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Thread: M50 coils, main relay or fuel pump relay?

  1. #1
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    Default M50 coils, main relay or fuel pump relay?

    When do the coils get their +12v? Is it when the fuel pump relay clicks over or the main relay clicks over? I am wanting to make sure that they come on when the fuel pump relay clicks over because I don't want to have my coils loading if the car isn't running else pop pop pop

  2. #2
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    Default When key is turned into run or start.

    But I don't see your point!

    Javier

  3. #3
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    Default

    they power up off the main, they still don't do anything till the computer triggers them
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  4. #4
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    The coils remain ungrounded until its time for them to start making spark. They won't "load up" until they are grounded by the ECU, and that won't happen until it sees an RPM signal.

  5. #5
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    Default Let me rephrase to make it clear. ...

    12+ is received from ignition key, not the main relay, nor the pump relay. Main relay feeds, besides ECU, injectors, pump relay, oxygen sensor relay, evaporative purge valve, ICV, EGS, and MAF.

    I do agree that having 12 Vdc at one pin of the primary coil does nothing until you get the other pin grounded (unless you have coil issues), that won't happen until ECU decides to do so. Not sure about your special retrofitted ECU, but guess it won't either fire the coils until you get a sync. signal from CPS.

    When the cars were build with distributors and contacts, yes you could be in trouble keeping ignition key turned on for long time if the contacts were closed (that happens in more than 50% of the distribution rotation). You may be too young to remember those times! (just kidding).

    Javier
    Last edited by Javier; 05-30-2006 at 02:52 PM.

  6. #6
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    Quote Originally Posted by Rustam
    I think he is seeking to understand where the potential difference across the primary comes from. He can not find the schematics to be enough...

    Bite me - you have no idea what I am trying to do.


    There are NUMEROUS conflicting wiring diagrams floating around - you think I haven't checked it out? Sigh. Stay out of my threads.


    by the way:

    Rustam has just replied to a thread you have subscribed to entitled - M50 coils, main relay or fuel pump relay? - in the 5 Series BMW forum of Bimmer.Info Forums.

    This thread is located at:
    http://www.bimmer.info/forum/showthr...6&goto=newpost

    Here is the message that has just been posted:
    ***************
    How about looking at the wiring there Jon?

    And he calls me "ridiculous"...
    Pathetic.
    ***************


    No - you're ridiculous, and pathetic.

  7. #7
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    Quote Originally Posted by Javier
    12+ is received from ignition key, not the main relay, nor the pump relay. Main relay feeds, besides ECU, injectors, pump relay, oxygen sensor relay, evaporative purge valve, ICV, EGS, and MAF.

    I do agree that having 12 Vdc at one pin of the primary coil does nothing until you get the other pin grounded (unless you have coil issues), that won't happen until ECU decides to do so. Not sure about your special retrofitted ECU, but guess it won't either fire the coils until you get a sync. signal from CPS.

    When the cars were build with distributors and contacts, yes you could be in trouble keeping ignition key turned on for long time if the contacts were closed (that happens in more than 50% of the distribution rotation). You may be too young to remember those times! (just kidding).

    Javier
    That's exactly what I needed to rule out Javier - I am reading MUCH literature and finding that the aftermarket ECUs insist to use the fuel pump relay as a +12v source for the "coil". However, I have multiple coils and a completely different circuit than distributed cars, and so I was given a warning by another MS user to isolate the coil +12v from the rest of the car by using fuel pump so as not to burn it up if ign key is left "ON". I thought to myself well, this doesn't happen with OE system so... and I wanted to make sure. I have about 3 diagrams saying the 12v comes from various sources... I'd rather ask the EXPERTS (thanks javier, no thanks Crustam) what their thoughts were on it.

  8. #8
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    Default About the mod you are proposing. ...

    I'm not sure it will be fine, I meant switching the 12V supply to the coils from the key to the pump relay. The pump relay gets a priming pulse when you turn key on, and then stops waiting for CPS/ECU to turn it back on. I don't know details on the criteria to turn it back on. If it requires a minimum rpm that is only achieved when firing gets in, you will end with a non starting engine.

