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Radio Noise 1996 Cadillac Sedan De Ville On AM
Sent to Car Experts May 23 05:42 PM

On AM I get a constant noise on my AM radio if the car is moving over a few miles an hour. When sitting still there is no noise and the radio is clear. I can race the engine if the car is stopped and there is no noise. It is only when I am moving. If the car is just barely moving the radio is clear.

Customer (name blocked for privacy)
Status:  Closed   Value: $5
Answer
May 23 5:49 PM (7 minutes and 31 seconds later)
         
ACCEPTEDCheck Mark

    This is an interesting condition; most radio noises originate in the ignition system or in the electric fuel pump circuit.     It would be interesting to know if the interference is present with the ignition on, engine not running, when coasting a long distance?     My thought is that the car may be building a static charge that could interfere with radio reception; if so this could be due to the tires.   Some brands of tires do not ground the car as well as others.  Perhaps installing one of those chassis ground straps that hangs under the vehicle and makes contact with the road surface may help.    Maybe temporarily installing a copper wire to drag on the road from some good ground point on the body may be an interesting test (carelul to keep it away from an axle or brake lines where it could cause damage if it got tangled)

   If anything else occurs to me, I'll let you know...

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Steve7654 -- Auto Service Technician -- 99% Positive Feedback on 1726 Car Accepts
27 yrs ASE L1 Master Technician, Service manager
Answer
May 23 5:53 PM (3 minutes and 33 seconds later)
         
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Steve7654 -- Auto Service Technician -- 99% Positive Feedback on 1726 Car Accepts
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Info Request
May 23 6:31 PM (38 minutes and 30 seconds later)
         
REPLIED to Info RequestCheck Mark
 You could probably do a lot better with a high quality set of ignition wires. If they are old, the resistence is high and they are very leaky. Accelerating increases the KV and that is probably why it gets louder.
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Tech501 -- Auto Service Technician -- 96% Positive Feedback on 740 Car Accepts
38 years exp, ASE Mastertech with L1 Advanced Engine performance
Answer
May 23 6:52 PM (20 minutes and 33 seconds later)
         
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Steve7654 -- Auto Service Technician -- 99% Positive Feedback on 1726 Car Accepts
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Info Request
May 23 7:01 PM (9 minutes and 20 seconds later)
         

 

Quote:
The customer states that revving the engine sitting still does not make the noise occur, so that would tend to discount ignition wires as a culprit.

Quote:
Perhaps, sitting still with the car in gear and your foot on the brake, and accelerating to load the engine may be a useful test here.     That would induce the conditions to generate high firing KV, without the vehicle being in motion.    If this causes the interference to happen, then an ignition component such as a wire, cap, rotor, or spark plug may indeed be at fault.

OK, which is it? the first statement disagrees with me and the second agrees with me.

If it only happens under acceleration it's KV leakage in the ignition wires.

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Tech501 -- Auto Service Technician -- 96% Positive Feedback on 740 Car Accepts
38 years exp, ASE Mastertech with L1 Advanced Engine performance
Reply
May 25 7:58 AM (1 day and 12 hours later)
         
Reply to Tech501's Post: it not a matter of getting louder. There is NO noise in AM when the car is parked. It does not matter if the engine is running. You can idle the engine or race the engine and there is no noise. As soon as the car begins to roll (over 3 or 5 miles per hour) the static will become loud enough to knock a station off the air.
It is the movement of the car and not the engine that creates the static.
Customer (name blocked for privacy)
Answer
May 25 6:07 PM (10 hours and 9 minutes and 10 seconds later)
         
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Tech501 -- Auto Service Technician -- 96% Positive Feedback on 740 Car Accepts
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