Hearing lots of static through your car radio can be incredibly frustrating, especially if you are trying to listen to your favourite talk radio program or music station. While static occurs because you are simply not within range of the station transmitting the signal, some static is actually caused by your car. More specifically, radio frequency interference (RFI) emitted from the car's ignition system causes static, especially in AM signals. If you have experience working with cars, this kind of static can be remedied by following a few simple steps.
Think back and try to remember when you first started hearing static in your car's radio. Consider any changes made to the car, replacement parts, damages, etc., that could have affected the radio. See if the radio receives static only when certain mechanisms are running, like the air conditioning or windshield wipers.
Listen for static noise in the accessory, on and run positions of the ignition system. Each turns on a different part of the car's electrical system. Isolating the noise in one of these ignition positions will likely pinpoint the static.
Find a cheap AM radio that does not contain much RFI-reducing circuitry. Turn on the radio and wave it back and forth near the car's engine to locate the specific source of magnetic interference. On older vehicles, the likely source of RFI is the coil, spark plugs, spark plug wires and distributor.
Check the spark plug wires with an ohmmeter. Keep in mind that the aramid-core type carries a resistance 2,000 to 5,000 ohms per foot, making them bad transmitters of electrical noise. RFI chokers like this need regular maintenance, and they'll produce a lot of noise if you don't replace them often. Replace them with resistor plugs to reduce RFI.
Install fresh spark plug wires. Pay close attention to the wires' routing because often the manufacturer arranges wires out of sequence (for example, 2-6-8-4 on one side in a V8 engine).
Look for an RFI-reducing capacitor wired from the positive side of the power to the ground. This can be replaced to reduce RFI noise if the manufacturer used an external mount. These are usually located on the inner bumper walls, though they can also be found hanging from the primary side of the car's ignition coil. Make sure there is a good connection on each side of the capacitor.
Check to see if the fuel pump is causing the static noise. The pump basically runs for a few seconds when you turn on the car to build fuel-system pressure and then shuts off. You can put in another pump, but usually the capacitor method in step 6 is more cost-efficient.
Another source of RFI might be coming from the plastic or metal plates that highlight the wide cam covers on the engine. These can create audio interference if the covers are not properly installed.