914-SHO CCRM diodes?

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by 3d914, Dec 14, 2012.

  1. 3d914

    3d914 SHO Member

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    In the searches I've done, I can only find a wiring diagram for the ATX CCRM, even though I'm building a custom CCRM to replace the MTX CCRM. That leaves me guessing as to the differences between the two - especially the use & placement of diodes.

    1. Are the diodes used for reverse-voltage protection only?
    2. Can I eliminate the Voltage inverter relay and it's corresponding diode?

    [​IMG]

    TIA
     
  2. Shovert

    Shovert Active Member

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    Here is a 91 diagram of SHO. Unsure of year computer you are using. I found I could change year in link and get differant SHO diagrams. Decent diagram of IRCM. A thought do you have access to a 3.0 IRCM even a bad one. That way you fiqure out the internal wiring. My thoughts. Maurice
    I know Russian site so far my Advast anti-virus program has not kicked on it.
    http://taurus-club.ru/manuals/Ford_Taurus_1991_wiring.pdf
    Edit page 28 is the 3.0 SHO diagram for the IRCM
    Edit Here is site on the IRCM Basic info. [This not for the SHO so wiring is not same] but gives insite into operation.
    http://jrthecar.com/articles/ircm/index.html
     
    Last edited: Dec 14, 2012
  3. Off Road SHO

    Off Road SHO Moderator Staff Member

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    Why are you doing all that? Do you need all those things that are in the CCRM?

    Tom
     
  4. 3d914

    3d914 SHO Member

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    Thanks Maurice, been through the russian site - still no internal wiring diagram for the 95 MTX (3.0L - XJ2 PCM) CCRM.
     
  5. 3d914

    3d914 SHO Member

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    Tom,

    Yes, I need relays for FP, PCM power, Low & High fan, and A/C (later). In my custom relay diagram I omitted the Voltage inverter relay, and in my installation I left out the A/C relay for the bench test.

    All the wiring is checking out except for some weird crossing of circuits (see post here). I suspect its because of some reverse voltage issues. This is why I'm trying to understand their usage of diodes in the stock ATX CCRM.
     
  6. Shovert

    Shovert Active Member

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    A thought can you install a CCRM? I call it IRCM. Maybe install it and see if runs and does ok. Then once get it going go from there how to wire you custom relay. Just a thought. Maurice
     
  7. 3d914

    3d914 SHO Member

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    Maurice, yes I've considered that - especially since it looks like I need most of the relays in there. I just thought it would be nice to get away from this specialized, unserviceable component.

    But if I get one and it later fails, then I'll have one I can tear apart and make a schematic of. Good idea Maurice.

    I'd still like to know what the diodes do though.
     
  8. Shovert

    Shovert Active Member

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    I agree. A thought and I have no base to form this thought. Maybe diodes keep the computer from seeing problems when there is none because of interconnection at the the CCRM? Maybe idea maybe real stupid one. Maurice
     
  9. shoon

    shoon cliTaurus

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    When you collapse the magnetic field of a relay coil (remove power from it), it will reverse the voltage polarity. The diodes are there strictly to protect against a spike in reverse voltage. Likely the diodes are in place to protect the ECM.

    Quenching Diodes:
    Anytime that a relay coil is driven by a circuit that is not specifically designed to drive a relay, you should use a quenching/suppression diode connected in parallel with the relay coil. The diagram below will show the connection of the diode. Initially, you may think the diode serves no purpose because the voltage applied to the relay cannot pass through the diode. This is true when the relay is energized. The diode comes into play when the power source is removed from the relay coil. When power is applied to the relay coil, a magnetic field is created and energy is stored in the coil. When power is removed, the magnetic field collapses causing a reverse voltage to be generated (it's called inductive kickback or back EMF). The back EMF can easily reach 200 volts. The diode will absorb the reverse voltage spike. This voltage, if not absorbed by the diode, will cause premature failure of switch contacts and may cause the failure of power switching transistors. You can use virtually any type of rectifier or switching diode (i.e. 1N4001, 1N4002, 1N400x... or Radio Shack part #s 276-1101, 276-1102, 276-1103, 276-1104).

    A simple explanation on it can be found here:
    http://www.bcae1.com/relays.htm
     
    Last edited: Dec 15, 2012
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  10. Shovert

    Shovert Active Member

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    I understood relays etc. I have done wiring for over 40 years. But learned something today. Thanks alot. Makes sense. Thanks for posting. Maurice
     
  11. 3d914

    3d914 SHO Member

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    After looking at this, though, I'm not sure its the same application for the ICRM/CCRM as their diodes are not in parallel with the coils, but appear to be limiting voltage flow/direction.

    What's confusing though is the behavior surrounding the hi-side of the EDF Relay (Low fan). Notice that the low side of the relay never seems to go to ground. It either drives the low side of the voltage inverter or feed back into its own high-side, along with the power coming from the output side of the PCM power relay. This just doesn't make sense to me. Keep in mind though - I'm assuming the voltage inverter is in fact a relay. It may instead be some sort of solid-state device that has different input/output.

    [​IMG]
     

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