Static on AM Radio

The best cure I have found after making sure all the grounds were good is the old fashioned cannister type power line filter you can get at most auto or electronic stores. It should be installed as close the the radio as possible.

Lugnut

A couple of add-ons: The electric fuel pump is often a source of interference for AM. On some models there is a TSB fix for this. I have very successfully corrected interference problems on Ford radios by replacing both the antenna and coax, using a better shielded coax. The factor Ford AM radio in many of the 90's cars and trucks I've fooled with is itself not helpful. The broader the tuning, the more fidelity you have, but the more open the input stage is to interference. It seems that most aftermarket radios do a better job of filtering interference than the factory radios I've fooled with.

CJB

electric fuel pump running?

Eisboch

Doesn't the pump only run 'on demand' to keep the fuel system pressurized? It would only run for a second or two if the engine was not running.

One thing that could be running is the fan. Is the static frequency related to the speed of the heater/ac fan? As CJB suggested, various ferrite filters could fix the problem but you should make sure you have proper grounding. There should be a ground lug on the back of the stereo and that needs a good strap to chassis. you might test this by taking a piece of wire and making a temporary ground strap between the unit and chassis to see if it makes a difference.

I am assuming that the radio used to work properly and you have also checked the antenna connections.

Stephen N.

I should have mentioned that my radio is an aftermarket unit ...

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Not a canister filter, you need a in line iron core choke to remove the "line noise" from vechicles electronis. If you are so inclinded you can unstall some .01ufd bt pass capacacity in power wires feed ECM and other electronics as this can help sometimes too. (you want the at the actual power feed into unit)

----------------- The SnoMan

There lays part of your problem. Some after market radios do not filter the input power very good if at all. Install a inline filter chake as mentioned above in postive power leg feed.

----------------- The SnoMan

Yes, I suggest it could be the electric fuel pump causing the interference. Do this, pull the antenna lead of that radio and that will tell you if the noise source is coming down the antenna leadin or from the power line. I will bet on the power line which can be filtered with a good choke capacitor type of filter. Try radio shach for that. If you find that it is coming dwon the antenna then the problem might be a bit tougher and you mnay need to find the source and bypass at the source such as the brushes is a motor or what ever is causing the radiation of radio frequency energy. Remember, without me getting too techinical, FM modulation varies the frequency at a audio rate whilst AM modulation is varied at an amplitude rate. With FM the nise id "clipped by a limiter". In am not so and since most noise if AM, it is best killed at the source. Hope this helps.

Bill

The HVAC blend door control circuit was causing interference on our

1997 Ford Expedition. As you changed the temperature knob you could hear the radio static change. Fortunately it was under warranty.

-CT