Symptom Descriptions

INTERFERING NOISES
The vehicle ignition system is a possible source of radio interference. This high-voltage switching system produces a radio frequency electromagnetic field that radiates at AM, FM, and OB frequencies. Components have been designed into the vehicle to minimize this concern. Vehicle electrical accessories and owner add-on accessories may also contribute to radio interference. Furthermore, there are many noise sources which are external to the vehicle. These include power lines, communication systems, ignition systems of other vehicles, neon signs, etc.

Noise or static may result from many causes. Some of the most common sources of radio noise are listed below:

Ignition Noise
The most effective method of evaluating ignition noise is to compare the radio chassis performance with the engine running versus with the engine not running. If ignition noise is present only with the engine running:
- Check to see that the spark plug wires are the suppressor type and that the spark plugs are the correct resistor type.
- If so equipped, check to see that the carbon center insert in the distributor cap is secure.
- If so equipped, check the distributor cap and the distributor rotor electrodes for silicone grease as this may cause ignition noise on FM. This noise is characterized by a "motor boat" type sound on weak to moderate strength stations. The noise can only be eliminated by replacing the distributor cap and the distributor rotor without grease.

Missing or Poor Grounds
Check bond strap grounding effectiveness by wedging a large file between metal parts to ensure proper ground, such as between the tail pipe and body, or between the fender and frame, while the radio chassis is playing and the engine is running. Listen for a decrease in the objectionable radio noise. If a reduction in radio noise is noted, first try tightening body and exhaust system clamps and brackets. Then, if necessary, install a new bond strap between the two metal parts to ensure proper ground.

Missing or Damaged Noise Suppression Components
Noise suppression components may be malfunctioning or missing.