Technical Service Bulletin Radio Interfering due to External Factors

Subject: Radio Interference    Models: 911 Carrera ALL

Bulletin Number: 85 – 07

Radio Interference complaints may be caused by either external factors vehicle components, or radio system failure.

Therefore, a clear differentiation must be made between these areas of possible problems.

Below is a troubleshooting guide for radio reception interference:

  1. Interference due to external factors.

Radio reception could be influenced by the following factors:

  • Landscape (mountains, trees, poles, buildings)
  • Reflection of radio waves (multiple reception)
  • Weak broadcasting stations
  • Stations with changing broadcasting power
  • Transmitter frequency not adjusted precisely in radio.
  • Transmitter or frequency overlap (large signal)
  • Weather clouds (high pressure area)
  • Interference could be considerably stronger for stereo reception than for mono reception.
  • Strongly changing reception signals.
  • Interferences from Engine Components

-Tack, sizzle. Speed dependent, noise. Remains even after releasing accelerator pedal. Is caused by unshielded spark plugs, corrosion (green coat) on spark plug connectors, or the alternator is defective. Can be solved by shielded spark plugs, which are standard in all types of since M.Y 1985.

-Noise occurring occasionally (temp. dependent). Caused by a defective alternator. Test; take off alternator drive belt. (Important-911: cooling air blower). Replace Alternator, if noise has stopped.

-Slight interference in weak stations. Caused by ignition system (spark gaps). Fix by replacing distributor cap, distributor rotor, ignition leads, connectors or spark plugs.

  • Interference from other components

-Whistling noise, caused by low frequency interference from alternator. To correct, check whether radio or additional amplifier impedance coil is installed. Check ground connection too between radio and additional amplifier.

-Hissing, sizzling. Interference noise amplified especially in treble range. Caused by treble transmission (hi-fi radio, equalizer, treble regulator). Tune in different frequency range or reduce high frequency to resolve.

-Crackling in speakers, reception interference. Caused by loose contact. Check oxidation and tightness of all connections and plugs between antenna-radio speakers additional amplifier.

-Weak radio reception on all stations. Caused by antenna or leads loose. Windshield antenna problems include antenna amplifier defective, loose plug connection (amplifier), antenna wire broken (visible area), amplifier not receiving power from radio (+ positive connection). To fix, check tightness, replace if necessary. Replace amplifier, check tightness. Replace windshield. Check connections and power check wire tightness. Depends on your specific problem when it comes to what to replace or check.

-Howling, hissing when windshield wipes are used. Caused by no ground connection between wipers and body. Make sure ground connection according to sketch or pictures (wiper motor must be removed). After installation; check power flow in ground connection.

radio sketch

Body end installation: M 6 x 20 hex. Hd. Screw, nut and washer. Hold screw in position with tape to make installation easier.

radio sketch for fix

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