E36 M3 3.0 Wont start!! Suspected DME... advice needed please

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  1. E36 M3 3.0 Wont start!! Suspected DME... advice needed please 
    #1
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    A friend had stored their E36 M3 3.0 with me for month or so and I went to start it today. It cranks over fine but wont start. The owner says it used to do this but only intermittently and always started on the second or third go.

    Here is what I know...

    There is no spark and the fuel pump isn't running, neither when you turn the ignition on or when you crank the engine.

    The fuel pump itself is working, verified by powering it directly from the fuse. Crank sensor has now been swapped with one from a running car and it isn't that.


    Main relay has been bench tested, its fine. Also checked all four small relays either side of the main one, as I think one or more of them are for the fuel pump. They are fine and power is present where it should for these relays.... its just there is no signal being sent to the main under ignition on or cranking and there should as far as I understand.

    It seems the DME/ECU sends a ground signal to complete the circuit at the main relay thus allowing power to flow through the main relay to the fuel pump relays etc. This is not happening!

    I have checked what pin on the DME/ECU this signal is sent from (27) and done a continuity test between that and the relevant terminal of the main relay. This is fine too!

    So I am assuming the ERM is for what ever reason not sending this earth signal to the main relay. It could be related to the EWS 2 but i dint think it would crank if it was an EWS problem?

    I looked at the DME/ECU and it looked like it had been opened before as some of the tabs were snapped off and pry marks were present. Ive opened it up and had a look, seems to have some marks that could have been water that dried on the aluminium case. Did a long and careful inspection of the circuit boards for any burn marks or evidence of a short.

    No sign of anything obvious, i did clean the boards with some mild contact cleaner and a cotton bud, dried it using warm air a gun and left it for few hours before reassembling. I dint expect it to help....and unfortunately it dint!

    Either its a faulty ECU or it isnt getting what it needs to deliver the signal(s)...any ideas where to go from here would be greatly appreciated

    At this point I could replace the ECU but I know there is some issues with the coding for the EWS unit. Can someone tell me what needs to be done to replace an ECU ?

    Thanks in advance!
    Last edited by ArcEye; 13-09-2011 at 00:35.
     
     

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    ERM=ECU?
    You can swap them to a non EWS one, which will have an coloured bosch label, the EWS ones have a silver sticker with black text (i think the 075 is mostly a black sticker)

    Cranking means EWS box is happy with the key.
    You are right about the general electrics, the ECU has a permanent live, a switched live from the ignition, and it then switches on it's own Main relay for proper power.
     
     

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    Quote Originally Posted by TheEnd View Post
    ERM=ECU?
    You can swap them to a non EWS one, which will have an coloured bosch label, the EWS ones have a silver sticker with black text (i think the 075 is mostly a black sticker)

    Cranking means EWS box is happy with the key.
    You are right about the general electrics, the ECU has a permanent live, a switched live from the ignition, and it then switches on it's own Main relay for proper power.
    Sorry! Yes I meant to write DME (ECU) not erm, dont know where that came fromlol , shame i cant edit the title...

    So will a non ews ecu just plug and play ?Ie with the original key etc?

    Also is it worth checking the pins on the ecu loom for a constant and switched live? Cant remember the pin number can you?

    What are the signs of a dead ecu?
     
     

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    Any non EWS ecu would plug straight in and fire up without having to do anything else.

    Permanent power is on pin 26, 27 is the output to switch the DME Relay on, 54 is where the power from the DME Relay comes in, and 56 is the "ignition on" input.
     
     

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    My firends 3.0 M3 done this, cranked but wouldn't start. He thought it was the starter, put a new one on and still no luck.

    Long story short he got under the car one day and found one of the fat earthing cable from the block had disconnected itself, reconnected it and she fired up first time.

    I have no knowledge of car electronics and sounds like you're pretty clued up but could be worth a check that everythings earthed correctly.
     
     

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    ArcEye (13-09-2011)

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    Quote Originally Posted by TheEnd View Post
    Cranking means EWS box is happy with the key.
    And what if the EWS unit and ECU aren't happy with each other ?
    I thought the engine would still crank, but won't fire.... Or is this the case when it'll fire up for a second or two then die again ?

    To the OP - It might be worth using a jump cable to create your own earth from engine to body to see if that helps.
     
     

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    ArcEye (13-09-2011)

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    Quote Originally Posted by Ferret View Post
    And what if the EWS unit and ECU aren't happy with each other ?
    I thought the engine would still crank, but won't fire.... Or is this the case when it'll fire up for a second or two then die again ?

    To the OP - It might be worth using a jump cable to create your own earth from engine to body to see if that helps.
    The 3.2 would fire and die, not sure abut how the 3.0 reacts, but despite the immobiliser often being blamed quickly, unless the ECU has been swapped, it should still be fine.
    ie. there shouldn't be any way for it to slip out of sync with the ECU.
     
     

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    Hi thanks for everyone's quick and helpful replies...

    I have checked the engine to body earth strap and this is secured, confirmed its ok by doing a continuity test between the body and engine in a few places... I have heard that can be a problem as well, was definitely worth checking.

    I have checked for a constant live and ignition live at the appropriate pins, many thanks for the pin numbers ...these both seem to be fine and as should be. There is just no earth signal from the ecu to main relay.

    I tried faking the signal by connecting a ground to the main relay itself, it seems to switch it on and something on the engine starts to buzz...is this the coil packs possibly? However no sound of a the fuel pump when i do this.

    I did try starting quickly but no joy. I then left that earth to main relay connected and i gave fuel pump fuse power, which does make the pump operate. Again nothing.

    Are there anyway of getting the ECU tested? I see the non ews ones are alot more expensive for obvious reasons I guess. Does anyone have a good source for a new ecu? Its looking more like that's going to have to be swapped now...running out of ideas.

    Thanks for the assistance so far, I shall update if i find anything in the mean time.
     
     

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    You could get an ECU with EWS, but you'll need the EWS control box and a transponder from inside the key as well.
     
     

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    Quote Originally Posted by Ferret View Post
    You could get an ECU with EWS, but you'll need the EWS control box and a transponder from inside the key as well.
    Yea that seems to be the slightly cheaper option, I would probably go for a non ews ECU to avoid any potential issues with ews down the line...is there a sure fire way that I could find out if the ECU i f have is faulty?
     
     

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