Audio Tach
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Joined: Mar 2008
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From: Near Los Angeles
Audio Tach
Does anyone know how to get rid of the engine noise coming thru my radio, even when the radio is 'off'?
I have a 1975 F-250, and recently converted to a late model ('94) high amp alternator and MSD ignition with an MSD TFI coil. It sounds like the heater fan is running, but it is not. The sound is coming thru the speakers.
Cheers.
I have a 1975 F-250, and recently converted to a late model ('94) high amp alternator and MSD ignition with an MSD TFI coil. It sounds like the heater fan is running, but it is not. The sound is coming thru the speakers.
Cheers.
Posting Guru
Joined: Jan 2005
Posts: 1,299
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From: The Vieux Ford, Kansas
You need to run plug wires with RF surpression. The high voltage discharge will create a radio signal that will create a pop when each plug fires, and you get to listen to a very annoying buzz. Pulling power directly off the alternator for your head unit can cause this too but is much less common.
-Johnboy
-Johnboy
Elder User
Joined: Jul 2004
Posts: 911
Likes: 2
From: Northern Virginia, USA
Spark plug wires shouldn't be creating enough RFI to drive 4-10 ohm speakers all by themselves- (you'll hear from the FCC if they are!). I've heard spark-plug/radio interference before- but that's coming in through the antenna and high-impedance input stages on the amplifier as broad-band RF.
If you had a bad ground somewhere, or a partial short, or mixed up wiring somewhere, or a partially bad alternator regulator, or bad winding on the alternator, that would be more believable. Turning your radio off disconnects input power to the amp circuit (although perhaps "only sort-of" on modern radios that have a "power/standby" button instead of a physical off switch), but doesn't disconnect ground. If your ground "voltage" (supposed to be 0VDC) were "fluctuating", it could be back-feeding into the amplifier output capacitors, causing current to flow through your speakers.
Easy summary: I think you should double-check your wiring and test the alternator & regulator.
With the engine running, grab a multimeter and you should see about 13-14VDC from your alternator, and 0VAC. If you have any sort of AC voltage beyond a few millivolts, I'd suspect the alternator and/or regulator.
If you had a bad ground somewhere, or a partial short, or mixed up wiring somewhere, or a partially bad alternator regulator, or bad winding on the alternator, that would be more believable. Turning your radio off disconnects input power to the amp circuit (although perhaps "only sort-of" on modern radios that have a "power/standby" button instead of a physical off switch), but doesn't disconnect ground. If your ground "voltage" (supposed to be 0VDC) were "fluctuating", it could be back-feeding into the amplifier output capacitors, causing current to flow through your speakers.
Easy summary: I think you should double-check your wiring and test the alternator & regulator.
With the engine running, grab a multimeter and you should see about 13-14VDC from your alternator, and 0VAC. If you have any sort of AC voltage beyond a few millivolts, I'd suspect the alternator and/or regulator.
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Khauler
1967 - 1972 F-100 & Larger F-Series Trucks
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Jan 31, 2011 10:28 PM
