Rough sounding engine

[Mark Denovich <mark@domain.elided>]

I hate to play "name that vague engine sound" but I've never had a car 
with rod-knock, piston slap, or a detonation problem, so I lack a 
trained ear.

Here are the symptoms my 164S is exhibiting:

Under load, between 2000rpm and about 3500rpm, the engine has a loud 
sort of diesel-like sound.  The staccato nature seems to suggest that 
just one or two cylinders are responsible for the noise.   At idle, or 
high rpm the engine sounds more or less like my Verde.

Now that I think about it, the nature of the sound is similar to the 
noise my first car (a '80 Cadillac Coupe deVille) made thanks to a loose 
exhaust manifold.

*scurries down to the garage*

So I found that 3 of the nuts were several turns loose.   The bolts 
seemed tight enough.   In the process I answered the question about 
which battery lead to disconnect:  At least one of them.   I forgot 
about re-attaching the negative lead when I did the compression test, 
and nearly soiled my pants when the wrench tapped the positive terminal 
on the alternator.  Duh!   Anyway, I'll cross my fingers that the noise 
was something as stupid as an exhaust leak, but is it ever that easy?

Other things:  Most of the valves were in spec, one was .002" tight, one 
.002" loose.   5 out of 6 recently replaced spark plugs look good, a 
nice light brown color.  One is dark and seemingly wet.   I experienced 
something similar on my Verde thanks to a fouled injector.   So I sent 
the 164's injectors to be cleaned/rehabed.   Before and after flow tests 
revealed no smoking gun.  I did verify that every cylinder was getting a 
good spark.

The big unknown gnawing at my gut, is the great gobs of RTV the previous 
dumbass owner/mechanic used to seal the valve covers.  I have bad dreams 
that it's blocking oil passages, starving rod bearings, and is 
ultimately responsible for the noise.

	--Mark
	http://alfa.denovich.org
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