What kind of interference? Static? Whine? Clicks?
Check your radio for good, solid ground and the antenna for good ground of the shielding around the lead in wire. Clean socket where antenna cable hooks to radio. The radio may work OK with a thin "barely there" ground, but it won't be able to block interference. Could also be an alternator going out. They're AC generators that rectify (change) the AC to DC for the charging system. If a rectfier goes out you'll be putting a small amount of AC into the 12V output which could show up as a whine or hum. Could also be a poorly grounded/sheilded ignition box - if you have one. Move or bypass box to see if interference changes. It sounds like your plug wires are OK (doesn't change with RPM) but some ignition boxes put out lots of RF interference. Can you try your radio in another car? Do you get the same problem with a portable radio inside your car? You just have to go down a list of things to rule out until you find what seems to cause it. It's going to be coming from only two places. Through the air - RF interference, or though the 12v power system.
Then it looks like RF interference. Go after the grounds and shielding. How close is the ignition box to the radio? Try to get it at least 2 feet away. Is it and old radio with a new problem or a new radio doing this since it was installed? Is it a cassette or CD/tuner or just radio? If it's a cassette/CD/Tuner and you get the static while listening to a cassette or /CD, I'd be looking at the whole unit as suspect. If you get static only while using the radio, then the antenna looks like the problem. What kind of antenna are you using? If it's in the windshield, check the shielding and connections (under the window trim.) If it's body mounted, make sure it's well grounded at the base and lead-in cable is in good shape.
Yes it's a c/d tuner,and yes it dose it when the cd is in play or radio is on. The msd box is on the front of the d/s inner fender. I also think it is the unit itself. Guess i need to try another unit. Thanks for your help Bill........Ralph
I just install a Kenwood radio and JVC CD changer in my Chevelle. When I play the radio I have static both AM and FM, but the CD changer plays well, no static or and kind of inference. I have a MSD box, wires and coils. Thge box is mounted on the inner front fender. I also have a hide away antenna that suppose to have a booster that is located in the right corner of the windshield. Any body have any ideas?
Are you talking about a retractable power antenna mounted near the windshild or the internal antenna inside the windshild? If you have a newer radio you shouldn't need a booster, unless you live in the boonies then nothing's going to help. I've been really suspicious of ignition boxes getting too close to antennas and/or radios. Also, since they boost the spark voltage and some add multi-spark, along with some low resistance plug wires you end up with a swarm of RF interfence in the area. Check your grounds on the antenna and it's sheilded cable. If you have another car that has a good sounding radio, pull it up near your Chevelle while running and see if it causes problems in your other car's radio. I've been in traffic and pull up next to a fairly potent car and have noticed all kinds of hash getting into my radio. I'd check to make sure you have RF supression plug wires and maybe relocate the MSD box futher away from the antenna.
This is looking like a fairly common problem in this group, so I'll try to do some more research and report back to this forum.
I'm going to throw out a some more questions... and some may seem way "out there", but I'm really puzzled by your problem. Does the static happen when you have the engine NOT running? Do you have proper voltage in electrical system? Can you find a piece of steel or a metal paint can (empty!!) that you can cover the ignition box to see if you hear any difference? Does the static happen all the time wherever you drive or just in certain areas? Do you have a cell phone tower nearby? Do you have a cell phone on when you listen to the car stereo? What about a neighbor with a really big atenna on his roof (Ham radio)? Do you live near an airport or Airforce base? Sorry for so many questions but interference can come from so many sources. I forget, were you able to rule out a defective radio unit? Maybe you could buy a new one to test (carefully!!) and return it - if you have a dealer nearby with a good return policy.
I don't know what I was thinking... you said that the static was occuring when using both the radio as well as the CD player. That rules out RF (coming in the antenna) You more that likely have power supply problems. Either noise is being generated and added to the 12V supply by something in the car (bad alternator or maybe a bad heater fan motor) or filtering is poor coming into the radio that it can't block the usual garbage that can get picked up electrically (EMI - electro-magnetic interference). You said you tried an in-line filer that didn't work.. was that on the antenna or power feed?
Below is a simple filter with a couple capacitors that you could use to clean up the 12volts before it gets to the radio. You would need one filter on every source of power, both the constant 12v and the ignition switched 12v. Also if you are running any separate amps, you would need to filter them, but this should be included in the circuit of a good amp already.
The exact componet values aren't real critical, but the idea is to have the two capacitors acting on different frequencies of interference - sort of both the "highs" and the "lows". Good car audio equipment should have these circuits built-in, but if you live in a troublesome area, sometimes they need a little extra help. BTW - if your ARE running external amps, make sure the lines between the receiver and amp are good'n solid.
I had a similar problem and it was corrected by replacing the spark plugs. I had resistor plugs in the car but for whatever reason when I replaced the plugs with the same exact AC Delco resistor plugs the problem went away. I also have an MSD box mounted under my dash.
A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!