MSD 83647 HEAT HEI Module Installation - Manual (Page 3)

INSTALLATION INSTRUCTIONS 3
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PROGRAMMING THE REV LIMIT
A tachometer is required to set the rev limit. The limit is
programmed by running the engine at half the desired
rpm, then momentarily grounding the Gray tach output
wire from the MSD. A Gray jumper wire is supplied to
connect to the tach with another tee-splice coming off to
use for programming. A switch may also be installed to
ease adjustments of the limiter (Figure 4). The default rpm
limit is 10,000 rpm.
1. Start the engine and bring the rpm to half the desired
rev limit (for a 6,000 rpm limit, raise the rpm to 3,000).
2. While holding the rpm steady, short the Gray tach wire
to ground for approximately one second. Note that the
tach will go to zero while grounded.
3. The tach will now display the programmed rev limit
amount for two seconds. If this value does not register
on the tach, repeat the procedure and try a different
ground source.
Note: This rpm confirmation only displays when the HEI Gray wire is being used to trigger the
tachometer.
REV LIMITER VERIFICATION
The MSD HEAT HEI Module 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
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 could 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 the ignition on 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.
To deactivate the verification feature, repeat the process.
Playback Tach: If you use a playback tach, be sure to check the high rpm value prior to turning the
key to the On position. When the key is in the On position, the rev limit will be displayed and may
override the tach memory.
Figure 4
TO
TACH
OPTIONAL
PROGRAMMING
SWITCH
GRAY