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Thread: E36 323i 1999 m52b25 Misfire and (hissing?) noise when warm

  1. #51
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    OK.. That's interesting. The Siemens MAF "agrees" with the oxygen sensor feedback.. -8 -9 values are very normal and very low. Errors 202/203 shouldn't return. So errors 202/203 are caused by the new MAF, which sends a way too high signal to the DME, as if way more air is entering than it actually is..

    I think the Siemens MAF is just fine, at least it gives normal values (perhaps it has another problem, a bad connection or bad solder). Assuming both oxygen sensors are good.

    Vacuum leak doesn't seem to be the cause, because the DME is subtracting fuel instead of adding it (which would be the case if unmetered air enters the intake manifold/cylinders).

    But something is still off, but what it is.. I'll sleep on it and perhaps I get an idea tomorrow (works a lot of times ;-) )...


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  2. #52
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    Ok i connected the new MAF (Stark) again and went for a ride, then checked the values and here they are:

    https://imgur.com/a/hxkBp5D (14 pics)

    And here is video how it sounds while idling:
    https://www.youtube.com/watch?v=OG9NTbuBJ9E

    - - - Updated - - -

    So the fuel controls stay off and high value for air flow with this MAF, but with the Siemens one, they work BUT the car will misfire even at idle, but it shows lower air flow value.
    Last edited by reeeee; 01-04-2019 at 04:59 PM.

  3. #53
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    And is it possible that its the Alternator making this noise??
    Sounds weird that the Alternator will sound when engine warm but i really think the noise, if not another noise is coming from the Alternator.

  4. #54
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    It's too difficult for me to hear any strange noise in your movie..

    To me it's clear the Stark MAF sensor isn't good. It's giving way too high voltages to the DME, which thinks way more air is sucked in than really is. The DME then injects way too much fuel, compared to the real amount of air that gets sucked into the cylinders. Then both oxygen sensors then respond by saying: "Hey, this is so amazingly rich, this can't be good", and the DME then gets really confused and throws the 202/203 errors and stops listening to the oxygen sensors altogether.

    The thing is, with the Siemens MAF sensor, the DME and oxygen sensors agree that all values are correct. So this means coolant temp sensor, air temp sensor, MAF, fuel pressure and oxygen sensors are all fine (very probably).

    It still misfiring might then be due to wrong ignition timing. Could the timing chain have slipped a tooth or two perhaps? I'm a bit clueless now.
    Perhaps you can try and find another Siemens MAF sensor, that's known-good and see if it performs in the same way.

    Or perhaps you can try the Stark MAF sensor in a friends car, and see if it works fine there.. I expect it to be junk, the MAF sensor, and you should try and get a refund. Stick with VDO or Siemens.

    Another thought: perhaps one or two injectors are really bad and those are causing the problems? Perhaps you can have them ultrasonically cleaned by a shop. Shouldn't cost that much.
    Or perhaps a couple of coils are bad. As a matter of fact I have a set of 6 Stark coils (90 euro for all 6, including new rubber boots) in my 323i and they seem to work fine, even though the metal bracket is a bad fit and you need a lot of strength to put them on (design/quality control not so great, even though it's a German company; coils are a lot less complicated than a MAF sensor though)..
    Last edited by ed323i; 01-04-2019 at 08:08 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  5. #55
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    hmmm i could maybe try with another MAF, but one more thing is that yesterday when i changed back maf i got the MAF error code in shadow memory also: https://imgur.com/a/5gKMKxw

  6. #56
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    I'm not 100% sure, but I think you can just ignore the shadow memory.. I think it "remembers" older faults.. But keep a look on the regular error codes. If these codes migrate there, then you know there is a problem. If it only appears in shadow memory, then I think you're safe.

    One other thought: perhaps also have a look at the wiring between DME and ignition coils. Part of the wiring has a connector and is removable.
    Try to measure all wires/connections and see if a nice 0-1 Ohm shows up on each wire. Also wiggle the wires a bit while you do this. Best to measure between the DME connector and the coil connectors. You can look-up the pin numbers by checking the Bentley E36 manual or looking it up online for you M52B25, MS41 DME.

