If it happened suddenly, you should look for what changed. Examine the ignition wires, boots and coil in the dark for arcs. Make sure all ignition connections are clean and secure.
Take it from an old electronics engineer, it's much easier to eliminate RFI at the source than to filter it out at the receiver.
Modern vehicles (less than 30 or 40 years old, depending on the make) are designed to suppress noise; some of the older ones are not and "add-on" noise suppressors (misc. capacitors, etc.) were commonly installed along with radios. Generally speaking, if a car came from the factory with a radio, then appropriate noise suppression is built in.
If you suddenly have noise, it is because something broke.
Gasoline engines can radiate two distinct kinds of noise, one kind from the ignition system and the other from the generator/alternator. (Alternators are generally pretty quiet, but the older generators can buzz pretty good...) Depending on how your car is wired, you may be able to tell which you have by reving the engine up and switching the switch to the "accessory" position. If the noise continues while the engine continues to spin, it is generator noise. If the noise stops, it may be ignition noise or you may have just turned the alternator off, too (this test works well with generators, not always with alterenators).
You need to find what went wrong and fix it.
Jerry
Sudden change without you doing anything means something broke. Likely suspects include the ground from the radio, the antenna ground or the cable itself has a problem.
I am trying to add an ignition surge/static suppressor to my old Triumph. This year I suddendly have static on FM and massive static on AM. From my youth I remember vaguly about hanging a capacitor off of the coil to funtion as a suppresor. Which side of the coil does the condensor attach to?
Capacitor (also called the condenser) is necessary for a 'point and condenser' ignition system to create spark plug voltages. It has nothing to do with noise suppression. Meanwhile, spark plug wires should be resistance wires because the relationship between that resistance and how wires become inferior antennas.
Meanwhile the ignition system does not create FM frequency noise. So where is the noise coming from? Your post implies you want to solve the problem rather then do the work - first learn what the noise source is. From your post, we have no reason to blame the ignition system. Others have listed more likely reasons for noise - bases upon what you have posted.
Among the many 100 different reasons for noise is that your radio system no longer makes a single point connection to chassis ground. Or the antenna shield lead (maybe a connector or the connection to antenna) is loose. Or that antenna wire shield is suddenly touching conductive chassis. Or DC power supply filter has failed. Or .... long before asking what to fix, instead ask what could be the noise source. Only long after that is decided are you ready to ask for solutions. Welcome to an art form - EMI/RFI. Trying to fix things with ferrite beads without first knowing what to fix should eventually teach you why 'try this and try that' will only teach you why that is called shotgunning.
To answer the question, RFI suppression caps go on the coil POSITIVE on negative ground vehicles. The point arc suppression cap coes on the negative side (across the points).
Or the factory installed RFI cap fell off, or went bad.
Not totally true. There CAN be 2 caps, one on each side of the coil. As for plug wires, do yourself a favour and buy "magnetic suppression" wires, not solid core or carbon core wires.
AM and FM will both get "static" from a power feed disturbance. Whether Alternator/generator or ignition. Take off the fanbelt - if it's quiet it's the generator/alternator, or the regulator. If not, does the "static" change directly with engine speed? If so it is quite possibly an ignition primary problem - which a suppression cap can solve. If it is not engine speed dependent it COULD be the instrument regulator. Pull the instrument fuse - if it goes away, replace the old thermal regulator with the appropriate solid state reg pack.
Did you check things like body grounds and bonding of bohy to engine? Cable could have been left off when the head gaskets were replaced - has been known to happen and cause static.
Thanks all for the replies. I will put forth effort at solving the static cause based on all of your suggestions, if that does not produce results then I look to solve the symptom.
THere is a bit more to the story than I originally posted. THe static appeared as I began to use the car this year - was not there last fall. On Halloween morning the head gasket burned thru and subsequently the car was parked for the winter. As part of pulling the head, the ignition wires and the plugs were removed. Both the wires and the plugs (resistor) are newer (have to check the vehicle log but I am guessing about 2 or 3 years (9,000 to 12,000 miles). Nothing was done in the interior of the vehicle, although it is conceivable that a ground might have worked itself loose.
The noise is very RPM sensitive. At idle it is a minor static on FM, at
3K rpm the static begins to overpower the programming on FM (AM is pretty much useless since the static began).
The term "RPM sensitive" is generally construed to mean that the pitch of the noise varies with RPM, not the volume. If the pitch varies with the engine speed, then the problem is either generator or ignition. If the noise is simply random "hash," something like a hard rain on a tin roof that becomes more intense as the RPM (and consequently, the vibration) increases, the probable cause is a bad ground somewhere.
Jerry
I wonder if I guy couldn't take an air chisel with a flat tool on the end just rat-a-tat around (lightly) various connection points to see if the problem changes intensity.
Pete Stanaitis
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aribert wrote:
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