the Opti-Spark design is good. In fact,
high-resolution engine speed sensing leads
to extremely accurate ignition timing, and
was a rare occurrence even on high-dollar
sports cars back in 1992. In practice however,
quite a few things are problematic with
GM's execution of the Opti-Spark distributor.
First and foremost, there are the typical
wear, heat, and moisture problems
associated with a distributor cap and rotor.
Since most Chevrolet V8 engines feature
an easily accessible rear-mounted distributor,
it is not a big deal to change the cap and
rotor every 50,000 miles (or sooner in high
performance applications). Plus, the availability
of standard-style cap and rotor assemblies
makes them extremely cheap. These facts
do NOT hold true for engines with the Opti-Spark
From an accessibility standpoint,
both the water pump and the crank pulley
need to be removed in order to gain access
to a failed Opti-Spark distributor. On Camaros
and Firebirds in particular, this is not
a quick (or fun) job.
From a reliability standpoint, the
environment at the front of the engine is
notoriously harsh for things like heat,
water, and debris (not to mention other
variables like leaky front crank seals and
worn, leaking water pumps!), but the Opti-Spark
distributor is not even sealed on 1992-1994
models! Later versions of the Opti-Spark
incorporate a seal and venting provision,
but are by no means free of problems.
From a cost standpoint, the Opti-Spark
units can retail for well over $400, depending
on model year. Dealers have been heard to
quote over $1000 (parts and labor) to replace
To add insult to injury, the Opti-Spark
distributor uses a "Correct-a-Cap" design
that places the spark plug wire terminals
on the proper side of the engine for easy
spark plug wire routing. To do this, the
terminal traces molded into the distributor
cap must come extremely close to one another,
which leads to premature arc-over
in high-load applications and applications
using constant high-voltage (Capacitive
Discharge) ignitions. Not good.
But not all is defective on the Opti-Spark
distributor. Inherently, the optical sensors
are fairly robust. For most applications,
the sensors are not the cause of most problems.
To prove this fact, Mitsubishi manufactures
the Opti-Spark sensors, and variations on
these same sensors can be found on most
late model Mitsubishi and Nissan applications.
Reliability problems with the optical sensors
on the Nissan and Mitsubishi vehicles are
simply not present in anywhere near the
same quantity as the LT1 and L99 engines.
This would suggest that the main problems
with the Opti-Spark distributor are not
the sensors, but the cap and rotor.