Radio engine noise

Now-a-days, AM noise is mostly due to a loose antenna coax. It's probably fallen out of the radio plug hole or one of the inline plugs came apart.

If its am only I vote for an antenna problem. Check the cable for any rusty spots and loose connections. If there is any rusty spots on the cable it is most likely corroded inside too. If its an aftermarket radio it could just be a crappy am reciever too.

Radio Shack or any radio shop worth beans probably sells the car radio power line noise filter what you want. It's a coil/cap combo in one little black box. Hot and ground to the car, noise free hot and ground to the radio. It's essential a filter that shunts audio frequency noise in the power line to ground. After installing one, try the radio with and without the optional grounding strap that's on the back of most radios to see which way sounds best. Use a plastic insultating jury rig to hold the radio with the strap if you need something to hold the back of it and it sounds better without that extra ground. Every big city has one or two decent AM stations and FM has gone to the crapper for sure in Cincinnati.

I had a persistent AM only engine interference problem on my '86 Lincoln Mark VII for almost ten years since I purchased it used. I tried everything. Even replaced the automatic antenna with a special design optimized for AM reception. I installed multiple braided wire connections between, the hood and body, tailpipes to body etc. The fix was accidental and not entirely understood. One day when checking the radio chassis ground with the radio connected but out of the dash, I noticed that the reception was great until I replaced it in the dash. It turns out, if the radio was grounded both at the radio and also through the antenna shield at the point of the antenna body intrusion, I would experience the problem. When the radio ground was removed at the metal chassis to body connection, it worked fine. I insulated the ground at the chassis to body by removing the metal tab that engaged the body mount and it has worked great for the last 2 years before selling it last year. Stan K.

My Chrysler did the same thing. I bought a power filter, removed the radio, and damn it already had one installed. I tried it without the grounding strap for the heck of it while it was all hanging out and it sounded great.

: I had a persistent AM only engine interference problem on my '86 Lincoln : Mark VII for almost ten years since I purchased it used. I tried : everything. Even replaced the automatic antenna with a special design : optimized for AM reception. I installed multiple braided wire : connections between, the hood and body, tailpipes to body etc. The fix : was accidental and not entirely understood. One day when checking the : radio chassis ground with the radio connected but out of the dash, I : noticed that the reception was great until I replaced it in the dash. It : turns out, if the radio was grounded both at the radio and also through : the antenna shield at the point of the antenna body intrusion, I would : experience the problem. When the radio ground was removed at the metal : chassis to body connection, it worked fine. I insulated the ground at : the chassis to body by removing the metal tab that engaged the body : mount and it has worked great for the last 2 years before selling it : last year. : Stan K.

I have had that problem on my last several Fords including a '90 Taurus, my '93 F150, a '90 F150 and a couple of CV's. The problem has been resolved on each of them with a power supply filter. The one I have been using looks like a small tomatoe can about 3 inches tall and 1 1/4" across. There is a single wire on the feed end, a line to the radio and another on the radio end that attaches to ground. There is already a filter in the system as on other but, I have simple cut it from the system and replaced it with the aftermarket unit. I picked up another this afternoon at Fry's to go on my current CV. The problem has typically gotten worse as the vehicle gets older for some reason. Those who only listen to the FM side of the world may never have a problem.

I've had good experience with noise free AM reception for distant, weak stations on my '87 Taurus, '92 Grand Marquis and now my '96 Lincoln Mark VIII. All have had the premium sound systems and standard powered mast antenna. Only the '86 Mark VII had the problem and it wasn't coming from the power supply...it was antenna induced. Limiting the grounding point of the radio chassis antenna shield to only one location resolved it completely. BTW, I rarely tune the FM band. Stan K.

Several months ago, I spent a bit of time (too much) researching the possible causes. I understand the antenna is many times the cause. I was finally able to get the service manager ot the Ford dealer I usually frequent to tallk to me about the problem and the fact that it seems to be prevalant in older higher mileage vehicles. One of the primary sources he pointed out is the fuel pump which tends to get noisy with age. The fuel pump problem is somewhat less in vehicles like the CV which have a steel fuel tank that tends to shield the noise which is picked up through the antenna. Their internal solution to this source of noise is to install a filter on the pump power supply inside the fuel tank which, of course, requires dropping the tank. The filter kit is a Fomoco parts item which is still available. Their recommendation in this case for a vehicle with miles is to install a "Delco" fuel pump instead of installing a filter. According to him, the Delco pump does not require a filter to correct the noise problem.

Other common problems in their shop are antenna and radio grounds. I did quite a bit of testing on my current CV and F150. Although not terribly noisy, the CV radio did have a problem as the AM signal weakened or the car went into a garage or under a bridge. The loss of signal on the F150 was so bad, I thought the radio was bad and replaced it to learn the noise could get even worse. The radios are not yet entirely quiet but, much more useable and acceptable with the addition of the can filter. I suspect that your solution of isolating one of the ground points, inhibits reception of the RFI by interrupting it's path into the system whereas the filter is shunting it to the radio chassis ground where it is attached. I know very little about the electrinics or theory of RFI. I did try an antenna filter which introduced a loud popping into the system while greatly reducing signal strength - that did not work for me.

I kow and freely admit that my observations and experience are all anecdotal but, what the hell - it seems to be working. I am always looking for a better solution if anyone knows of one.

Lugnut

If you're experiencing weak reception on AM, perhaps replacing the standard antenna with a special one may help. I installed this loaded coil antenna on the older MarkVII in an attempt to improve the signal to noise ratio. You may want to look into it.

Thanks for the tip, The power part of my CV antenna no longer works. I will look to see if they by chance have a power antenna that my work. The factory power antenna uses a rather large hole in the fender to mount.

Just a thought, you might try asking your question on:

rec.audio.car

usually you just need a noise filter added to the power wire on the stereo or the ground wire i dont remember which i think it usually picks up the noise because the stereo is grounded to the frame