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Thread: E30 325i 1987 engine cuts out suddenly

  1. #1
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    1987 BMW E30 320i Coupe

    E30 325i 1987 engine cuts out suddenly

    Hi. I have a E30 325i from 87, prefacelifted with the motronic 1.1 old motor. I had almost a complete rebuild motor while restoration, with new spark plugs, wires, cover for the distributer,rotor arm and so on. Also new fuel filter, fuel pump and pipes and hoses, new pressure regulator, air filter, idle valve, new boot for intake + hoses, new tube of death on the intake to the block with dealings, and new gaskets for intake manifold. So MANY money spend on this motor, but after some time driving the car, I suddenly feel the car hesitates and loses power, like the engine cuts out shortly and then comes to live again. I tried to figure out if there was a pattern when engine does that, but the only thing I figured out was that when the engine is completely cold it will drive perfectly the first 2-3 minutes and then do as I wrote earlier. Some days later, after the engine got warm and it began to cut out while driving, I stopped and while the engine running I pulled out wiring for the air flow meter, and of course the engine shut off. I then started the engine again and drove and I realized that it drove perfect again. I tried this many times to confirm and yes, every time I do it it will drive perfect for about 10 minutes max and then troubles again. I tried with another air flow meter, and exactly the same happened if not worse. So I began suspect the engine management ECU, and I replaced this, but the same thing happened.
    So now I know for sure something electronic is wrong I think, but can't do much diagnostics on this old m20, so I need your help diagnosing. I live in Denmark by the way so this is an Euro car.

  2. #2
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    When the engine cuts out, does the tach immediately dive for 0? This would indicate an ECU issue as it shows that the ECU is no longer even trying to signal a spark. Since you replaced the ECU itself, it's not likely that. I'd suspect the main relay or crank sensor. If the tach does not immediately drop, it shows you're getting spark. I'd then be looking at a fuel issue. It could be the relay, pump or sediment in the tank getting stirred up and blocking the inlet.
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  3. #3
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    1987 BMW E30 320i Coupe
    The tach does not drop at all, so I would also think that the ECU are giving it spark. When I rebuild the motor, I also replaced the main relay and fuel relay in the engine bay. So these are also not the issue.
    Could it be crank sensor? On this old motor it has two sensors mounted on the gearbox, but I remember also checking the resistance on them and they were in spec. And the engine is turning over and starting right up both when it is hot or cold so I don't think the sensors are defective.
    Like I wrote, I replaced the iron lines for the petrol under the car from tank to motor, and replaced all fuel hoses, and replaced new fuel pump from bosch, and new fuel filter and so on. And it is holding pressure. So I don't even think that there is a problem there.
    I think that what I am experiencing when removing the wires to the air flow meter and reconnecting them, I am restarting the ECU, and it will drive normally, until the engine gets a false reading from something or some sensor, so it triggers the engine into safe mode or something like this, and this is maybe what I am experiencing? Can someone verify this please?

  4. #4
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    Hello. I know this is old but my car has recently started doing the same thing but only when I snap on the throttle to accelerate when passing or taking off. I replace just about all the same within a year. New crank sensor, ecu, and fuel/ign parts. It only does it I noticed when I'm driving it for about 30-40min. I tried a different cone filter and it helped but still does it. Im gona try the stock box agian and see if it stops but if that doesn't fix it I have no clue. Motor is at about 130k. It's the new m20. Any help is appreciated!

  5. #5
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    1990 BMW 325is Coupe
    Quote Originally Posted by Edirty199 View Post
    Hello. I know this is old but my car has recently started doing the same thing but only when I snap on the throttle to accelerate when passing or taking off. I replace just about all the same within a year. New crank sensor, ecu, and fuel/ign parts. It only does it I noticed when I'm driving it for about 30-40min. I tried a different cone filter and it helped but still does it. Im gona try the stock box agian and see if it stops but if that doesn't fix it I have no clue. Motor is at about 130k. It's the new m20. Any help is appreciated!
    Same issue... motor runs great for 20 mins and then cuts out. I have changed every sensor except the throttle position sensor. Chased down all of my vacuum issues. Fuel pressure looks good at about 2.5 bar at idle. The fuel pressure does not drop when the engine cuts out. My motor stumbles and then totally dies. Tach goes to zero and dead as a door nail.

  6. #6
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    1998 BMW e36 328i
    Any news on this one ?
    Yesterday I drove my 1997 325 auto, for about 20 minutes and the engine died, but started right up, I got on the highway, and drove 2-3 exists and the car tried to die a few times, I took the off ramp and it died there, but started right back. Drove it home for 10 minutes through the city, ran fine, this morning is running fine. Kinda scared to drive too far now.
    What could be? I can't diagnos because it's running great now

  7. #7
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    No e30s, again :(
    Yours is alot newer so i am not sure how many e30 people can help. Try asking in the e36 section
    No e30s again.

  8. #8
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    Quote Originally Posted by cerber717 View Post
    Any news on this one ?
    Yesterday I drove my 1997 325 auto, for about 20 minutes and the engine died, but started right up, I got on the highway, and drove 2-3 exists and the car tried to die a few times, I took the off ramp and it died there, but started right back. Drove it home for 10 minutes through the city, ran fine, this morning is running fine.
    My guess would be junk in the fuel tank. Local driving doesn't put much of a demand on fuel volume, interstate / higher speed does. When the car shuts off, the junk drops from the in tank pick up sock. Pull the in-tank pump and take a look.
    2004 525i Sport, Manual - 1985 325E Coupe Manual

  9. #9
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    No e30s, again :(
    I remember reading that as a big problem on the newer cars, lots of guys had that trouble.
    No e30s again.

