2-8
REDUCING NOISE INTERFERENCE
4.2
Ignition System Interference
4.2.1
Engine Maintenance and Tune-Up
The most important step in reducing ignition noise is insuring that the engine is in proper tune. Pay
particular attention to the following points if the noise interference from the ignition system is severe:
1.
Be sure the spark plugs distributor points, and condenser are in good condition.
2.
Be sure ignition timing is properly adjusted.
3.
Be sure the distributor cap and rotor are in good condition. They should be replaced at least
every 30,000 miles.
4.
Be sure that spark plug wires make good, solid contact at each end and are routed as far as
possible from low voltage leads.
5.
Many late-model automobiles are equipped with a shield over the distributor points. Check to
see that this shield is properly positioned and securely attached.
4.2.2
Available Noise Reduction Kits
Motorola offers two noise reduction kits: Model TLN8845_ for alternator-equipped vehicles; Model
TLN6252_ for generator-equipped vehicles. These kits are for suppression of noise in the primary
and secondary of the ignition coil and for bleeding of static charges on the hood. The TLN6252_
also is used to suppress noise from the generator and voltage regulator. Figure 2-3 TLN8845_
Noise Reduction Kit for Alternator-Equipped Vehicles and Figure 2-4 TLN6252_ Noise Reduction Kit
for Generator-Equipped Vehicles show the contents of the kits and their usage.
Motorola also offers wheel static collectors (Motorola Part No. 0100534254-regular type and
0100563173-small type). Use of these items are described in section "4.7 Wheel Static" on page 12.
Most auto parts dealers can supply 0.05 µF bypass capacitors (condensers), resistive ignition wires,
and resistor spark plugs. The type of spark suppression used in noise reduction should always be in
accordance with the recommendations of the vehicle manufacturer, that is, if spark plugs are to be
replaced with built-in suppressor types, they should be in the proper heat ranges and thread sizes
for the particular engine. In each ignition system, there is a maximum amount of resistance that may
be connected between the distributor and a spark plug. If resistance-type ignition wire is used, the
length of each wire must be limited so that its resistance does not exceed the allowable maximum.
4.2.3
Ignition Coil Interference
This type of interference is characterized by a popping sound which is most noticeable when the
engine is running slowly. To suppress the noise, connect a 0.1 µF coaxial capacitor (Motorola Part
No. 0882571B02) from the battery side of the ignition coil to vehicle ground (see Figure 2-5 Ignition
Coil Noise Suppression). This keeps the distributor noise from being conducted through the battery
lead into the electrical system of the vehicle. Note that some electronic ignition systems do not route
the battery lead to the ignition coil; proper operation of the ignition system can be impaired if the
”input” terminal is bypassed.
