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Thread: Constant 12 volt signal only when engine is running?

  1. #1

    Default Constant 12 volt signal only when engine is running?

    Is there a constant 12 volt signal that one of the pins have that can be used to turn on an alternator (external voltage regulator)? Kind of like an ignition, but only once the engine starts running, but also shuts off if the engine stalls, but the ignition is still on? I know one of the ways to accomplish this is with an oil pressure switch, but I've heard too many of those failing and I figure a much more reliable method would be doing something from the ECU? There is minimal to no draw on this as this is just the "turn on" wire for my voltage regulator and I have a separate power wire that actually runs the regulator.

  2. #2
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    Check the EFI fuel pump relay.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  3. #3

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    Sounds like a great idea! Just to confirm because I actually run my fuel pump independently controlled anyway, and the fuel pump relay is entirely available for my use. I do use the fuel prime percentage for startup, which in multi-port fuel injection "injects" the calculated pulse as soon as it detects any cranking? If I turn the fuel PUMP prime off, but leave the fuel prime still on, will it still throw the extra shot of fuel when it detects the first cranking pulse? Lastly in this configuration, I assume the fuel pump relay is programmed to turn as soon as Crank-To-Run RPM is reached and not during cranking correct? Just trying to confirm how I believe the system is programmed. Thank you in advance for the suggestion!

  4. #4

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    Don't forget the base setup in the ECU has a "prime" timer. Also isn't there a dedicated external Rev Limiter I/O pin? (Not sure if that's useful.)

  5. #5

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    Just setup a +12V output that's active when RPM is greater than or equal to 400 RPM.

  6. #6

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    @quarterbooty: Thank you. That makes sense. What if I wanted to setup a +12V output that activates something over 185°F (like oil temperature for example), but deactivates below 170°F. Kind of like how a fan thermostat works for example. Is there a way to do this?

  7. #7
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    Yes, setup a "12 Volt" type Output (in Inputs/Outputs ICF). Enable it, Configure it with "Enable Secondary Deactivation" (Hysteresis Mode) and Pin Map it. Then connect that Pin Mapped wire to whatever you're powering. A relay must be used if the component draws more than the ECU's Output rating of 2 amps maximum.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  8. #8

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    Thank you Danny! Really appreciate it!

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    29,091

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    You're welcome.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  10. #10

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    If I set it up the way Danny mentioned, I assume that provided ignition is on it won't matter if engine is running to activate? Meaning it'll only be temperature dependant? If I was thinking of also adding a 12 volt input that also needs to be activated and activating that input with the fuel pump (green wire). Anything wrong with my thinking and or a better idea of how to go about this?

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