nothing else they are fun to play with!

  19. #19
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    This symptom has never gone away after driving another 8k miles or so and I still get no CEL other than very rarely it throws a VANOS CEL but it goes back away.
    The VANOS is brand new from Dr. VANOS (about 8k miles) and all of the timing chains, sliders, and tensioners are new (about 15k miles)..
    I think I did the VANOS right.. The only part left is the VANOS solenoid right? But this symptom doesn't sound to me like a VANOS thing, idk..
    I did test the VANOS solenoid by engaging it at idle and it does work but maybe slowly (it was a while ago) at idle..
    I think they can be taken apart and cleaned or something.. I'll have to look that up further..

    I have new BK6RE plugs on the way, and 9 used OEM coils on the way for swap testing, and the new bremi boots.
    It doesn't seem like an ignition problem because it is showing up in fuel (injector open time) via the MPG gauge, but I read coils can do crazy things to BMWs and cause crazy symptoms so who knows..

    I have INPA that is working good on my 06 X5 and the round plug adapter for the under hood connection on the M3 but I can't get it to work on the 95 M3.
    I looked it up a bit and it is pretty confusing..

    Honestly this slight surging thing feels like a DME problem to me.. Like a fuel map problem..
    I am suspicious that it has a crap ebay chip in it or something causing this.. I want to check and see what chip is in there and almost feel like swapping in a known good stock chip to see if that fixes it..
    PO mentioned nothing about a chip but I am suspicious..

    What causes a MPG gauge to wiggle back and forth a bit like a clock pendulum at a constant RPM and TPS and even at WOT?
    Hmmmm....

    I can only feel it in the power output in lower gears and harder acceleration I think because that is the only place it has enough torque change magnitude with the swings to the rear wheels for me to feel it in the power output.

    It isn't that bad, very derivable, but really annoying to know something isn't right, and it MUST be down on power a bit because I can feel it pulls harder when the MPG gauge swings to the right toward richer, and if it is swinging lean enough for me to feel loss in power that can't be good for the engine so it is keeping me from using this engine like it should be used (high RPM) because I don't want to rag on it and hurt it..

    I drove it like this for a long time hoping that it would get worse enough for me to be able to come to a diagnosis or worse enough to throw a CEL so I can figure it out but it has not changed..
    E36 M3 S50 - E53 X5 M54 - 1980 Porsche 931 - 2001 Impreza RS25

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