I know what you guys are all thinking...no its not the redline warning buzzer, lol. git a customer car in for a carb rebuild and when I started the engine today, I noticed that tach making an odd buzzing noise.. 34 RX-7's over the last 14 years and this is a completely new issue I have never seen. I called the customer and he said he has been living with the issue for years. Looking for a little guidance on getting the issue resolved. car is an 84 GS with 31k miles. here is a link to a video of the issue:

video-2013-09-19-16-43-18.mp4 Video by mazdaverx7 | Photobucket

 

I'm wondering if the issue is within the tachometer itself or the signal feeding the tach.. something to look into.

 

That sure sounds like a mechanical sound. Like something winding up. It sure would be an easy thing to test. Just disable the signal to the tach.

 

this is true. I have another tach I can swap in as well, just to test things. can't hurt.

 

going to dig back into this tomorrow and see what i can find out

 

i'm wondering, after doing some testing, if the noise is caused by the original wires that are on the car. they are the original Yakazi wires. I have a set of NGK wires i can try and report back.

 

Hmmmm....

How exactly are you sure that buzz is coming from the tach?

An rpm-dependent buzz like that could be generated someplace else (flywheel, fan area, dizzy?) and travel in a way that makes it sound like it's coming from the tach.

Like KC suggests, have you tried disconnecting the tach to make sure it's the source of the buzz? An maybe a good one to see if that fixes it?

 

I will try disconnecting the tach tomorrow and running the engine. the noise is engine speed dependent and can clearly be heard coming from the tach. it almost sounds like radio interference (see above video). the fan is fine, clutch is fine, no engine vibration caused by a loose flywheel or worn engine or trans mount. I replaced the plug and coil wires today and it seemed to help. I heard it when I first started the engine but did not hear it at all after I shut it down and restarted it a few minutes later.