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2001 Chevy S10 Interference Issue

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jfhtm350

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I have a RS Pro-164 handheld scanner. When the truck is running im getting what kind of sounds like alternator whine coming through. You can rev the engine up and hear the interference sound like it. I dont have to have the power plugged in (is running on batteries) so I know its not coming in through the power wires so it has to be coming in through the antenna. I have tried another antenna and also another scanner and the same thing.

I am assuming its coming from the coil, wires, or cap or possibly the alternator via frequency. The ignition system is the HEI ignition. When i put the scanner on the CB band it does not do it at all. Clear as a bell.

Around 460 mhz, on FM mode with the squelch all the way down, when someone keys up the interference comes in but not if no one is talking. If I put it on AM on the same channel, the interference comes in whether someone is talking or not with the squelch all the way down.

Maybe someone has had this issue before and knows where the problem is or how to troubleshoot and isolate the problem. It is so bad that you can barely stand to listen to the scanner because it is so annoying and drowns out what is being said.
 

B_Mitchell

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check to make sure there isn't any corrosion on the battery terminals,
I was having a simillar problem.
Cleaned off the battery terminals did the trick.
 

CCHLLM

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Is it a high pitched whine or a buzzing sound whose frequency varies with engine speed? Do other cars cause the noise problems in the radio?

The buzzing is probably ignition system noise. The varying medium to high pitched whine is alternator noise. Ignition noise is radiated noise and is only cured by putting good wires and parts in the ignition system. If you're getting radiated alternator noise, the diode bridge in your alternator is probably on its way out, especially if the alternator has a lot of age on it, and the vehicle wiring becomes the transmitting antenna for alternator noise.

Bad connections don't have to be visible to the eye for there to be a corrosion problem, so check those, too. I'm sure someone will suggest some hinky snake oil hack cure like putting an external filter on things instead of actually addressing the real problems. External filters are nothing more than band-aids on an open fracture and never do anything more than cover up the real problems, and while they can attenuate some line noise in the DC wiring side, they will never stop radiated noises completely. We always referred to that kind of hack solution as the "Radio Shack approach".

Take it somewhere that can test the alternator and see what gives. Most auto parts houses can put a meter on the alternator and tell you what kind of shape that's in and whether or not the diode bridge is suspect. If the bridge is bad, the alternator will fail sooner or later, most likely sooner, so replace the alternator. Sometimes the problem can be the vehicle computer. That usually has different characteristics, and some shielding on the main computer cabling can help but probably won't cure it.
 
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jfhtm350

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Its a medium pitch i guess that varies with engine speed. Ive tried the scanner in a couple of other different vehicles and its good and clear.

I think im going to pull the accessory belt off and crank it up and see if that helps it any. That way the alternator will not spin. I dont remember ever having to change the alternator and it says delphi on it so it has to be the factory one so it may be ready to take a dump on me like you say.
 

jfhtm350

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Ok this is what i found:
Pulled off drive belt and cranked. Still the interference.
Unplugged the coil and cranked. Interference gone. Coil not firing.
Unplugged the coil wire from the distributer cap and grounded the coil wire to the engine with a jumper wire. Interference gone. Coil firing.

The problem lies within the plug wires or distributer cap. Does anyone recommend a known set of wires that is shielded good? Have a set of Bosch Ultra Premium on there now, but are 12,000 miles old. Plug wires could have a crack or something in them also or the exhaust manifold has burnt a hole in one.

Got the scanner this past Christmas and the noise has been in the vehicle since then but i dont know about before so I dont know if i want another set of Bosch wires or not.
 

Essexscan

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Could also have a bad Sparkplug too, The "R" in the plug code stands for resistor. this is for radio noise also. most newer car have enough shielding in the factory radio and chokes in the wiring that will shield the radio even with a bad plug. If you going to do the wires and cap&rotor throw plugs in it too Get GM performance wires and AC/Delco cap-rotor-plugs. the factory cap&rotor are good there's a reason HEI was around so long
 

jfhtm350

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Yes I am researching some of this stuff right now. Haynes manual says stock plug is AC 41-932 and AC Delco website says 41-993. Seems like everytime you change a plug they change the numbers on them for whatever reason.

Where do you get the GM performance wires at? Seems like the AC Delco wires have alot of RFI resistance built into them when reading the features and benefits tab here:
ACDelco OES Ignition Wire Sets
Ignition Wire Sets | ACDelco
 

Essexscan

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Yes I am researching some of this stuff right now. Haynes manual says stock plug is AC 41-932 and AC Delco website says 41-993. Seems like everytime you change a plug they change the numbers on them for whatever reason.

Where do you get the GM performance wires at? Seems like the AC Delco wires have alot of RFI resistance built into them when reading the features and benefits tab here:
ACDelco OES Ignition Wire Sets
Ignition Wire Sets | ACDelco

SummitRacing.com they stock all GM ac/delco and GM performance parts. Spark plug numbers change daily there are always supersedences and alot of plugs are interchangable most of the time is a change of the plug heat range for emmissions
 

CCHLLM

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Wow, good troubleshooting. I'm lazy - I would have unplugged the alternator. :D The only other thing I could think of that occurred to me today is if it has multipoint fuel injection, the injectors operating can produce a noise very similar to ignition noise, and if it has throttle body injection, it will sound like alternator noise played on slow speed, but it wont necessarily follow engine speed. With all that said, it looks like you've narrowed the field of possibilities pretty well so far.

Noise suppression is a two edged sword. It's a balance between suppression and energy transference, so if you order the wrong type of performance ignition components, the noise suppression may only be adequate in the narrow bands of AM and FM broadcast radio, and outside of that it may be as bad as no suppression at all. Read carefully as to the radio suppression claims and specs of the products.
 

jfhtm350

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Problem found and fixed.
The graphite ball in the distributor cap that contacts the center of the rotor button was wore plum out. It actually fell out when i took off the cap. Truck was not missing any so the voltage was jumping the gap. Looks like it would have lasted longer than that.
 
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