Engine Noise through stereo

Your point is valid and my solution was from an actual application where a new radio was installed into a gas vehicle that never had one previously. Noise only came through the radio when the engine was running. When the engine was stopped, the noise was gone when the radio was operating.

You are correct in that the RFI is likely coming into the radio via the antenna. I should have stated that the spark plugs were introducing the noise over the air, not through the power line. I apologize for not stating what was the obvious.

Just the same, the original ground wire was too inductive, causing the radio's reference plane to "float" and the change to the heavy ground strap fixed the problem instantly. Internal to the radio, it is my suspicion that the noisy ground plane is polluting the receiver's oscillator circuits. I have fought this battle several times as a radio designer.

At least there are several possibilities to try out.

fishy68 said

Very good but don't forget RFI as a point of interference introduction. In his first post he said it only comes through the radio. Sounds like that would be introduced through the antenna, instead of the power line. I'm a amateur radio operator (call sign KB9VXQ) and have been in on chasing interference quite a bit whether it be automotive or high tension power lines. I was also an electronics major in college.

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