I would appreciate any suggestions to solve a long time problem with ignition noise on the radio of my rust free 87 Mercury Cougar. I believe it is ignition since it is only on AM and is a popping noise (not whine) which changes with engine speed. I have tried the following:
Subsituted the radio with a known good radio from another 87. Noise still present.
Removed and cleaned up antenna/mount assembly. Continuity tests of the antenna and cable assembly end to end are perfect and at specs.
Cleaned up all ground connections which are scattered throughout the vehicle, inside and out.
Ran a ground wire from radio chassis to known good ground point.
Replaced plugs with OEM resistor, plug wires (motorcraft), cap, rotor and coil. No change.
I even tried installing a couple ferrite units from my computer stuff around the radio harnesses which made no difference.
I know vehicles usually have some kind of noise filtering capacitor bolted to the chassis somewhere but I looked everywhere and do not see one. I was considering installing one off the radio power connection.
Kind of stumped and would appreciate any suggestions. I want to keep the original radio in the car.
Subsituted the radio with a known good radio from another 87. Noise still present.
Removed and cleaned up antenna/mount assembly. Continuity tests of the antenna and cable assembly end to end are perfect and at specs.
Cleaned up all ground connections which are scattered throughout the vehicle, inside and out.
Ran a ground wire from radio chassis to known good ground point.
Replaced plugs with OEM resistor, plug wires (motorcraft), cap, rotor and coil. No change.
I even tried installing a couple ferrite units from my computer stuff around the radio harnesses which made no difference.
I know vehicles usually have some kind of noise filtering capacitor bolted to the chassis somewhere but I looked everywhere and do not see one. I was considering installing one off the radio power connection.
Kind of stumped and would appreciate any suggestions. I want to keep the original radio in the car.