New Old Guy in Kentucky

PistolGrip · May 24, 2022

I bought my son's very low mileage '94 Cobra in 2000 when he got married. He is still married & I still have the Cobra, so win-win!
It now has 77,000 miles on it & still looks pretty good!
There are a few questions I have & this looks like the place where I might find the answers. I'm low-tech, so bear with me.
For the past couple of years (I don't rush into things) my (stock) radio will occasionally develop a loud buzz. I can tell it is the engine cylinders firing because I can speed it up by revving the engine. It will ONLY buzz when the engine is running & it comes & goes without warning. The buzz (when it is in that mood) works in all modes...AM, FM, CD & tape. I've removed the radio & I don't see anything loose or....
I believe that white plastic thingy with the 4 wires (2 black & 2 red) is some kind of filter. I was considering replacing that....but I don't know if it's the culprit....and actually, I don't even know what to call it. I did check the radio-related fuses & they're all good.
Anyone heard of a mysterious off & on radio buzz?
Thanks

Ronnied · May 24, 2022

Not a audio guru but if it is a Cobra it should have the Mach sound system. Sounds like an amplifier issue. Hell could be a ground issue, but I'm leaning towards th Ed amplifier.

Ronnied · May 24, 2022

Auto correct.....the amplifier

ttocs · May 25, 2022

not sure if its a noise filter or not but I would not start there. Look under the hook on the ignition coil and there should be a small little can-shaped piece with a single wire attaching to a harness hanging off of the coil. That is an ignition noise reducer I believe is called an ignition condenser and is responsible for removing the ignition noise that can be picked up by other electronics especially the radio. Check the harness on it(remove, clean and then plug back in) and see if it makes any difference to the noise if you mess with it while the motor runs. It is just a capacitor and they are known to go bad eventually.

PistolGrip · May 25, 2022

Thanks for the sudden replies. It is a Mach sound system. I'll follow through on your recommendations and let you know when I locate the culprit.

ttocs · May 25, 2022

PistolGrip said:
Thanks for the sudden replies. It is a Mach sound system. I'll follow through on your recommendations and let you know when I locate the culprit.

what part of Ky? I am just north of the ohio river and look forward to hitting bowling green in oct for NMRA

96blak54 · May 25, 2022

Im central Ky. 10minute drive south of Frankfort

PistolGrip · May 25, 2022

ttocs said:
what part of Ky? I am just north of the ohio river and look forward to hitting bowling green in oct for NMRA

I'm in Northern KY....Park Hills. I'm going to Bowling Green in mid June for the Hot Rod Reunion.

tinnocker · May 26, 2022

About 2 years ago I bought a 68,000 mile 94GT. It had the same problem. and I think I posted about the problem and tried some of the previous things mentioned with no luck. Mine was not a minor hum but a roar that came on randomly, sometimes the radio would play normal but when it would roar, I would jump out of my seat. It may have been ttocks that told me to take the drivers kick panel off and the plastic strip running down the door entrance. Then pull the carpet back and look at the wiring. I did that but could see nothing, but I moved them around while checking everything out. I put it all back together, thinking that I wasted my time but the roar was gone. I hope this helps you.

PistolGrip · May 26, 2022

Being a 'newbie' here, I didn't see your previous post. Strangely, several years ago I was backing out of my driveway and when I went to go forward, putting it in first gear (5 speed) there was a LOUD noise that came from the radio (amplifier?). It was just for a second or two...and I don't recall ever hearing it again. My occasional buzzing is totally different...clearly static from the engine...cylinders firing. That one loud noise from a few years ago has never returned (I probably shouldn't have said that)

ttocs · May 26, 2022

you guys are just looking at it all wrong. If its a racecar you have an audible tachometer to help you to know when to shift.

PistolGrip · May 26, 2022

No race car...pure bone stock. But when the car gets in this 'mood', the sound is clearly the speed of the engine firing.
The 'mood' has mysteriously come & gone over the years, with no pattern of warning either way. The only way to be certain of avoiding the noise is when the radio is on without the engine running (either on accessories or the key on - but not yet turned to 'start'). I'll eventually find the culprit! I was hoping someone else has had the same experience and has won the battle.

Wood's 5.0 · May 31, 2022

Hello and welcome to the forum. I had a similar issue when mine was new. The hum coincided and matched the RPMs. The higher the revs, the higher the pitch of the hum became. It developed shortly after I bought it in 1995. IIRC, it turned out to be a ground issue. Again, IIRC, the tech told me there was a TSB out on the early MACH systems for this issue. Lord, that has been a lifetime ago but I want to say he added an additional, good ground and I never had the problem again. My memory is the second shortest thing I have (I forgot what the first one was) so maybe they had to replace the harness but I don't think so. Sounds like the same thing happening with yours.

PistolGrip · May 31, 2022

Well, misery loves company, so I'll find some modest comfort it finally hearing from someone who has actually experienced my problem. I have chased some grounds & cleaned them up - even in one case where I thought I had solved it (on the radiator support near the battery). Sadly the problem returned a couple of weeks later.
I may start searching for 'antique' TSBs - or old mechanics who have not yet lost their memories.

If you happen to wake up in the middle of the night with more about your experience....or where your offending ground was located)...please let me know - at a more reasonable hour.

Thanks

Daryl · May 31, 2022

Welcome to The Forum from the Left Coast! I like your sense of humor already! You’ll fit in just fine around here. TONS of great and very knowledgeable/helpful people here.
As far as the stock stereo. Shit wears out! There are places that will swap out: you send yours; thru send you a remanufactured replacement.

I opted to upgrade to a double din head unit and speakers but kept the Mach460 setup. I also kept the stock radio in caseI sell the car and the newby wants OE.

Choice is yours…

PistolGrip · May 31, 2022

I wouldn't mind replacing the whole thing if I thought that would do the trick. While I'll admit to not being a 'radio guy', I have trouble believing my problem is in the radio, since it (AM & FM, CD & cassette) all work perfectly when the engine isn't running. And even when the car is running it works 1/2 the time....in totally unpredictable intervals...sometimes weeks at a time....and in all kinds of weather....then the buzz of engine interference rears its ugly head.
Along with a stubborn tree stump in my yard, I'm gonna battle BOTH of these annoyances until I win out...or die trying. Tat's what we curmudgeons do.