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Thread: m50 e36 wont start then hesitation and misfire

  1. #1
    Join Date
    Mar 2015
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    Slovenia
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    E36 320i X2

    Lightbulb m50 e36 wont start then hesitation and misfire

    Hello, going to get some help over from now on.

    Been reading over 100 threads about my problem, still no solution.

    So here it goes:
    1. car doesn't start when cold ( below 15C or 59F) or when standing for more than 2 days.
    2. Cranks normally, doesn't turn.
    3. After some cranking it gets some pops of life
    4. If you push the car it starts immediately
    5. When IF it starts i get really rough Idle, hesitation, backfire, misfire and I can barely get the car moving.
    6. After a min or two when I get it moving it starts hesitating at 2000 rpm (only at 2k) like a "buckling bronco" as I read some people describe... It's really aggressive.
    6. After 5 mins the problems disappear and the car runs like new.

    I have a spare car, so I can combine stuff. The other car was fully functional before i took it apart.

    Tester says something about lambda (lambda is ignored when cold)

    I always get some ideas and then I ask myself: Why would it do that only for the first 5 mins, and after that run great? Like, it can't heat up so fast...

    P.S. Sometimes when I try to drive off when the car is warm quickly, it starts fast and then it feels like letting off the gas pedal for a sec and then pulls off again. (maybe the AC, or it's just normal)


    Replaced:
    • OEM Crank
    • OEM Cam
    • Fuel pump
    • Vanos rebuilt
    • Sparkplugs
    • Coils
    • Dme
    • Fuel relay
    • Maf - ignored when cold
    • Lambda - ignored when cold
    • New Battery, 65Ah
    • Cleaned icv
    • No vac leaks - vac leaks dont go away after 5mins
    • Tps in spec (maybe)
    • Fuel filter
    • New headgasket 2yrs ago
    • new clutch




    m50b20tu 1994 pre obd2.

  2. #2
    Join Date
    Oct 2016
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    Tenerife, Spain
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    My Cars
    1997 BMW E36 323i
    Have you tested the coolant sensor.. The one that sends the temperature to the DME?
    If it says your engine is at 80 degrees C, while in reality it's stone cold, then you'll get trouble, because it won't enrich the mixture..

    I would also check the air temperature sensor.

    Do you have INPA? Then you can see all live values and all temperatures as the DME registers them.

    I once had really bad backfires and it wouldn't start anymore, on my ex E34 525i M50. Eventually I discovered the tube from the idle control valve was loose, and it sucked so much false air that it caused all those symptoms. But that you've checked already, and also wouldn't explain why it would run perfectly fine once warm..

    One other option (maybe) is the fuel pressure regulator.. If the engine is cold, the DME can't use the oxygen sensor values to adjust the injection times. So, if, for example the FPR is working at 2.5 bar instead of 3.5 bar, you would get a very lean mixture.. Once warm, the DME "sees" that the mixture is way too lean and will adjust. On the other hand, after driving a while, the DME should save these adjustments in the adaptation values in the DME, so it should also work when cold..

    So, my first guess would be a temperature sensor. You can check them with a multimeter in the Ohm-setting. Disconnect connector and meassure directly on the sensor (probably a bit hard to get too though, below the manifold). Or you can leave the connector on, and disconnect the DME connector and measure there (if you have the pin-out table)..

    Good luck!
    Last edited by ed323i; 09-18-2018 at 07:33 AM.


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

  3. #3
    Join Date
    Mar 2015
    Location
    Slovenia
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    E36 320i X2
    Quote Originally Posted by ed323i View Post
    Have you tested the coolant sensor.. The one that sends the temperature to the DME?
    If it says your engine is at 80 degrees C, while in reality it's stone cold, then you'll get trouble, because it won't enrich the mixture..

    I would also check the air temperature sensor.

    Do you have INPA? Then you can see all live values and all temperatures as the DME registers them.

    I once had really bad backfires and it wouldn't start anymore, on my ex E34 525i M50. Eventually I discovered the tube from the idle control valve was loose, and it sucked so much false air that it caused all those symptoms. But that you've checked already, and also wouldn't explain why it would run perfectly fine once warm..

    One other option (maybe) is the fuel pressure regulator.. If the engine is cold, the DME can't use the oxygen sensor values to adjust the injection times. So, if, for example the FPR is working at 2.5 bar instead of 3.5 bar, you would get a very lean mixture.. Once warm, the DME "sees" that the mixture is way too lean and will adjust. On the other hand, after driving a while, the DME should save these adjustments in the adaptation values in the DME, so it should also work when cold..

    So, my first guess would be a temperature sensor. You can check them with a multimeter in the Ohm-setting. Disconnect connector and meassure directly on the sensor (probably a bit hard to get too though, below the manifold). Or you can leave the connector on, and disconnect the DME connector and measure there (if you have the pin-out table)..

    Good luck!
    Yeah, there are 3 sensors in the engine, the first one is for the dme, second for cluster and third for oil... right?
    I measured the sensor and it changes values, the numbers go up when its cold and down when it's hot... I got a spare one and it does the same... They both were in a 20°C environment when I tested them and they showed similar readings. Maybe he get's haywire when it drops bellow 15°C tho...

    Which air temp sensor? The one in the intake manifold? Did nothing about that one

    I dont have INPA - i only have carsoft 6.5, if INPA is better I'll look into that .

