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Thread: MSD 6AL 6420 Disable RPM?

  1. #1

    Default MSD 6AL 6420 Disable RPM?

    Page 10 of the Sniper manual under Sensor Verification, it says in bold, "If ignition box or distributor has the ability to send RPM signals with initial key on (such as Tach Sweep or REV Limiter Verification), these setting must be disabled. Reference ignition system instruction".

    I've looked over the MSD manual online PDF and find nothing of these features or whether it sends these signals with key on. The 6AL has the Rev Limiter 'Pills'. I'm hoping one of you knows for certain what or if I need to do anything with the MSD before initial startup. Thanks.

  2. #2
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    If you're using an MSD Digital 6AL CD ignition box with EFI, ensure the Rev Limiter Verification feature is disabled (LINK). See post #4 of this thread below.
    MSD Ready-To-Run Distributors (even without the MSD Digital CDI box): http://documents.msdperformance.com/...r_addendum.pdf (MSD Ready-To-Run Rev Limiter Addendum)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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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    Thanks Danny! If I'm reading this correctly, I should be able to cycle the key and if my Tach does not move to the set Rev Limiter setting, then this feature has never been enabled and I can do nothing? I know I did not enable this feature when I installed the MSD system (actually the Sniper manual is the first I've even heard of it), but would like to verify anyway.
    Last edited by BQUICK; 06-22-2018 at 11:19 AM.

  4. #4
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    If you're using an MSD Digital 6AL CD ignition box with EFI, ensure the Rev Limiter Verification feature is disabled:
    http://documents.msdperformance.com/6425.pdf (MSD Digital 6AL Instructions - Read Center of Page 5!)

    REV LIMITER VERIFICATION
    The MSD Digital 6AL has an optional built-in Rev Limiter Verification feature. When the key is in the On position (not cranking or running), an RPM signal is sent to the tachometer to verify the unit's rev limit setting. With this function users can be sure of their rev limit settings before each drive. This feature is not activated from the factory. To enable this feature, follow the procedure below.

    Note:
    It is important to note that this feature should NOT be used with EFI systems. When activated, an RPM signal is sent to the tachometer.
    With an aftermarket EFI system, this will activate the injectors causing a flooding situation.


    Enable Rev Limit Verification
    1. With the ignition switch in the off position, ground the Gray tach output wire.
    2. With the Gray wire connected to ground, turn on power to the ignition without starting the engine.
    3. Hold the Gray tach output wire to ground for seven seconds. (AT LEAST five seconds.)
    4. Release the wire from ground before ten seconds have passed.
    5. To confirm the process has worked, cycle turn the key On. The tachometer should sweep to the RPM limit set on the ignition.

    As soon as this process is complete the feature will be activated. The Digital 6AL uses the red LED to help indicate when an adequate amount of time has passed to release the Gray tach wire. The LED will turn on after the wire has been grounded for five seconds and will turn off at the 10 second mark. To deactivate the feature again, repeat the same process.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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.

  5. #5

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    My comments/questions in the previous post were asked (post edited) after I'd read the stuff you posted for me. I'll just check it out to be sure. Thanks again.

  6. #6

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    The MSD 6420 doesn't have the sweep/verification function. I'm using one without issue.

  7. #7

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    And then I find the thread you responded to, from a guy with a 6AL that wouldn't work. Good info in case I run into something similar, I'll have somewhere to look. My MSD is probably 15 years old with the 'pill' rev limiter. Will find out Monday. Thanks.

  8. #8

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    Yes, mine has been installed since 2004 and has been dead-on reliable.

  9. #9

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    Hello Danny. I like the Rev Limiter Verification feature of my tach with the MSD 6AL and Holley Dominator direct port EFI. I have it set around 6500 RPM most of the time. I have hot staring issues as well sometimes. So I looked at my injector pulse width at idle which is around 2.3. Then I looked at the injector pulse width when turning the key on before start and it shows around 7.8. So now I open the throttle about 30% and it starts much faster with the added airflow. What options do I have to keep the Rev Limiter Verification feature? Just thought maybe installing a toggle switch in the wiring somewhere to turn it off & on, or maybe something in the software that can be adjusted? Thanks Danny.

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