MSD Radio Frequency Interference Tech Bulletin - Manual

Radio Frequency Interference
MSD’s Tech Bulletins are designed to give you a more in-depth
understanding of the ignition system and its components. If you have any other questions about the
subject or MSD products you can contact our Customer Support Department at (915) 855-7123 or
email your questions to [email protected].
Tech Bulletin Tech Bulletin
# 107
Radio Frequency Interference
Radio Frequency Interference (RFI) can range from an annoying buzz through your stereo speakers to affecting the rev
limiting action of your ignition. The worst part of all of this is the fact that you can’t see the problem! This makes it even
more frustrating but there are steps you can take to isolate the problem.
First you need to isolate the RFI. If the noise appeared after installing an MSD Ignition, bypass the ignition. If the
interference disappears when the MSD is bypassed, then it has added a factor that directly, or indirectly causes the
interference.
Due to the increased output of the MSD, the breakdown of adequate components like the spark plug wires, cap and rotor,
spark plugs or related components may be brought into the light. These ignition components should be inspected and
replaced if wear is present. Also check the following:
The chassis and engine must have a common ground. A ground strap from the frame to the engine is important. All
radio, CD players, CB systems and other accessories must have a common ground connection to the chassis as well.
The Heavy Black wire of the MSD must be grounded to the battery negative terminal, the chassis or the engine.
Try to mount the MSD Ignition away from the vehicle’s antenna.
The spark plug wires must be spiral or helically wound wires and in good condition. Solid core wires cannot be used
due to their inability to suppress electrical noise. Helically wound wires are designed to suppress electrical noise and
should always be used.
Identifying and Preventing Radio Noise
Radio noise can be broken down into two distinct catego-
ries; Radio Frequency and Supply Line.
Radio Frequency noise is generated by the secondary side
of the ignition (coil wires, cap, rotor, spark plug wires). This
noise is radiated into the air and picked up by the antenna.
This noise will be noticeable on the AM band and will be
louder between stations. The FM band may also be affected
slightly. If you play a tape or CD, the noise will go away. Main-
taining the secondary side of the ignition system is important
in eliminating radio frequency noise.
MSD offers a dielectric grease called Spark Guard. It is
available as PN 8804. This grease reduces the chances of
voltage leaks which can cause radio noise. Plus, it helps with
plug boot installation and removal while preventing any chance
of moisture build up inside the boot.
Figure 1 - MSD Spark Guard.