  10. #10
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    Quote Originally Posted by richardodn View Post
    When the engine cuts out, does the tach immediately dive for 0? This would indicate an ECU issue as it shows that the ECU is no longer even trying to signal a spark. Since you replaced the ECU itself, it's not likely that. I'd suspect the main relay or crank sensor. If the tach does not immediately drop, it shows you're getting spark. I'd then be looking at a fuel issue. It could be the relay, pump or sediment in the tank getting stirred up and blocking the inlet.
    See Richard's post = did you change the main relay? I did have a similar issue this summer car randomly would misfire and cut off because the main relay was shorting out or going bad.

    It is kinda scary..

  11. #11
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    Quote Originally Posted by cerber717 View Post
    Any news on this one ?
    Yesterday I drove my 1997 325 auto, for about 20 minutes and the engine died, but started right up, I got on the highway, and drove 2-3 exists and the car tried to die a few times, I took the off ramp and it died there, but started right back. Drove it home for 10 minutes through the city, ran fine, this morning is running fine. Kinda scared to drive too far now.
    What could be? I can't diagnos because it's running great now
    I know I may be asking a really stupid question here but just to make sure I understand, when you say that the engine starts right up, do you mean it starts right up when you turn the key in the ignition, and not that it starts right up on its own, correct?

    If so, I'm having the same problem with my 1987 325e. I already changed spark plugs, ignition wires, distributor, rotor and main relay.

  12. #12
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    I'm far from being an expert on this stuff but have owned my 87 325is for more than 20 years and something like this happened to me....sometimes it's the dumbest little things that are the most frustrating. Anyway, it turned out to be an intermittent code relay. The OBC has that security feature where you can set it up so you have to put in a code or the car won't start; most people don't use it any longer, but the code relay (located in the dash above the steering column) can short out/go intermittent and shuts your car off. When I found that, I just bypassed it by hardwiring the input & output from that relay box...problem gone.

  13. #13
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    Quote Originally Posted by Max87IS View Post
    I'm far from being an expert on this stuff but have owned my 87 325is for more than 20 years and something like this happened to me....sometimes it's the dumbest little things that are the most frustrating. Anyway, it turned out to be an intermittent code relay. The OBC has that security feature where you can set it up so you have to put in a code or the car won't start; most people don't use it any longer, but the code relay (located in the dash above the steering column) can short out/go intermittent and shuts your car off. When I found that, I just bypassed it by hardwiring the input & output from that relay box...problem gone.
    I wonder if that would possibly be my problem. Do you have a part number? I could not find anything on pelican parts or the bentley manual. Could you also describe the problem you had a little more? Would the engine just shutoff while driving the car?

  14. #14
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    Quote Originally Posted by Max87IS View Post
    I'm far from being an expert on this stuff but have owned my 87 325is for more than 20 years and something like this happened to me....sometimes it's the dumbest little things that are the most frustrating. Anyway, it turned out to be an intermittent code relay. The OBC has that security feature where you can set it up so you have to put in a code or the car won't start; most people don't use it any longer, but the code relay (located in the dash above the steering column) can short out/go intermittent and shuts your car off. When I found that, I just bypassed it by hardwiring the input & output from that relay box...problem gone.
    Could you elaborate more on this? I’m going through the same thing and Rich has been trying to help me through it but at the moment it’s literally a needle in the haystack. I’m about to lose all motivation I don’t want to though. It runs and starts just fine and once it’s been running and the whole system is at full heat it shuts down randomly. I’ve used my last free tow to take it home and I really don’t want to move it anymore idk what to do

  15. #15
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    man it sounds like something electronic is overheating and crashing. i had a similar issue but it turned out to be bad fuel pumps and a fuel tank that was beyond saving. Replaced both and it seemed to fix the problem. I have heard on other vehicles the coil getting hot and losing the spark. You could try replacing the coil.
    1987 BMW 325i Convertible


    “Speed has never killed anyone, suddenly becoming stationary… that’s what gets you.”
    Jeremy Clarkson


  16. #16
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    Quote Originally Posted by doctorx69 View Post
    man it sounds like something electronic is overheating and crashing. i had a similar issue but it turned out to be bad fuel pumps and a fuel tank that was beyond saving. Replaced both and it seemed to fix the problem. I have heard on other vehicles the coil getting hot and losing the spark. You could try replacing the coil.
    Do you know what specs/amps the coil should be running with the engine running/key in ACC? The coils really never something I’ve looked at and it’s I’m sure 33 years old like the rest of the car

  17. #17
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    Table b. Ignition Coil Resistance
    TEST Engine Terminals Resistance
    Primary resistance 4-cylinder 1 ( - ) and 1 5 (+) .82 ohms
    6-cylinder 1 ( - ) and 15 (+) .50 ohms
    Secondary resistance 4-cylinder 1 ( - ) and 4 (center tower) 8250 ohms
    6-cylinder 4 (center tower) and 1 5 ( + ) 5000 ohms
    1987 BMW 325i Convertible


    “Speed has never killed anyone, suddenly becoming stationary… that’s what gets you.”
    Jeremy Clarkson


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