    Yeah Like I said, a lot of thing can get thrown in the bin because the car runs great when warmed up

    Thanks! You gave me a great guide what to do for the weekend

  4. #4
    Join Date
    Jun 2010
    Location
    NY
    Posts
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    My Cars
    1997 328i
    Even though you put a new battery, check the voltage after the car sat for a day or two to make sure there is no large parasitic drain. Should still be over 12v.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  5. #5
    Join Date
    Mar 2015
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    E36 320i X2
    So, I replaced both coolant temp sensor and air temp sensor.
    Tomorrow it'll be a little bit cold so I hope to see it start... or do the same thing as before.

    If it wont start, I'll check the battery voltage and remove the air filter (its 4 yrs + old, I always doubt stuff like that would cause a no start)

  6. #6
    Join Date
    Oct 2016
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    Tenerife, Spain
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    1997 BMW E36 323i
    W.r.t question about INPA.. I think you can do more with INPA, but it seems CarSoft can do a lot too.
    If you can find this screen, then it would help a lot:


    There you can verify all sensor values.


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

  7. #7
    Join Date
    Mar 2015
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    E36 320i X2
    Hey, so today the car did start but the hesitation and missfires are still here. I can't say the no start issuse is solved, i need to wait for the weather to cool down.

    Batt voltage okay, removing air filter did nothing.

    Unpluging tps and maff wont let the car pass 2200rpm - normal?
    Heres a video of what's going on when accelerating. Note that im holding full gas except once I let go of the gas once when there is a significant drop in rpm from 3k to 2k.

    https://photos.app.*******/JTaMdbvYDmnhXzVj7

    I cant see these values you showed me in my case because its a 1994, at least that is what everyone confirmed in the carsoft thread.

  8. #8
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    1997 BMW E36 323i
    Unpluging tps and maff wont let the car pass 2200rpm - normal?
    Correct. M50 and M52 DMEs can run the engine with the MAF disconnected, but then they NEED the TPS..

    With MAF connected, the fuel injection and ignition times are calculated based on the MAF, and some other variables (TPS, temperature sensors, etc).
    With MAF disconnected, the DME changes operation and uses Alpha-N algorithm, using the TPS and the RPM (and to a lesser extent temperature sensors) to calculate injection and ignition times.. So if you disconnect MAF and TPS, the DME thinks: "WTF, no way I'm gonna know how to feed this engine the right stuff".. Interestingly it still runs in your case, up to 2200 rpm. Don't ask me how the DME makes that happen (especially with a cold engine, with no O2 sensor input it seems like almost impossible)..

    P.S. video doesn't work..
    Last edited by ed323i; 09-23-2018 at 07:16 PM.


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

  9. #9
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    oh ...
    Weird link yeah. something is messing it up in this forum..

    I have two TPS sensors... both caused the car same symptoms... I could get a new one, but i think it's not worth it...

    Today I did this: The car didn't start... cranking and nothing... disconnect fuel pump fuse, cranked it, and reconnected it - the car showed some life - barely, then died when I let go of the gas pedal.
    Disconnected the MAF, same thing, but it just dies after I stoped cranking.
    Removed the fuel pump fuse again..cranked, reinstalled... and the car just started right away with Misfire, backfire on my way to work - like on the vid.

    Conclusion: The car is running too rich... maybe it thinks it's really cold, but I have no idea why because i replaced the temp sensors. Or maybe it's running normal but not all coils are firing... I would take out the spark plugs and clean them, they are probably black now...yesterday I was checking the O2 sensor, to see what's going on with this heater error with the tester, pic included, figures what color the plugs are But then again... would that affect starting?

    IMG_20180923_112916217.jpg



    Tonight it was raining, and I thing moisture has to do something with my problem... but I have no Idea why does it go away after cranking a little bit and after 5 mins... it doesn't heat up to evaporating temps in 5 mins of cranking.


    For now i'm going to check the plugs... is there a way to test if I got spark without taking everything out? Or would the tester tell me I have no spark?
    Last edited by mrsofa; 09-24-2018 at 06:01 AM.

  10. #10
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    E36 320i X2
    Update:

    It's the crankshaft sensor preventing the car to start.
    I unplugged it and it started up right away, ran really roughly, but it did..

    The crank sensor is NEW and from the Bmw dealer.
    What. The. F...

  11. #11
    Join Date
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    1997 BMW E36 323i
    Perhaps you can disconnect the cam sensor and reconnect the crank sensor and see how that goes.
    But you're probably right that it's the crank sensor. Very bad luck..

    Or: It could be bad wiring of the crank sensor (engine wiring harness).. That seems to happen now and then.


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

  12. #12
    Join Date
    Mar 2015
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    E36 320i X2
    I found out that the the part of the aluminium that holds the crank sensor in place was broken off and glued back with Jbweld.
    Capture.JPG

    The sensor is new and original bmw and in spec, like Bentley says... but the Bentley manual is not for the 320i. Also my specific model has the Siemens ecu, and the inductive sensors, and not hall. So, now I can't find if the sensor is faulty or is the sensor position correctly to the crankcase.

    I am not removing the head AGAIN to replace the chain cover, as I researched, the head has to come off.

  13. #13
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    E36 320i X2
    Solved:

    Bad ground at the Crankshaft sensor.

    (Because the sensor was glued back on, It didn't have enough contact with the metal, and when cold the metal shrinks, making the gap bigger.)

  14. #14
    Join Date
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    1997 BMW E36 323i
    Congratulations!
    Glad you could find the issue and fix it yourself.. If you'd gone to the wrong mechanic, it could have turned out very expensive..


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

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