Miata Mailing List: March 1995, Message #126
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   From: David Hoelscher 
Subject: 2350 RPM rattle and occasional hissing
   Date: Thu, 2 Mar 1995 18:42:14 -0500


What is the chance that the "3500 RPM rattle" happens on other Miatas 
(specifically mine) at ~2350 RPM?  Has anyone else out there 
experienced the heat shield rattle at any other RPM besides 3500?  3500 
/ 3 * 2 = 2333 suggests that this might be harmonically related.  The 
rattle sounds like a buzzer.  This started fairly early at about 7,000 
miles (10,000 miles ago) on my '92.

Also, what might a hissing sound from my engine mean?  My first guess 
was a clogged fuel injector and my second guess is exhaust leakage.  
This didn't start until I had about 11,000 miles on the car.  To test 
the possibility that it is a clogged fuel injector, I ran more than a 
few tanks of supreme unleaded which supposedly has additives to clean 
injectors.  Didn't help.  The hissing only occurs when I accelerate.  
When I ease up on the accelerator it stops hissing.  As far as exhaust, 
I'm not really sure what other indicators to look for, although I never 
actually smell exhaust while in the car.  The hissing doesn't seem to 
be directly related to engine temperature or outside weather 
temperature.  Sometimes it will hiss for a few days and then stop for a 
few.  At this point I suspect exhaust leakage, although I haven't 
started looking for loose bolts or other signs yet.  Anyone else have 
this problem?

Fortunately I still have another year of warranty left so I'm planning 
to have the dealer look at the heat shield and then mention the hissing 
at the same time.

davidhoe@microsoft.com &
not-yet-named Red '92A with a <>< on the back
MCA - Puget Sound Chapter
(my words, not employer's)