    Best solution is to check for this. The coil supply line is a green wire coming from the key switch, and going to all the coils together and the ECU pin 56. You need to keep the feeding to the ECU from the key, so can loose the green wire at splice X6831 (when all coil green wires mets together), and substitute for a wire from fuse F23 (Feed side, by the way coils are unfused). Test for proper starting. You can select to avoid permanent wiring damage testing the pump relay for kick in wile cranking the car without the coils connected. If cranking speed is enough for pump to be energized (sorry I doubt it), you will be fine making the mod. If not, this will confirm my suspicion that if the engine does not kick in, the pump is not energized. May be Bill R. can tell us about the criteria.

    If there is a recommendation to control the 12V supply to the coils, may mean that aftermarket ECU is grounding the coils as a steady state condition wile the engine is not running (like old distribution cars). Bad indeed!

    Javier

    Edit: By the way, may be the aftermarket ECU criteria to turn the pump back on is different to DME, and do it as soon as it sees CPS pulses, them permitting the coils connected to the pump relay to fire up the engine.
    Last edited by Javier; 05-31-2006 at 04:47 AM.

  9. #9
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    Default

    Quote Originally Posted by Jon K
    That's exactly what I needed to rule out Javier - I am reading MUCH literature and finding that the aftermarket ECUs insist to use the fuel pump relay as a +12v source for the "coil". However, I have multiple coils and a completely different circuit than distributed cars, and so I was given a warning by another MS user to isolate the coil +12v from the rest of the car by using fuel pump so as not to burn it up if ign key is left "ON". I thought to myself well, this doesn't happen with OE system so... and I wanted to make sure. I have about 3 diagrams saying the 12v comes from various sources... I'd rather ask the EXPERTS (thanks javier, no thanks Crustam) what their thoughts were on it.
    Re aftermarket ecu's:

    Jon I've done quite a few retrofits of some common programable 3D (fuel/ignition) ecu's such as Microtech, Wolf and Greddy. Most of my setups have consisted of retrofitting direct fire coils to cars that had used traditional distributors.

    My take is the following:

    All of them use thier main relay (usually fuel pump) for the +12v feed to the coils (they all switch the coils on or off by the transistors switching 'on' and grounding the -12v side of the coil). This is a safety feature that allows you to pull one relay to isolate all the engine electrics if needed.

    All coils are earth (-) switched be it by points (kettering) or electronic (transistor) ignition system, this reduces the load (amps) handled by the switch.

    In the days of points (kettering) systems if you left the ignition on with the engine off you could burnout the capacitor (used to stop the points from arcing, increasing their service interval) or burn out the primary winding in the coil. most cars had a resistor in line with the coil that dropped the voltage going into the coil to around 8 volts, this reduced the risk of coil frying but didn't stop it all together.

    But fear not those days are well gone now!

    In a computerised system things are very different, the coils aren't triggered (grounded) by the ecu unless the ecu receives a valid rpm input from the crank (or cam) angle sensor.

    So basically even though there is power to the coils the circut is incomplete (not grounded by the switching transistors in the ecu). Once the engine is cranked over the C.A.S. signal tells the ecu to switch the ignition transistors 'on' (to ground) in the correct order at the correct time (using the ecu's ignition / rpm map).

    If the engine is not rotating the ecu DOES NOT receive any crank trigger reference or rpm signal, therefore the ignition transistors will be 'off' (open circuit) and the coils will not be 'charged' by the ignition system.

    Logic tell us that if a switch is 'off' no current flows.

    HTH

    Ross
    BMW parts professional

    Previous rides:
    BMW
    E12 M535i (go the dogleg!)
    E28 M535i (MMM M88!)
    E34 535i M

    MAZDA:
    RX7 S-IV T04 (440 hp ATW)
    RX7 S-I 13b bridge port
    RX4 13b peripheral port

  10. #10
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    Default

    As a follow up to Javier's post, I am 99% sure it is only rpm signal that is used to keep the fuel pump active. I think the only other criteria for fuel shut down is airbag deployment.

    Either way, since the coils are powered by the ignition, the real concern is whether the aftermarket ECU grounds the coils with no rpm reference or not. If the new ECU does not ground the coils with no RPM signal, then just leave coil power supply stock and ignore any instructions for powering the coils. If the ECU does ground the coils with no RPM signal, then maybe just wire in a separate relay that will come on in the manner you find most pleasing.

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