    One other possible cause could be that the DME is defective and is not able anymore to give good signals to the coils.
    Last edited by ed323i; 01-05-2019 at 06:06 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  7. #57
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    I will check the wires, but about the shadow error, I cleared it but it came back after the swap along with 202 and 203
    And I can’t understand why using the STARK MAF it doesn’t misfire when idle,
    but with Siemens MAF it misfires on idle.
    And fuel control stays off with STARK but with Siemens it’s ON - but way worse idle even misfiring

    And it’s misfiring when warm and when I press throttle on high gears or just really fast it will like sound like a boat, bluddering, idk how to describe it but it’s misfiring.

    And I have sprayed starter fluid literally everywhere without rpm change.
    Maybe I can try cleaning PCV, ICV? Even if I feel air being slight sucked in through dipstick and oil cap which should indicate it’s good it might be dirty?
    Last edited by reeeee; 01-06-2019 at 07:27 AM.

  8. #58
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    Best to find a used known-good Siemens/VDO MAF sensor.
    To me it's clear the Stark MAF sensor is really bad, and the DME can't even reach closed loop mode.

    The Siemens MAF sensor however completely agrees with both oxygen sensors. The DME gets its input from the MAF sensor, knows how much air goes in the cylinders, and calculates how much fuel to inject. That calculated amount is spot on, as the oxygen sensors indicate that the air/fuel mixture is perfect (-8, -9 values are very low)..

    So, there is another problem going on..

    My guess:
    * I don't think it's a a vacuum leak (also, if you leave the car to idle long enough, vacuum leak shouldn't have much influence because DME fully adjusts; while driving: it does have influence)
    * Could be that both oxygen sensors are bad, but I really don't think so, because they both give identical values and agree with the DME and Siemens MAF
    * I think it's the DME that's defective, or the wiring (check link in my signature for a nicely tuned DME that will give you 20HP extra as a bonus)
    Last edited by ed323i; 01-06-2019 at 07:52 AM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  9. #59
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    With these values, could a ignition coil maybe be bad?
    Since roughness on cyl 4 went up along with the misfire on idle with the Siemens MAF, everytime it misfired the number on roughness would rise, and it went up to 7000 one time while the others was not above 2.
    Or maybe stuck open injector?

    Or is this excluded from what you can see from the values would you say?

  10. #60
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    You can test this by installing a known good ignition coil in cylinder #4.
    Or you can swap for example the coil from cylinder #1 and #4. If the roughness moves to #1, then you know it's the coil..

    With the injector you can try the same. Swapping two, and checking if the roughness moves to the other cylinder. But swapping injectors is a bit more (and more dirty) work.

    Those two options are not excluded from being possible.

    You can also check if compression is low on #4.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  11. #61
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    Yeah like this video https://youtu.be/L-rarTJbc0E?t=26
    At 26 seconds, Yeah i will swap cyl 4 with cyl 3 and see, Thank you.
    But how does inpa count cylinders? like which one is cylinder 4, is it from front of engine?

    Again thank you very much for helping me, i really appreciate it alot. i'm starting to lose my mind hahah

    and btw is it safe to unplug coil while engine is running to see if it reacts? Like to know if the coil is bad
    Last edited by reeeee; 01-06-2019 at 07:45 PM.

  12. #62
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    Coolant radiator (headlights) side is #1 and firewall side is #6 .

    Live unplugging: I think BMW engineers will tell you not to do it, but I've done quite some times. Just unplug a connector and see if the engine starts to run differently. If it really starts to stumble, you know that cylinder is more or less doing its job. If there is no or only a small difference, you know the cylinder isn't working (well).

    Good luck!


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  13. #63
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    This video shows the inpa values when the STARK
    K MAF is unplugged:
    https://youtu.be/bHDOkcE0PDE

    Then I plugged it back in and engine nearly died but rpms went up then down to idle rpm, and this is value with STARK MAF:
    https://imgur.com/a/I2ztziO

    Notice engine load difference and MAF value and MAF Volt, also use of idle control valve.

