Scott -
I'd bet a dollar your boss' car is suffering from the nose pulley failure
common to early 1.6l Miatas.
Sometime around 1991 Mazda changed the crank's nose pulley and the bolt that
holds it in place to be a larger unit. This is the gear that holds the
timing belt. With the early 1.6l, the bolt can vibrate loose (or be
misinstalled during a timing belt change) and cause the pulley to wobble to
the point of the keyway wearing away at both the crank and the geared
pulley.
When this happens, the static timing at various RPM is fine, but when the
engine is in a transition stage (i.e. semi-acceleration) the timing is off.
You can likely limp along with a JB Weld type fix, but the easiest and
likely most economical fix is an engine swap--preferably to a later 1.8l out
of a 1999-2001.
On Fri, May 29, 2009 at 10:05 AM, <scott.hall@comcast.net> wrote:
> not at all shop related, but it's my boss' car, I'm at work, and I figure
> you guys would be the place for the quick, correct answer.
>
> his 1990 miata has an off-idle/tip-in 'miss' (I think). it idles okay, and
> at full throttle, it sounds and seems to pull okay as well. but when he just
> starts to put his foot down it seems to be missing. it sounds JUST like an
> old air-cooled vw bug. and it shakes, etc.
>
> we just replaced the plugs because it was cheap and quick and that may have
> improved things slightly, but the miss is still there. I figure the miata,
> lending itself to the scca as it does, and thinking some of you guys might
> be scca guys, somebody might know that all miatas have this issue, and it's
> the left hand muffler bearing that needs to be replaced. I am the car guy at
> the office, and I'm new so it'd be nice to look good. any ideas?
>
> thanks.
>
> scott
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Miq Millman miq@bigllama.com
Tualatin, OR Big Llama Productions
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