Cadillac Owners Forum banner

Radio Interference/spark plug wires?

1956 Views 2 Replies 2 Participants Last post by  EldoRedo

I just had the plugs and wires replaced on my 91 Eldo -- also had an MSD 6A ignition installed. Now I get very obvious buzzing on the AM (Delco factory)radio frequencies. You can't hear it on FM broadcast stations, BUT: I listen to my XM radio on an FM frequency through a modulator, and the same buzzing is still audible (but much fainter) in the background. I have checked to make sure the wires are seated (at least the ones I can reach).

Any ideas?

1 - 1 of 3 Posts
Several possibilities here. One is grounding of the MSD box; be sure the box has a clean chassis ground at the mounting point. You might also try a redundant ground wire from the MSD box to the engine block. At least try it temporarily with alligator clips and a length of braided ground strap.

Second is the 12 Volt power input line to your radio head unit or receiver might benefit from an RF choke (filter) in series.

What is probably happening is the oscillator in the MSD box is producing a signal that is rich in harmonics and strong enough to make itself heard in the audio path of your system. If the MSD box is metal enclosed (and they were many years ago), you should be able to eliminate the RF being produced in the MSD box by playing with different combinations of grounding or possibly moving the MSD farther away from the radio components.
1 - 1 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.