    Tomorrow I will be unplugging the coils to see if engine runs rough when disconnected to see if I got a bad coil.
    Thanks.
    Last edited by reeeee; 01-10-2019 at 05:44 PM.

  14. #64
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    And I think that hissing noise that comes in after engine running is the alternator, because if I turn on headlights and rear window defroster the sound gets way worse. Idk how it could make a sound and why though.

    Weird part is I think it’s affecting the idle as well, like if I got all things on, it will run rough. I think at least can’t say I’m 100% sure. Might just be the hissing sound that’s fooling me.
    Last edited by reeeee; 01-10-2019 at 05:53 PM.

  15. #65
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    I disconnected the MAF while it was running, it then sounded like it was gonna die and ran rough but after a few sec it idled good and this is the Inpa values with MAF disconnected:
    https://imgur.com/a/aU4d3FZ

    and i also took it for a run with MAF disconnected, but still same misfire when i accelerate on high ish gears that will make it work more.
    Way better on high rpms.

    I also am 80% sure the hissing noise ive been hearing all time is from the alternator, becuase as i said when i turn on headlights and rear window defroster i can hear it loud. But when i turn all off i cant hear it (atleast not loud at all)
    And i think the sound comes from it.

    Its weird becuase the noise and the misfire came at the same time also if im correct.
    Last edited by reeeee; 01-12-2019 at 05:59 PM.

  16. #66
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    **UPDATE**

    I just tested disconnecting coils one after one on idle and after each coil disconnected it would run rough.
    So don’t think there’s coil issues.

  17. #67
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    I’m going to change spark plugs today since that’s like the only thing I haven’t checked.

  18. #68
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    Perhaps, if the alternator is bad, you can also check voltage at the battery terminal under the hood. Check it with engine off, with ignition on, with engine running at idle, and with engine running at say 4000 rpm..

    Should be 12.5, a little less than than 12.5, +/- 14 and another time +/- 14 respectively.

    - - - Updated - - -

    What also might help is creating a log file, using the testO program (search BMW testO in Google and you'll find it). Then you can see all live parameters side by side and perhaps you can spot some odd things there, when it starts misfiring.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  19. #69
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    Ok thanks i will look up that program.
    Do you think the alternator is causing the misfire when engine is warm?

    I swapped all spark plugs and i noticed it ran a bit better, felt quick at high rpms and just felt better.
    But the idle was still pending up and down once warm, and it still misfires the same when i put it under load or just step the gas all down quick.

    If i go maybe 20 km/h in 3rd gear and then full throttle it will sound like a boat while its accelerating, until i let go of the gas pedal and accelerate slowly.

    I got error code 202/203 after driving it for a bit see pic:
    https://imgur.com/a/nJCoJFW

    And i also saw on inpa while it misfired, this video:
    https://youtu.be/5veKc20_C4c

    And here is how the spark plugs looked, they are prob like 3 years old:
    https://imgur.com/a/vjEvwyt

    And btw i have had some weird electrical problems last couple days, like the car was completely dead, then i waited then it started.
    Another thing is, when i put rear window defroster on the alternator will make a hissing sound. (this only when engine is warm weird enough)
    And passanger side window wouldn't go down or up, and the day after it worked.
    Sooo electric issues, maybe it is the alternator that's bad and making the injectors, and everything else electrical mess around.
    Last edited by reeeee; 01-14-2019 at 04:34 PM.

  20. #70
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    Is this the 202/203 codes with or without MAF sensor and the Siemens or the Stark one?

    The low oxygen sensor voltage means the mixture is too rich, according to this page: http://www.bimmerboard.com/forums/posts/1232542 (M52 uses expensive titanium oxygen sensors).
    The DME is unable to compensate for this. It isn't allowed to make the mixture any leaner than it's already doing.

    So this means the DME is getting a signal from the MAF sensor (+ coolant temp sensor, air intake temp sensor) that indicates a certain amount of air is sucked into the engine. It then calculates how much fuel it should inject, and does this. But then keeps getting feedback from the oxygen sensors that the mixture is way too rich. Then it leans out the mixture, until it hits the point where it will trigger an error, the 202/203 errors.

