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Thread: Another Classic 'My Car Doesn't Start' Thread

  1. #1
    Join Date
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    1986 BMW 325es Coupe

    Another Classic 'My Car Doesn't Start' Thread

    Believe me, I've used the search function haha.
    Car is a US model 1986 325es manual coupe
    Here's what I know:
    Car cranks fine
    Fuel pressure up to the fuel rail when relay is bypassed
    I only get spark for a split second after turning the key off when cranking (ie no spark when cranking but a little spark once stop trying to crank)
    DME is not getting power
    Main relay and fuel pump relay are not getting power
    Bypassing the fuel pump relay engages the fuel pump but bypassing the main relay does nothing
    All other electrics work, dash lights, radio, headlights, power windows, etc
    I have heard that the OBC can cause this kind of issue so i bypassed it by bridging the green and green/red wires going to the obc relay (obc still turns on) same issue
    Occasionally the car will have tach movement when cranking but not every time (this persists with new CPS)
    I checked and the reference pin is intact

  2. #2
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    E21 323i, E36 M3
    Have you looked at this guide yet?


  3. #3
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    Quote Originally Posted by hotdish View Post
    Have you looked at this guide yet?
    Just did, it's pointing me to the ignition switch which I admittedly should have checked before. I have not actually seen this guide before in any of the numerous sessions of googling. Thank you. Tomorrow I will check to see if power is coming from that switch and update. Do you think that the switch is bad or is it more likely that there is a short somewhere seeing as the accessories all work?

  4. #4
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    No e30s, again :(
    only one way to tell
    No e30s again.

  5. #5
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    Quote Originally Posted by SlowE30eta View Post
    Do you think that the switch is bad or is it more likely that there is a short somewhere seeing as the accessories all work?
    Could be a bad ground too, you're going to have to keep checking wires.


  6. #6
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    Ok so I tested some things today. The grounds on the DME are good. Seems there is a lack of connection between the main relay and the DME. Could be just a frayed wire or it's grounding somewhere on the way there. Is there any easy way to give the DME power manually ie with a switch? Aside from pulling apart the harness and cutting the right wire.

  7. #7
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    Update: I gave power to the DME directly by cutting the loom and giving power to the two blue/red wires of pin 18 and 35.
    I'm guessing it is a bad ignition switch.
    I noticed the loom has been touched before me, hopefully just to install the awful looking aftermarket head unit.
    Anyway the injectors are firing now but still no spark. The coil has power but does not have the necessary ground pulses. There is continuity between the coil ground and pin 1 on the DME which is the ignition timing pin. In addition I pulled apart the DME and noticed it has been opened before and has a Conforti chip from 2002. Somewhere in there the tach stop working (I think it was when I was messing with the CPS).
    My conclusion is that either the CPS is dead/plugged in wrong/switched with the Cylinder ID sensor or the DME has crapped out. I've tried searching for a way to test the DME and it appears there is none. Tomorrow I will try to see if I can get a tach again and see if that fixes it to hopefully rule out the CPS.

  8. #8
    Join Date
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    Today's update,
    I believe the CPS is the only thing I am missing now. Tried swapping it out with a new one, swapping it with the Cylinder ID sensor and swapping the connectors. I am unsure as to which connector is for the CPS, there is a grey one and a black one. Still no tach. I will check further for continuity tomorrow.
    Also I noticed all three of the sensors I have have the same part number 18810.
    I was under the impression that the Cylinder ID sensor is a different sensor (I remember reading it was a different length). It seems at some point before me someone put a CPS in the Cylinder ID slot. I have no idea why.

  9. #9
    Join Date
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    No e30s, again :(
    they are the same for your year eta. I forget which goes in which hole but you check resistance on them to see if they are good, if I remember.
    No e30s again.

  10. #10
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    Quote Originally Posted by SlowE30eta View Post
    I've tried searching for a way to test the DME and it appears there is none.
    The usual suggestion is to try a known good one, but you can at least pull the cover off and see if anything looks fried.


  11. #11
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    Pulled the cover off, nothing seems obviously fried. The outside of the cover has a surprising amount of corrosion on it.

  12. #12
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    Ok so here's the update.
    Figured out which plug it is. It's the light grey one.
    Two of the plugs pins go directly to the DME, the other one I don't know. I haven't been able to find it on any wiring diagrams. It is not getting power and it is not being a ground. I am unsure of what it is supposed to be.
    According to a wiring diagram I was looking at the tach is fed by the pulsed ground on the coil. Is this accurate? It would make sense if it's not sending a ground that the tach isn't working.

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