MSD Radio Frequency Interference Tech Bulletin

Tech Bulletin

Tech Bulletin

# 107

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 [phone] or
email your questions to [e-mail].

Radio Frequency Interference

Radio Frequency Interference

Radio Frequency Interf erence (RFI) can range from an annoying buzz through y our stereo speakers to affecting the re v
limiting action of your ignition. The w orst 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 breakdo wn 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 str ap from the frame to the engine is important. All
radio, CD pla yers, CB systems and other accessories must ha ve 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 awa y 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 catego­ries; 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 aff ected
slightly . If you play a tape or CD , the noise will go a way. Main­taining 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.

Supply Line noise is caused by varying loads of the
vehicle’s supply voltage. These variances are amplified
through the radio’s 12 v olt supply wire and are heard through
the speakers. Supply line noise will be audible on AM and
FM as well as during tapes or CDs. For Supply Line noise,
the MSD Noise Capacitor, PN 8830, will help .

The Noise Capacitor will act like a filter on the heavy
power supply wires of the MSD. The MSD will draw its
power though the filter keeping all of the other accessories
separate which prevents supply line noise. A side benefit
is that the Capacitor will protect the MSD Ignition from
voltage spikes or current surges.

Figure 2 - MSD Noise Filter PN 8830.

Installing the Noise Filter Capacitor

1. For best results, it is recommended to mount the Capacitor as close as possible to the MSD Ignition Control. Find
a secure mounting point and mark the location of the mounting holes. Use a 3/16” bit to drill the holes and use the
supplied screws to mount the Capacitor .

2. It is recommended to cut the MSD wires and install high quality Ring Lug terminals. The MSD power wires are 12­gauge.

3. Attach the Red wires to the positive terminal and the Black wires to the negative terminal as shown in Figure 3.

Figure 3 - Installing the MSD Noise Filter Capacitor PN 8830

AUTO TRONIC CONTR OLS CORPORA TION •

FRM23758 Revised 07/02 PRINTED IN U.S.A.

1490 Henry Brennan Dr., El Paso , T e xas 79936

•

[phone] Fax [phone]

•

Website: www.msdignition.com