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Thread: RPM falls to zero, then up again.

  1. #1

    Default RPM falls to zero, then up again.

    I'm trying to get a 4.6L Modular Ford 4V to idle right, when I noticed that it's loosing RPM signal for split second every now & then. It's causing the engine to stall. It only seems to be happening when running under 1000 RPM. Do you think it's only a bad crank senor, or is there something wrong in the setup? Included is the datalog file. Pay attention to that right before the crank seems to loose its signal, the CL Comp starts dropping. Hmm.
    RPM Error.zip

  2. #2
    Join Date
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    Default

    Try taking a system log to see the crank & cam sensor.

  3. #3
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    Yes, record a System Log to determine if the crank or cam sensor is at fault.
    http://forums.holley.com/showthread....s-amp-Datalogs (Datalog & System Log Information)
    https://forums.holley.com/showthread...6238#post76238 (Related Forum Thread)
    http://forums.holley.com/showthread....2403#post72403 (Ford Modular/Coyote - Crank/Cam & Ignition Setup Information)
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  4. #4

    Default

    Thanks, I'm new to the Holley EFI, and didn't know about the ability to system log.
    Did a system log and regarding to Crank & Cam, nothing seems odd there. So this still remains a mystery to me.
    Thanks for the links Danny, I will dive into them. But here is the system log file, if anyone wants to have a look.

    Could it be a setup error? Running two Holley coil drivers, wasted spark coils.
    Ignition type set at: Ford Mod 2V/4V waste spark coils.
    Firing Order: 13726548
    Maybe I should setup a Custom Ignition Type?
    Attached Files Attached Files
    Last edited by einarak; 03-07-2018 at 02:12 AM.

  5. #5
    Join Date
    Nov 2014
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    Always post your Global File with your datalogs. It helps to see your settings.
    Did the engine act up during your system log? If not, then you need to make a another system log and catch it acting up.

  6. #6

    Default

    I've updated my earlier post with the Global File. Yes, it was acting up in the system log, it can be seen on the RPM that it's just like it's shot and then comes back to life, always at around 1000 RPM. And when I got it to stay steady, it happened every 5 seconds (from 20s to 50s in the log). Attached are same files again, Global File & system log.
    Attached Files Attached Files

  7. #7
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    I'm not familiar with the way Ford sets up its cam & crank sensors, but I will tell you what I see in the log. You are using a 36-1 missing tooth crank sensor and a single pulse crank sensor. When the engine shuts down, it's doing it at the same spot in the engine's four stroke cycle. On the Digital Rising signal of the first tooth past the missing tooth it will lose RPM signal. This spot is also five teeth before the Digital Rising signal from the cam sensor. The RPM ERROR will cause the injectors to turn off. It will lose RPM signal for 360° plus one or two teeth. Then the RPM signal comes back and the injectors will turn back on and the engine starts to run again. It also does not lose cam & crank signal when it loses RPM signal. You could try a custom crank & cam settings, I would call Holley Tech on that.
    Last edited by 81 TransAm; 03-07-2018 at 11:26 AM.

  8. #8

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    SOLVED Thank you for your help 81 TA, it got me a whole lot closer to the problem. I just took it for granted that I could use the pre setup Ignition Type profile for Modular Ford, but that one was the root of the problem. After configuring a custom setup for magnetic 36-1 crank sensor and magnetic cam sensor and fiddling with the Minimum Signal Voltage & Filtering, the problem went away. Smooth idling at 750 RPM like never before! Now I just need to dig up my timing light to dial in the Inductive Delay & Timing Offset.

  9. #9
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    Default

    Good to hear you found the problem.

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