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Thread: Critique my wiring diagram - source of EMI?

  1. #1
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    Default Critique my wiring diagram - source of EMI?

    I think I may have some noisiness in my ECU wiring, but I'm not 100% sure. A picture is worth a thousand words, so here's a picture of my crudely drawn wiring diagram. I hope it's legible. This reflects my wiring today.
    I'm not sure about my connection from Side A of the ballast resistor to the pink trigger wire from the Sniper. The manual clearly says that it shouldn't be connected to "dirty sources like the coil" and I sort of have that situation, just on opposite sides of the ballast resistor. I'm also not sure about having the pink ECU trigger wire directly connected to the + side of the Pertronix ignition unit (NOT on opposite sides of the ballast resistor).

    Looking at the wiring diagram online for the Pertronix unit, it looks like I should have that + wire on the opposite side of the ballast resistor, but I don't know if that will change anything. When I originally did the wiring, I was somehow thinking that having the ballast resistor between the + coil terminal and the pink ECU trigger would somehow prevent the noise issue. Dumb? Don't worry about hurting my feelings, LOL. I don't have another obvious place to connect the pink ECU trigger wire on my car. Have not found any other wires that are hot during cranking and key in the run position. Do I need to rig up a new circuit with a relay? And if so, connected to WHAT?


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  2. #2

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    There's not a place in your fuse box like and IGN post? Either way, yes, it's highly recommended that you connect the pink trigger wires to a relay that gets its main power directly from the battery. For the switched side of the relay, you can use a toggle switch or one of the points in your diagram. By having that source only trigger the switch side of the relay it will be fine.

  3. Default

    RFI/EMI could be affecting other areas of the installation, not just the areas marked up. Perform a few searches on the forum for RFI, EMI, Noise, etc. There are other posts they may help reveal what to look into. Additionally, Chris has a good read up here: https://www.efisystempro.com/efi-pro...r-rfi-problems
    1970 XW Fairmont (presented as a GT Falcon Replica), 351 Cleveland with Aussie 302 2V closed chamber heads. Edelbrock F351 2V dual plane intake manifold. Camtech CT21544 (234/238@050", 570/579lift, 2600-6200rpm quoted range, 110lobes) 1.73:1 roller rockers. AOD Transmission. Ford 9" 3.5 Diff ratio. Pacemaker #PH4050 2v Tri-Y extractors to 2.5" Hi Flow V-Tex merge pipe with dual 2.5" exhaust through Hooker Aero Chamber Mufflers. Holley Sniper EFI 4150 Super Sniper 650 with HyperSpark Ignition.

  4. #4
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    Quote Originally Posted by XW_Falcon_351C View Post
    RFI/EMI could be affecting other areas of the installation, not just the areas marked up. Perform a few searches on the forum for RFI, EMI, Noise, etc. There are other posts they may help reveal what to look into. Additionally, Chris has a good read up here: https://www.efisystempro.com/efi-pro...r-rfi-problems
    That link is OUTSTANDING! Thanks for sharing.

    Quote Originally Posted by gregs69rs View Post
    There's not a place in your fuse box like and IGN post? Either way, yes, it's highly recommended that you connect the pink trigger wires to a relay that gets its main power directly from the battery. For the switched side of the relay, you can use a toggle switch or one of the points in your diagram. By having that source only trigger the switch side of the relay it will be fine.
    Nope, nothing in my fuse box appears to be linked to the ignition. I think I'm going to go the relay route to be safe.

  5. #5
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    The pink 12 volt wire should not be run to the ballast resistor wire, a HEI source, or a even worse to the ignition coil positive. These are dirty sources. You need a clean source such as directly to the ignition switch or a relay. The easiest spot to hook up the pink 12 volt wire is in fact the ignition switch. A datalog will confirm if you do in fact have EMI.
    Last edited by RPnova; 07-16-2019 at 01:20 PM.

  6. #6
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    Quote Originally Posted by RPnova View Post
    You need a clean source such as directly to the ignition switch or a relay. The easiest spot to hook up the pink 12 volt wire is in fact the ignition switch.
    Thank you!

    Originally Posted by Danny Cabral
    Ensure the Switched +12V red/white wire (pink wire - Sniper EFI) is powered in the "Run" and "Crank" key positions.
    The ignition switch must have a wire that's powered in "run" and "crank" key positions leading to the ignition system.
    The ignition switch can't start the engine, if there isn't a circuit that's powered in the "Run" and "Crank" key positions.
    The easiest way to find this wire, is to look at the wiring schematics in a factory shop manual or even a Haynes manual.
    https://www.msdperformance.com/suppo...s/#EngineRunOn (MSD Troubleshooting - Engine Run-On)
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  7. #7
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    Quote Originally Posted by RPnova View Post
    The pink 12 volt wire should not be run to the ballast resistor wire, a HEI source, or a even worse to the ignition coil positive. These are dirty sources. You need a clean source such as directly to the ignition switch or a relay. The easiest spot to hook up the pink 12 volt wire is in fact the ignition switch. A datalog will confirm if you do in fact have EMI.
    Running a clean source directly from the ignition switch is exactly what I've been trying to do and that's where I'm getting confused. From my ignition switch (1966 Corvette), there's only one wire terminal that is hot in both "cranking" & "run" positions, and that terminal is connected to a wire that runs directly to the ballast resistor. That same terminal has a second wire connected to it that runs elsewhere (can't remember from the wiring diagram), but it's still 100% electrically connected to the wire headed to the ballast resistor. Am I missing something really obvious here?

  8. #8

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    I think what others are trying to tell you what to do, may not be described clearly.
    An automotive 4-pin relay is what you need. These are very common, no I don't have a link to one, but if you Google it you should find a lot of images for them. The relay has a small coil of wire inside of it that closes heavy duty contacts when +12V is applied to it. You hook your wire coming from your ignition key to terminal 86 on relay. You hook terminal 85 to ground. You run a wire straight from the battery to terminal 30 on the relay and hook the wire going to the Sniper's pink wire to terminal 87.
    When you turn on the ignition key it sends a signal to the relay and the relay closes which then connects the battery straight to the pink wire. Here's a generic video showing the operation of a relay:
    https://www.youtube.com/watch?v=Mru8BbTGDwMI

  9. #9
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    Thanks for the response. That's exactly what I ended up doing. Not sure if it totally solved my problem yet (see my other thread, LOL). Thanks again!

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