AM Radio squeals now -- Any suggestions?

[JoeVR5]

Hi all,

I have a 1997 Ranger 2wd v6 4.0 5spd

I listen to AM radio fairly often, and all of a sudden mine started sounding TERRIBLE. Kind of a high pitched whining noise -- really hurts my ears

The FM is fine.

I thought it was my head unit (about an 8 year old Alpine), so I bought a new one (it was actually an excuse to get a head unit that has a plug for my phone), but anyways the AM radio also sounds lousy with the new one too!

It sounds good when the truck is off, but once I start the engine, the AM reception is terrible. FM is fine.

Any help would be greatly appreciated. Thanks everybody

 

[adsm08]

Sounds like you have an RFI issue.

I'm betting that your RFI capacitor on the coil pack is toast. It's a cheap part, easy to replace.

The only other thing to really try is unhooking the alternator and starting it up, make sure that isn't the source of your RFI.


We have had trouble looking up those capacitors by going under the Ranger lately, but the ones for the F-150 5.4L are easy enough to find, and it's the same part.

 

[4x4junkie]

Does the squeal vary widely in pitch with engine RPM? Or is it fairly constant? Does the squeal occur on all frequencies (channels)? Or do you hear it only on some frequencies and not on others?

Answers to these should help narrow it down... Some are caused by what adsm mentioned, though others have different causes (power amps and adapters like a USB/cell-phone charger can be culprits as well).

 

[JoeVR5]

The squeal doesn't vary too much with the engine rpm. But sometimes it sounds like it does -- very very high pitch.

I had my alternator rebuilt about 6 months ago -- I'm wondering if that had anything to do with it.

I am going out now to start the truck with the alternator unhooked -- to see if it still causes the AM radio to squeal. Will report back soon. Thanks!

 

[JoeVR5]

Also, Is the RFI capacitor on the coil pack something I can buy at O'Reillys or NAPA?

 

[adsm08]

Probably.

I replace the little guys every 5 years or when I think they have an issue. Like I said, they are pretty cheap.

 

[JoeVR5]

UPDATE:

Sorry -- this is becoming pretty peculiar. For the past two weeks I was convinced that the AM radio interference was from the alternator, but now I am beginning to think that it is power lines. I live out in the country and the power lines follow the roads.

I took the truck down the street testing my new radio and turned around in a parking lot. When I turned around, I drove around a big fluorescent Budweiser sign and the radio went nuts with static.

I also have a 1990 F250 and it does fine with no static or feedback in these places.

I even have bad static in my garage (a simple pole barn). I shut down all the circuit breakers and it still buzzed with static.

Is there any way to address this odd static with my 97 Ranger?

Thanks!

 

[adsm08]

Swap the antenna from the F-250. See it things improve.

 

[ab_slack]

Is this a new radio or one that has been working fine for some time and just now has issues?

A newly installed radio alternator whine is a very likely cause. I have issues in my 87 BII when I plug into cig lighter. Something new may just be reacting different than what was before. All depends on how good the internal filtering is.

Also a lost power return for the radio can be a problem as well. As I recall in the radio wiring harness there is a return. If that opens up the return goes thru the chassis and it will be much more noisy.

AM antennas are usually little wound affairs internal to the radios (or immediately on the back) while the typical whip is for FM. I don't know if the whip antenna has anything to do with AM in the cars or not. So not sure if swapping will make a difference for AM.

AM in general is very susceptible to local noise. If not an alternator noise it could be ignition noise. The easiest check is to have vehicle someplace where you experience this noise. Turn off the engine and put key to acc. Without engine running do you get the noise? If so then it isn't ignition or alternator. To eliminate alternator run engine without alternator as previously suggested and if you hear the noise only when running then you know it is ignition.

I had a small crack develop in the ignition coil insulator on the underneath side of the output electrode. It didn't affect how my BII ran, but it cause ignition noise on AM. particularly when it was very damp out. Also, for some odd reason, when I turned left it was far worse. Eventually it affected operation and when I pulled the coil off I found a big area of the insulator had cracked. Replacing the coil solved both problems.

 

[Mark_88]

Although I haven't actually seen an RFI filter lately, that used to be the biggest cause and cure of "static" on AM radios...and back in the day when I actually listened to an AM radio it was mostly because that was the ONLY option in vehicles...but we're talking about 40 years ago...

I know my Ranger doesn't have an RFI filter on the coil currently and I'm pretty sure that there is static on my AM radio...especially under power lines...

Never bothered to fix that...only thing on AM that I would want to hear is the hockey games...

 

[JoeVR5]

UPDATE:

Okay, I have finally narrowed down the problem, but I don't know the solution.

The AM radio works perfectly fine when the key is turned backwards in the accessory position, but when I turn it forward to the ignition position (without starting it), the static is terrible. (It's also terrible when I start the engine, but it doesn't really fluctuate with the RPMs)

What could this be? Any ideas would be greatly appreciated.

Joe

 

[JoeVR5]

AHA!

I did some more research and it looks like I'm getting RF Interference from my fuel pump.

Just found this page and it includes my 97 Ranger.

http://www.arrl.org/files/file/Technology/tis/info/pdf/W1MG.pdf

I looked up the part and its discontinued. Are there any other ways to remedy this fuel pump radio interference?

 

[LIMA BEAN]

Swap the antenna from the F-250. See it things improve.

The mast antenna should be for frequency modulation (FM) only, for amplitude modulation (AM) it should recieve from an internal ferrite rod with isolated copper wire windings around it. Make sure all is grounded good.

 

[4x4junkie]

AM vehicle radios do infact use the antenna outside (a ferrite rod inside the unit would just be shielded by the metal vehicle body). You're thinking of small portable radios like a boombox.

Fuel pump does sound like a very good possibility here, though I would have to wonder if maybe it's on it's way out if it's making a bunch of noise (it's noise pitch would barely change ever so slightly when you change the amount of throttle you give it).
A good test for it is to turn the ignition on, but don't start the engine. If the noise is present for a second or two then goes off, it's the fuel pump.

On mine I put 0.01µF disc ceramic capacitors across all the wires right where they come out from the pump/sender unit. I did this to eliminate interference to my CB though, there was never a problem with AM radio reception (and is why I say maybe yours might be going out... I've seen a bad blower fan motor cause massive radio interference, then a month or 2 later it quit working).