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Bouncy timing. High Inductive Delay.

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  • Bouncy timing. High Inductive Delay.

    Hello all. I'm hoping someone with a good technical knowledge can help point me in the correct direction. I’m running an unusual and not officially supported ignition setup. I have a GM small cap HEI distributor (Delphi replacement less than 2 years old), with a magnetic pickup. The pickup feeds the RPM signal to the Sniper.

    The stock (Delphi replacement) HEI coil is being driven by the coil driver which comes with the Sniper. Dwell is at 2.5. Reference Angle is set at 0, which phase the rotor same as the factory computer.

    The issue is that when the static timing is enabled at 10, and the engine is revved, the timing (as seen with the timing light) is not very stable. It sort of bounces around, by as much as about 15 sometimes. Once the RPM is held steady it settles in one place and doesn’t move very much. To make that settled place be 10, an Inductive Delay of about 685 is required.

    I feel this Inductive Delay is especially high. I also feel the timing should not bounce like this as the RPM increases. The problem this is causing, is that when accelerating, the engine sort of surges, like the timing is retarding and advancing and I believe it is. What I’m unsure of is what could be causing this, and what exactly the Inductive Delay acts upon.

    Do I have a bad coil or coil driver? Could my magnetic pickup have a bouncy signal? it would have to bounce 10+ to match up with what I see with the timing light. Minimum Signal Voltage is set to 0.9 volts, and it idles fine and runs strong when at stable RPM.

    The harmonic balancer (and thus the timing marks) was new less than two years ago when this engine went in. I've had the Sniper on the car for most of that time, and I think I've been chasing this problem ever since. if I switch back to coil -, and let the module control the timing, I don't have any surging. The module has two steps to the timing, and it's not a real timing map.

    I'm hesitant to drop $800 on the whole Sniper ignition package. I would probably go to a mechanical distributor before doing that. But I'd like to figure out where my problem is originating. If anyone with a greater understanding could point me in the right direction I'd really appreciate it.

  • #2
    The Sniper coil driver module will eventually burn out if your coil resistance is low (like an HEI open winding coil). Possibly your Inductive Delay and erratic timing is due to the coil driver struggling with excessive primary current.

    The Sniper coil spec limits are about:
    >0.7 ohm - Primary resistance
    <140 mA - Primary current​

    You can change your coil to an oil-filled type that matches the Sniper limits or add a multi spark/CD ignition box in place of the Holley coil driver module. You shouldn't need to buy the full-boat HyperSpark ignition. A friend installed an MSD "6EFI" box because his "Blaster" coil burned-out the coil driver.
    Last edited by Candu SNO; 09-23-2022, 06:24 AM.

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    • #3
      Thanks for the reply. That makes a lot of sense. I haven't measured yet, but my coil is probably between 0.3 and 0.5 Ohm. So much too low. Amperage could be anything, but no doubt is too high at that low resistance. I wonder if I could test this theory by putting a resistor inline with the primary side of the coil.

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      • #4
        Coil primary resistance is notoriously difficult to measure accurately, you probably have to rely on published specifications.

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