1994 Chevy Truck Ignition Noise - RFI Forum at eHam.net

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eHam.net Forum : RFI : 1994 Chevy Truck Ignition Noise

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1994 Chevy Truck Ignition Noise	Reply
by N5IPT on July 1, 2008	Mail this to a friend!
I saw another thread that detailed a 1997 Chevy Truck. Lots of good suggestions there, but I just wanted to get an opinion to see if my situation seems any different. First, the noise is only when the engine is running. If a repeater is sending the carrier tail, I can hear the noise. In extreme cases the noise comes through the FM transmission, sometimes to a very disturbing extent. It's a popping/buzzing sound that changes frequency with the engine RPM's. I have tried the following: * Grounding the radio power directly to the battery (was only to the body before.) * Grounding the tailpipes at different points to the battery itself. I have also taken my H.T. with the ducky. I do hear noise when it's near the tailpipes mid-section. Further, there is noise around the spark plugs. However, the MOST noise seems to come from the ignition cap/rotor. The cap and rotor is mainly made out of plastic. The spark plugs/wires are about 3 years old. The cap/rotor is at least 5 years old. I see racing wires for about $250 a set - but I don't see how more conductive/thicker wires will eliminate noise. (It would only create a thicker antenna to radiate RFI!) Do you have any suggestions on things to try with this particular situation?

RE: 1994 Chevy Truck Ignition Noise	Reply
by K7KBN on July 1, 2008	Mail this to a friend!
Disconnect the antenna and see if the noise goes away or decreases significantly. This will tell you if it's coming in via the antenna, or via the power leads. Different entry point, different tactics. 73 Pat K7KBN

RE: 1994 Chevy Truck Ignition Noise	Reply
by N5IPT on July 29, 2008	Mail this to a friend!
Disconnected antenna. No noise. It only seems to appear over modulated carriers. It is worse for distance FM stations. This also effects my broadcast FM radio slightly. The higher power and better the signal, the less of a problem this noise is.

RE: 1994 Chevy Truck Ignition Noise	Reply
by K7KBN on July 29, 2008	Mail this to a friend!
Try taking a shirt-pocket size AM radio, tuned in between stations, to the truck. With the engine running, and being very careful of all the rotating machinery, hold the radio near the alternator, the fan motor/blower motor, wiper motor - all electrically operated equipment - and notice where the noise seems to be centered. Youmay need to get some disc ceramic capacitors, rated somewhere around 0.05 to 0.1 uF @ no less than 50 volts. Most of them will be 200 volts or higher, which is fine. The idea is to bypass the interference to ground via one or more of the capacitors. There are other ways to "sniff" for noise, and I'm sure others will be adding their advice. Good luck; this is one of the more mind-numbing phases of mobile radio. 73 Pat K7KBN

RE: 1994 Chevy Truck Ignition Noise	Reply
by K7KBN on July 29, 2008	Mail this to a friend!
Forgot to mention: consider replacing plugs and plug wires with resistor-types. Probably no need to get the "racing" variety, but the resistor wire/plugs do affect the noise level. Did you replace the cap and rotor as mentioned in the first post? Don't forget the "condenser". 73 Pat K7KBN

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