Engine bay buzzing noise

[Bronco808]

Hi all, I just got my wife's 1973 Bronco running and it just started this weird buzzing sound. I've run it with all the fan belts off and checked all the vacuum lines. The sound doesn't speed up or slow down with the engine RPMs either.

I just can't figure it out.

Here's a link to a short video of it.

Thanks in advance and aloha!

 

[thegreatjustino]

Get a long piece of rod or stethescope, put them up to your ear, and pinpoint the noise.

Sounds to me like the harmonic balancer is rubbing on something or the rubber dampener inside it is failing or has failed.

 

[DirtDonk]

Electric fan maybe? Can you easily unplug it? Or just verify that it's not spinning when the sound is happening?

Since it does not follow the speed of the engine, then it "should" not be the damper, or even something inside the distributor (sounds almost like an electric arc), but can you scan around the engine bay fully so we can see what else is under the hood?

Dolphin stuck near the hot exhaust?

Good luck. Definitely do the stethoscope thing like Justin suggested.
You can often do the same thing with a sufficient length of rubber hose.

paul

 

[Bronco808]

Electric fan maybe? Can you easily unplug it? Or just verify that it's not spinning when the sound is happening?

Pulled the fuse on the fan and no joy

Since it does not follow the speed of the engine, then it "should" not be the damper, or even something inside the distributor (sounds almost like an electric arc), but can you scan around the engine bay fully so we can see what else is under the hood?

Pulled the HEI dizzy cap and didn't see any rub marks

Dolphin stuck near the hot exhaust?

No dolphin either ;D

Good luck. Definitely do the stethoscope thing like Justin suggested.
You can often do the same thing with a sufficient length of rubber hose.

I have one of those I got from Harbor Freight. Tried checking all over the engine and tranny and couldn't pinpoint it. I'll try again today when I get home from work though

paul

Mahalo Aloha!

 

[blubuckaroo]

PCV valve?

 

[Madgyver]

Need help brother? Hit me up.
just saw the video.
No change with sound at different rpm?
you got me....

spray wd40 or carb cleaner around base of carb or anywhere there could be a vacuum leak with motor running.

 

[Slowleak]

Check your PCV valveÂ…..

 

[Bronco808]

Need help brother? Hit me up.I just may take you up on that! I have a fully restored 66 Mustang with a full roller 347 and this has me stumped
just saw the video.
No change with sound at different rpm? Nope stays at that constant speed/tone/sound, weird right
you got me....

spray wd40 or carb cleaner around base of carb or anywhere there could be a vacuum leak with motor running.I checked all the vacuum ports and they seemed OK but will try this next

Forgot to add, the sound didn't start till after I had to add 4 quarts of type F trans fluid and was able to get her to move forward/reverse and no, she's not overfilled haha

Much mahalo and aloha!

 

[Bronco808]

Check your PCV valveÂ…..Hmmm going to try and pull the valve and get back to you

Mahalo and aloha!

 

[jerry]

Man, that thing is obnoxous!
But it does change pitch between beginning and end of the video

Voltage regulator?
A stretch, bur maybe: Remnants of an old alarm system? kinda sounds like this:

Welcome aboard and good luck!

 

[Bronco808]

Man, that thing is obnoxous! RIGHT! LOL
But it does change pitch between beginning and end of the video I suppose it does a bit but not really noticeable while I drive or rev the engine

Voltage regulator?It's brand new but I tried tapping it with a screwdriver
A stretch, bur maybe: Remnants of an old alarm system? kinda sounds like this: She never had an alarm. I bought her from a friend who got too deep for himself doing a painless wire harness change and just let her sit for 2 years

Welcome aboard and good luck!

The only thing I can recall doing before it started that infernal noise was adding 4 quarts of trans fluid, yes she was that empty.

Thanks for the response! Aloha!

 

[DirtDonk]

Was going to say look around for an air compressor. Maybe there's one underneath a fender. But an old alarm is even more likely.
Unplug the horn as well. It's usually down in the front driver side corner. But if you don't see one, look around.

 

[DirtDonk]

I had what I assume was the pump in my C6 making noise one time after I started it up. I shifted it through the gears and it changed. Then I turn the engine off and restarted it and the sound was gone.
Have you run it through the gears yet?

Mine wasn't low on fluid, but your mentioning that made me think about the one time my transmission made a loud screeching sound.

 

[jerry]

Was going to say look around for an air compressor. Maybe there's one underneath a fender. But an old alarm is even more likely.
Unplug the horn as well. It's usually down in the front driver side corner. But if you don't see one, look around.

By any chance could it be an electric fuel pump? I wonder if underneath the truck would provide any clues.

 

[Bronco808]

I had what I assume was the pump in my C6 making noise one time after I started it up. I shifted it through the gears and it changed. Then I turn the engine off and restarted it and the sound was gone.
Have you run it through the gears yet? Yup, drove it around the block a couple times and it shifts OK too.

Mine wasn't low on fluid, but your mentioning that made me think about the one time my transmission made a loud screeching sound.

Thanks again!

 

[Bronco808]

By any chance could it be an electric fuel pump? I wonder if underneath the truck would provide any clues.

Nope, it has an mechanical pump and seems to be isolated to the engine bay area, just cant pinpoint where exactly.

Thanks again!

 

[73azbronco]

Does not change sound when revved, even in gear? That to me would probably discount the C4.

 

[Bronco808]

I spoke with and showed the video to our GSE mechanic at work. He watched it a few times and said it sounds like a vacuum leak (whoa). When I got home I started spraying carb cleaner at all the vacuum lines and nothing. However, I then sprayed and the base of the carb spacer and it sputtered! I tried tightening the carb down and it helped a bit but it was still buzzing. Put some black RTV and SILENCE!

So I'm guessing, when I changed the accelerator pump and changed the base gasket under the carb spacer it was too thin and blew out after running for a bit. Apparently, there was just enough of a gap for the paper gasket to work like a reed in a saxophone LOL. Now I need to find a thicker gasket but it works for now.

Mahalo to all who replied!

ALOHA!

 

[1970 Palmer]

The carb base gasket "under the carb spacer", and the base gasket "on top of the carb spacer are not always the same shape. I think I would want to take a look and figure out why it was sucking a vacuum leak? It could be as simple as reversing the two gaskets? If everything is flat and clean, it should seal up without any extra sealer.

John