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Thread: Holley HP EFI RPM PWM

  1. #1

    Default Holley HP EFI RPM PWM

    Currently running an LS7 in a '93 RX7 with a Holley HP EFI.

    I connected the tachometer wire to my gauge, and it's currently reading double what the RPM actually is. I was informed that I could use a PWM Output for the RPM signal, but I'm a little bit lost on how to configure that.

    My tachometer is setup for 2 pulse per RPM, and I believe the Spout wire is setup as 4 pulses per RPM. Thanks in advance.

  2. #2
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    Quote Originally Posted by GTR View Post
    Currently running an LS7 in a '93 RX7 with a Holley HP EFI.
    http://forums.holley.com/showthread....7583#post47583 (Tachometer Signal Wire - Read "Holley LSx Main Harness")
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  3. #3
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    Your tachometer needs to be changed.
    There's usually a wire you can connect or clip, to make it read correctly.
    A PWM Output will not work because it's a 12V tach signal. It will fry your tachometer.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  4. #4

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    From my understanding, the blue/white wire that is used to run HEI ignition is changed to 12V square wave when it's running DIS.
    This is the wire I ran to my tachometer. It is obviously too high for my setup.
    So it is impossible to use one of the PWM Outputs to use as a tach signal?

    Holley LSx Main Harness:
    The end of this document has a note about the LSx loose blue/white wire for a tachometer:
    http://documents.holley.com/199r10597rev2.pdf (LSx Main Harness Notice)
    It outputs a 12V square wave, same as the Tach Out on an MSD box. No adapter required.
    Some factory OEM tachometers may need a "tach signal amplifier" to function properly.

    Holley EFI Wiring Manual:
    EST Output – Activates the EST Output trigger (+5V square wave trigger) that is used to drive an HEI ignition module (Pin A28).
    When a DIS/CNP system is configured, this outputs a +12V square wave that can be used to trigger a typical tachometer.

  5. #5
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    Quote Originally Posted by GTR View Post
    I was informed that I could use a PWM Output for the RPM signal, but I'm a little bit lost on how to configure that.
    Who told you this? Which tachometer do you have? I haven't heard of a tachometer not working with Holley EFI.
    http://www.yellowbullet.com/forum/sh...3#post35382793 (Related Forum Post)

    So it is impossible to use one of the PWM Outputs to use as a tach signal?
    I've never done it, but there's some instruction on it, in the Holley EFI Tier 2 Training Manual (page 17 - "Inputs & Outputs" section). Ensure your tachometer can receive a PWM ± signal, and if so, you know it's frequency (or tachometer damage will result). Contact Holley Tech Service (LINK) for the aforementioned PDF document. It's too large to attach here on the forum.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  6. #6
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    Excuse me for hijacking, but will the tach signal from the blue/white wire drive a Auto Meter tachometer?
    '81 Mustang Cobra/LSX powerplant
    Poorly built ERL LS454 rebuilt by Extreme Racing Engines
    1.27 60', 9.14@150.47

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    Quote Originally Posted by SSSTANG View Post
    Excuse me for hijacking, but will the tach signal from the blue/white wire drive a Auto Meter tachometer?
    Yes.
    http://forums.holley.com/showthread....7583#post47583 (Tachometer Signal Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  8. #8

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    From experience, some of the Auto Meter tachometers are Auto Gage.
    Auto Gage needs the signal conditioner that Auto Meter sells, to hook up the tach to MSD boxes.

  9. #9
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    Quote Originally Posted by BITE_ME View Post
    From experience, some of the Auto Meter tachometers are Auto Gage.
    Auto Gage needs the signal conditioner that Auto Meter sells, to hook up the tach to MSD boxes.
    The A28 blue/white wire operates my Auto Gage (by Auto Meter) tachometer perfectly, without a signal conditioner.
    Before I converted to DIS, I ran a CD ignition box (although not MSD), and I never needed a tach signal conditioner.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  10. #10

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    It's mainly the older ones that I always had to use a conditioning box on.
    I did about 20 installs on imports, and 10 installs on American cars.
    About half the installs needed the box. All the tachs were labeled Auto Meter.
    This was from 1985 to 1997. All used MSD boxes.

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