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Discussion Starter · #1 ·
Ok... so I'm wondering if I may have some sort of electrical problem. I posted a while back about my horn randomly stopping. I could hear the click of the relay, but no horn, and only seconds after I last heard it work. I wrote it off as a bad horn, and was going to replace it. Then I started picking up some interference through FM. I was broadcasing my CD player to a low FM station, and I was getting interference that was sequenced to the revving of my engine. I assumed this was either the batteries going on the FM transmitter (combined with a 91 car having some older wiring that was wearing), or maybe because it had been raining hard and some moisture got somewhere it shouldnt. Then it went away, and a few days later the FM interference came back, but this time it carried over into all FM stations and it was not wet outside. I switched over to AM expecting the noise to be much much worse, but there was none... crisp audio with no interference on AM. The next day the interference was gone. Tonight I hit my horn as an instinctive move during a close call, and to my suprise it worked! I changed my plugs and wires recently, but that's the most electrical work I've done to this car. Any ideas WTF is going on here?
 

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Did the radio noise start after you replaced you wires? It sounds like to me you are getting ignition interferience noise. I dont know what kind of wires you got but some of the lower quality wires dont have as good of insulation to help prevent this. Some cars have a capacitor located right by the coil to help with preventing interferience.
 

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Discussion Starter · #5 ·
hmmm, they are double silicone or something like that. $40 for them. I did notice that the old wires had the wire going from the coil to the cap routed strangely and it was connected to a hose with a strap... thought it was odd and didn't do the same when I put new wires in. The thing is, that it doesn't happen all the time.
 

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Radio interference that increases in frequency or intensity with engine speed originates from either your ignition system or your alternator and is transmitted via your antenna. If it's a crackling sound, the source is your ignition system (coil). If it's a whining sound, the source is your alternator. Both should/can be fitted with capacitors to suppress/eliminate the interference. You could certainly replace/add a capacitor on the guilty source to deal with your problem. I have no idea what kind of uF spec you need.
 

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Both your ignition coil and alternator should already have their radio frequency interference suppressed by a capacitor wired in parallel from the positive side of the power supply to ground. In this way, the capacitor will pass A/C (interference) to ground but block D/C so the performance of the component that is being suppressed won't be affected.

Capacitors can be mounted internally to the component or externally. If mounted externally, the capacitor can obviously be replaced quite easily. A capacitor mounted internally will require you to replace the component unless you're a geek and it doesn't sound like you are. It's not uncommon to find external noise-suppression capacitors mounted on the inner fender wells (my truck has them but I don't recall seeing any on my Escort). Sometimes there is one hanging off the primary side of your ignition coil. Ensure there is a good connection on each side of the capacitor. Considering your problem is intermittent, I'd be checking for good connections and grounds.

The first thing you need to do us determine which source is causing the interference, as per my earlier post. This will narrow down your search and allow you to select an appropriate range capacitor if replacement is needed. It could be just a diode gone bad in the alternator as well. You need to do some troubleshooting or find an electronics geek to do it for you.

Good luck.
 

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Discussion Starter · #9 ·
hmmm, im wondering about a ground. I remember working on my car a while back and finding a detatched ground somewhere... well broken really, and I dont think I remembered to fix it. I took a look in the dark tonight, and didn't see it, but maybe that's it. Do you have any suggestions where to look?
 
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