Poor AM Reception All

K. Poor AM Reception - fading, engine noise or interference

1. Ignition System AM Interference

2. Charging System AM Interference

3. Fuel Pump Motor AM Interference

4. Brake "Pop"

5. Horn "Pop"

DIAGNOSTICS:
Perform the following to verify the noise concern.

1. Ignition System AM Interference:

^ Engine running.

^ Tune in a weak AM radio station.

^ Vary the engine RPM.

^ Listen for ignition noise. The frequency varies with engine RPM.

2. Charging System (Alternator) AM Interference:

^ Engine running.

^ Tune in a weak AM radio station.

^ Vary the engine RPM.

^ Listen for alternator whine. The frequency varies with engine RPM.

3. Fuel Pump Motor AM Interference:
^ Engine not running.

^ Tune in a weak AM radio station.

^ Listen for AM static or noise that occurs only when pump is running.

4. Brake "Pop":

^ Engine not running.

^ Tune in a weak AM radio station.

^ Depress the brake pedal.

^ The "pop" occurs when the brake light is activated.

5. Horn "Pop":

^ "Popping" noises heard through speakers when horn is used.

SERVICE ACTION:

Perform ALL of the following to service the above noise issues.


1. Inspect the antenna cable connections for signs of damage or corrosion.

NOTE:
REFERENCE TSB 91-2-7 FOR WATER LEAK CONCERN ON 1989-1990 MARK VII.

2. If the antenna connector is corroded, replace the antenna.

3. Check for possible water leaks or holes where water can enter from road splash. If found, seal holes where water entry is found.

4. Fill the antenna female connector with grease (F2AZ-19584-A).

5. Install the one piece, double shielded antenna cable (F1VY-18812-A) down the right hand side of the vehicle from the radio to the antenna, beneath the carpeting.

NOTE:
DO NOT BUNDLE EXCESS CABLE LENGTH IN TIGHT BUNDLES AS THIS MAY DAMAGE THE CABLE, AND ADVERSELY AFFECT RECEPTION PERFORMANCE. SECURE CABLE WITH TAPE AS NEEDED TO PREVENT POSSIBLE RATTLES.

6. Apply grease (F2AZ-19584-A) to the outside of the installed antenna cable connector. This will prevent water entry into the antenna connector shell.








7. Install underbody ground strap kit (D5FZ-19A095-A) (contains three ground straps). Refer to Figures 9 through 11 for proper locations to install the ground straps. It is very important to install the ground straps as specified.

8. Replace the production horn relay with a noise suppression horn relay (E6DZ-9345-A). Refer to TSB 90-24-9.

PART NUMBER PART NAME CLASS

F1VY-18812-A Cable Radio Antenna B
F2AZ-19584-A Electrical Grease C
FOVY-18887-A Radio Interference Kit B
F1PZ-18B925-A Filter, Radio Receiver C
D5FZ-19AO96-A Ground Strap Kit B
E6DZ-9345-A Horn Relay B
D6AZ-19627-A Tape BG
F2PZ-19A095-A Ground Strap C