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Thread: 1993 320i BMW M50 Engine Puzzle. Help Needed!

  1. #1
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    1993 BMW 320i

    1993 320i BMW M50 Engine Puzzle. Help Needed!

    Hi All,

    Before writing my problem I do like to say that I googled and read every possible page related to the problem. I did anything I can to find any trace that could lead me to a solution with my car. I did write this thread because I reached all dead ends with no possible solution.

    My car:

    BMW 1993 320i M50 Engine Single VANOS with Siemens MS40.1 DME and EURO spec (No CEL), odometer 205xxx km

    I did not post in the E36 section because the same engine is used in E34.

    Problem:
    The engine is not starting properly. It starts very hard and rough with not all cylinders firing. It backfires while starting as if it has no idea about ignition timing. After cranking up for sometime the engine keeps trying to start till starts finally but some cylinders are firing and some not. I have to leave the car till it warms up completely. When I say completely I mean it is not related to the Temp Gauge which reaches the middle. I mean till the engine warms up and the heat is distributed everywhere around the engine. After that I turn the car OFF and turn it back ON. It fires up immediately and very smooth as if there was no problem at all! All cylinders fire properly.

    Here is an important hint which leads me to think that it is an electrical problem:
    Sometimes even when it is very cold. I start the car and it fires up immediately and very smooth (all cylinders working). It stays like that for about 20 seconds and then stops (as if someone turned it off)
    When I try to start it again, I go through the same loop of misfiring cylinders.. warming up..turning off and ON then finally drive.

    One more thing. When Its very cold (0-10 degrees C). The car won't start at all. I have to remove the fuel pump fuse, start the car (with misfiring), and then return the fuse immediately and leave the car for warming up. Sometimes I thing it fires only two Cylinders because the engine shakes too much and makes a strange firing sound that can be heard twice every second. (Like a diesel engine)

    Here are the things that I tried already:
    - Injectors: All tested and cleaned twice and are working without problems.
    - Spark plugs: Replaced and I am sure the old ones had no problem.
    - Fuel pressure regulator: Tested and working without problem.
    - Fuel pump: Tested and its VDO with less than a year old.
    - MAF sensor + TPS all working properly.
    - Camshaft Position sensor: Replaced and the new one measures without any errors when tested with Ohmmeter (I know its not dependable but its kind of gives a clue if it works or not).
    - Crankshaft Position Sensor: The usual Ohm test looks fine but I didn't replace it because if it has any error, there will be no spark or ignition at all.
    - ECT sensor: Replaced and I compared the old one with the new one and both had the same resistance with temp.
    - I replaced the Battery (just to be on the safe side).
    - I tried to use the hair drier to heat every sensor alone and than start the car. Nothing helped. I tried to heat the DME and start the car. I failed. I tried to heat the spark plug coils. I also failed.
    - The DME compartment is dry and it looks well.
    - I cleaned ICV just in case.
    - I checked the intake manifold for any leaks.



    I tried every possible combination of disconnecting each sensor and trying to start the car. Nothing changed at all (Except when I disconnect the Crank sensor, it wont start at all)

    Did I try to diagnose it?

    Yes of course. BUT I could not connect to DME. The Diagnose device I used is Foxwell and I used it before on my car, it was working very well. I suddenly lost all communications with any DME/EML. Now I cannot connect to any Module.

    The car has no smoke at all. It accelerates and drives very smooth without any problems when it's warm. I drive it 4-5 hours continuously without turning it OFF. My problem is with starting in cold weather only. It starts completely fine for the rest of the day.

    Is it the DME? Or something wrong with Crank Position Sensor?

    I am living with this issue for two months and it drives me totally crazy. I owned this car for more than 12 years and I was able to repair and solve every problem with it except this one.

    Any possible ideas?

    Why sometimes the engine starts smooth even when it's cold?
    If there's an error related with any sensor or other fuel delivery system, why the car accelerates and driver extremely well after it gets warm?
    I feel like the DME refuses to fire the cylinders properly for some reason.
    Last edited by peacemaneng; 01-19-2020 at 06:19 PM.

  2. #2
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
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    Welcome to the Forum!

    A very good write-up, and thank-you for taking the time to put it all up.

    Since you lost communication with the DME, that is where I would start first. Do you have a wiring diagram for your car? If not, look here: https://www.newtis.info/

    I would start with the diagnostic plug and work your way to the DME using a multi-meter. You will want to find out if there is a wire cut or has been chewed on by an animal. While it is limited you can see some live data, not sure which Foxwell you have so it might not be able to do such. Do you have a laptop laying around? I like use INPA, which is a BMW diagnostic program. You can get a cable for about 25 bucks and the software tends to be free on the internet. With INPA you can read the live data, and talk to all the other modules in the car as well. Now some laptop require special drivers, so if it isn't connecting, that could be the problem.

    The only thing I didn't see you test is the coils, which can be done using a ohm meter or a multi-meter set to ohms. IIRC pin 1 and 15 with a value of .6 to .8




    Darin
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  3. #3
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    1993 BMW 320i
    Thank you dworthy for reading and replying to my post.

    I tried to follow the wires and to find any cut or exposed wires but no luck till now. I have the INPA cable and the software but still can't communicate to the DME (the same as Foxwell device). The Foxwell device I'm using is Foxwell NT510 with installed BMW software. I used it before to reset my Airbag, check DME, Transmission module, and Climate system. It was working fine.

    I did a check on the coils as you said. They looked like OK.

    Update:

    After doing experiments. I did found that the error for all this is:

    CRANKSHAFT SENSOR

    - When I disconnect the crankshaft sensor and the car is cold, the car starts (after 20 seconds cranking) and with firing 6th cylinder only.
    - When I connect the crankshaft sensor and the car is cold, the car refuses to start at all. It cranks and sounds just going to start with random ignitions and backfires. It never starts.
    - When I connect the crankshaft sensor and the car is warm/hot, it starts very well with all cylinders.

    My questions:

    - If I disconnect the Crankshaft sensor, how it is possible to read the rpm without the crankshaft sensor?
    - Can the DME depend on the camshaft sensor only to read rpm?
    - According to every post I read about the crankshaft sensor: No crankshaft means No ignition. Then how my car starts without the crankshaft sensor? is camshaft sensor only enough for this?

    I'm going to get a new one in two days and see the results.

  4. #4
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    Hello and welcome to the forum. Strange how that car starts without a crankshaft sensor... If I remember well the camshaft sensor serves to double check the crankshaft one when starting the engine, but I don't see how it can start without one as well. Perhaps it explains why it only fires 1 cylinder.

    Have you checked the grounds (engine ground, ground straps with 2 of the coils, a brown wire that bolts next to one of the coils and battery ground in the trunk). It might not be related at all but when there is a seemingly electrical issue it can't hurt to check those.
    "If you have integrity, nothing else matters. If you don't have integrity, nothing else matters." Alan K. Simpson.
    5spd E46 "3XX": 328i engine, 330i Intake and exhaust, CAI, 323i diff.

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