I have a hissing noise on my 88 GXL coming from the dash pod when the tach nears 4000 rpms and keeps hissing till I shift. Once it drops below 4k it goes away. Seems to me as though it didn't happen all summer. Today has been around 45-50 degrees and it's doing it again. I had the heat about half way up. Any help would be appreciated.

 

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Tach is dirty inside... more common on series 4 cars but occasionally seen on series 5.

It won't hurt anything, but if you are really concerned, remove the entire tach assembly from the cluster, and clean it with compressed air and "safe for plastics" spray in contact cleaner ($8 at radio shack).

 

I have that problem too, thanks for the advice Ice.

 

I'll give it a try ! Thanks