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My 1998 Silverado, with an after-market (Sony) head unit, has developed quite a bit of EFI (on AM) over the past few years. I replaced the spark-plug wires with OEM ones last month, but the problem has not been solved. The disturbance occurs only when the engine is on. Once in a while, the turn indicator sound will come through (just a little) plus I can hear the engine rev's in the EFI as well. I've had the truck for ten years, and it has about 112,000 miles on it.

What should this non-mechanical man do from this point?

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Since it is doing it on AM, I would suggest making sure that the antenna is grounded. The car is a few years old and the antenna mount may have loosened and degraded the grounding of the antenna. If possible, take the antenna off of the fender, clean underneath it and reinstall, making sure it is good and tight. That has eliminated AM interference in my cars when the interference developed over time.

This sounds absolutely daft, but it works. I've used it to get EFI out of radios, guitar amplifiers, and other appliances.

Take the +12 lead coming from the fuse box to the power input on your radio (hopefully you have an in-line fuse in addition to the car's fuse box, just for safety) and lenghten it. That's right: solder in about two to three feet of wire to it, and do the usual black tape or shrink wrap to insulate the joints. Then tune it in to something that you notice the EFI really prominently. Then make a single loop out of the power lead, starting with a couple of inches in diameter, and gradually increasing the diameter until the EFI goes away. Then tape the loop at that diameter and make sure it lays flat under your dash or on behind the console, however you have it hooked up, so that this diameter loop can stay constant. This will "tune" the power circuit and provide a "trap" for the EFI.

One time I had a guitar gig and my Marshall amp started picking up the local radio station so loudly it sounded like I had turned on a radio. I took a longer guitar cord than I usually use, plugged it in, and since my amp was on a stand, took velcro, made this single loop, and worked it back and forth until the EFI was eliminated. Then I took the velcro strip, secured the loop to the bracket of the amp stand, and the amp was quiet for the duration of the gig.

Give that a try for sure.... Couldn't hurt and it isn't hard to do.

I suggested the grounding thing because the radio worked fine at one time.

Report back with what works...

Jeff "Waiting to hear from the Resident Genius" Benedict

It could also be grounding. Bad grounding can do really wierd things.

Thank you for the suggestions. I will attempt the least challenging, as far as my abilities go, and perform the antenna thing offered by brother Benedict. Will keep y'all apprised.

David "occasional Master of Disaster" Gilbreath