    So, most probably the MAF sensor is giving a too high voltage, indicating a higher than real air flow into the engine. Or the coolant sensor keeps saying the temperatures are still in the warming-up range, which also causes the DME to enrich the mixture. And in lesser extent the same for the intake air temperature; if it registers too low, the DME will enrich the mixture a bit too if I'm correct (I'm not 100% sure because a MAF sensor registers the mass of the air, so perhaps temperature has no influence, whereas with a flappy-style AFM sensor it does).

    Spark plugs don't look that bad I think. They should last a long time in the M52, but it's best to replace every few years (or earlier if you're driving a lot of kilometers)..
    Last edited by ed323i; 01-14-2019 at 05:10 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  21. #71
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    It will even misfire and behave the same if I disconnect the MAF which gives low values and low volt on Inpa, and I have the STARK MAF in right now.
    I will test my friends MAF tomorrow.
    But it behaves the same with/without maf.

    And considering the electric faults I’ve been having, could it be the alternator that interferes with all electric components making the engine have rough idle and misfire?
    And the noise I hear from the alternator when it’s under load. (And warm)

    I googled it up and got this:
    Drops in electrical output from a failing alternator can cause these systems to malfunction, leading to a poorly running engine. Symptoms will be rough idle, misfires, poor acceleration, hesitation and stalling.

    And I got basically all of these symptoms 🤔
    Last edited by reeeee; 01-14-2019 at 05:21 PM.

  22. #72
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    If alternator is bad, or a high amp connection at the battery or at the alternator or at the engine (ground cables) is bad, then you can get strange symptoms indeed.
    You can test with a multimeter what voltages you see (check my post #68). You can also disconnect battery terminals and reconnect them (do not over-torque them, be gentle) and check all big wires in the engine bay and re-torque them.

    If you haven't got a multimeter, go buy one, and watch some tutorials on youtube on how to use it. Helps a lot.
    You can also have the testO program log the voltage, along with MAF air flow, O2 sensor values, fuel trim, coolant temp sensor, air intake temp sensor. That should help a lot too. Download here: https://www.bimmerforums.com/forum/s...ime-graph-view .


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  23. #73
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    I don't understand your test of unplugging the coils. Of course it's going to run rough with an unplugged coil since you're immediately running off of 5 cylinders.

    If you suspect the alternator, run the engine briefly with no belt. Should let you know if it's something on the belt drive at least.

    Swap the coils and see if the code/INPA data follows it. That was how I found mine (post #22).

  24. #74
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    I tried testo but I couldn’t get it to work, I just got errors but I’ll try to get it to work. And yeah I got a multimeter, I will check as u said.

    The test was something a lot of ppl said online, apparently if coil #5 is bad and making it run rough, unplugging it would’nt make much of a difference. I think. I heard a Big difference though.

    I forgot to mention it but I changed my battery to a 100ah one, it almost didn’t fit haha, now when I think of it this misfire might have come a while after I changed it, because the batter I had before was dead after I accidentally drained it few times, and it would somedays not start. (Maybe the old battery damaged the alternator?)
    Now when I think of it, I didn’t tighten the minus pole with the bolt, but it’s not loose it just sits in there so I don’t think that’s it since it’s not problem when car not warm but I’ll definitely fix it.

    The thing is why I’m thinking of the alternator is that when it’s cold, it’s runs better and doesn’t make weird sound. Even when I put it on load with like read window defroster, but when it gets warmed up the alternator will make a weird “hissing” noise, along with the car misfiring and having rough idle again, same time as the noise comes. When it’s warm.

    That’s why I think it’s alternator because it seems weird that I get misfire and noise from alternator at the same time.

    And thanks for spending time helping me, I really appreciate it. Idk what i would have done else.
    Last edited by reeeee; 01-14-2019 at 06:17 PM.

  25. #75
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    I don’t understand why it will run more rough with the original MAF though.

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