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Thread: Ignition current draw for EFI

  1. #1
    Champion Member Blueovalz's Avatar
    Join Date
    Jul 2014
    Little Rock, AR

    Ignition current draw for EFI

    Conflicted on where this topic goes (Electronics didn't seem appropriate either), but thought I'd throw this out to anyone searching for help on this issue I had.

    I've been using a 10 amp fuse for my EFI "ignition" wire since the beginning of my project (no where did the EFI manufacturer provide a recommended fuse rating for this wire), and it has been sufficient for any and all my street activities. During my last track event though, that changed. As I gained more experience at the track level, and as I improved the suspension settings, and as I dialed in the mapping for the fuel management, I found my lap times dropping, and my engine loading increasing on a lap by lap basis. So...the result this last track event was whenever I got into some pretty decent lap times, my engine would die on the long straight where I was at maximum HP, and maximum RPM for the longest period of time (fortunately the pit entrance was at the turn at the end of the straight!!). This happened so frequently, that at the last event, I trailered the car, and headed back home early, not sure of why I was blowing the "ignition" fuse(s), which was causing the engine to die.

    Once I got home, I replaced the fuse with an amp meter (one I used on my Tesla Coil), and set about monitoring the ignition circuit draw at various RPMs, and found that at idle (about 1K), the current draw was ~2 amps. At about 6k, the current draw increased to ~10-12 amps (simple blips of the throttle to get to red-line), with a linear progression proportional to RPM. It became pretty obvious at that point that an intermittent short was not the cause of the blown fuses, but simply a insufficiently sized fuse. I then googled various searches and found that many OEM ratings for the ignition circuit are at 15 amps, and a discussion with Holley (this is their EFI set-up) indicates that my observed current flows are consistent with design (sequential spark, so consistent current draw vs batch firing). So with all that said, I've upgraded to a 15 amp fuse for my ignition circuit (uses a 14 to 16 awg wire it appears), so I believe my issues at the track are resolved. Looking forward to next spring's events now.

    BTW, while I'm on this thought, I can't emphasize enough how nice it is to have the LED indicator fuses that have an LED light up, on the fuse itself, when they are blown. This helps tremendously in finding an electrical issue quickly.

    Last edited by Blueovalz; 01-14-2021 at 02:53 PM.

  2. #2
    Champion Member Manta22's Avatar
    Join Date
    Jul 2014
    Tucson, AZ

    A 15 amp slo-blo fuse should be a good choice for your ignition fuse.
    Regards, Neil Tucson, AZ

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