Lincs Cruisers & Classics
Articles
A Spark of Life or the Kiss of Death - The
Opti-Spark
by Red Thunder
GM had an idea, "Let’s evolve the old distributor type
ignition and bring the electrics of our cars into the 29th Century."
‘Great’ we all said because in theory, the Opti-Spark design is good. In
fact, high-resolution engine speed sensing leads to extremely accurate
ignition timing was a rare occurrence even in expensive sports cars back
in 1992. In practice however, quite a few things are problematic with GM's
execution of the Opti-Spark distributor.
This evolutionary ignition component was a bridge between
traditional distributors and the DIS-type, coil-on-plug systems that we
know and love today and should be so much better but unfortunately, LT1
owners have had long-term reliability problems with the Opti-Spark, and
even though it has been around for 17 years now, many enthusiasts are
still in the dark when it comes to identifying, troubleshooting, or
upgrading them.
The Dreaded Opti.
First and foremost, there are the typical wear, heat, and
moisture problems associated with a distributor cap and rotor. Since most
Chevrolet V8 engines featured 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
distributor.
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 a
long and expensive job.
From a reliability standpoint, the environment at the front
of the engine is notoriously harsh for things like heat, water, and
debris, 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.
MSD unit in place.
A friend of mine wanted a ’92 - 94 shape Camaro and when
she was looking for the right car she sensibly asked, "What should I be
looking for on these Chevy LT1’s?" I explained that as long as the engine
was quiet, the body work was clean then the only problem to be aware of
was the Opti-Spark and to try and get a car that had less than 20,000
miles on the Opti unit. She found one that had just had a new unit fitted
and went along to see it. She fell in love with it and bought it there and
then. 400 miles later the car became difficult to start. Opti - troubles
and then it failed as they always do. £800 (quite reasonable) later and a
new unit from the States the car was back on the road.
From a cost standpoint, the Opti-Spark units can retail for
well over $400, depending on model year. Dealers quote over £1500 (parts
and labour) to replace this item!
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 moulded 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 ignitions.
Clearly a bad design.
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.
Two engines here show to bad placing of the unit
The best way of minimising problems is make sure that if
you buy a car with this unit fitted make sure that you know that the car
is fitted with a sealed and VENTED type such as an MSD. If not the answer
is clear, don’t touch it with a stick unless you have a spare unit in the
back of the garage and about 80 hours of spare time. If you have to buy a
unit always look to import the unit as UK prices (even with poor exchange
rates) are a rip off.
The Opti-Spark first appeared on the
1992 Corvette and then progressed to the fourth-generation F-body in 1993.
The same ignition is also found in the full-size B-body cars when they
switched to LT1 power for the 1994 model year. During the Opti-Spark's
reign there were three distinct versions of the distributor, but they all
functioned in the same manner. The differences were found in the drive
mechanism along with the design of the housing and vent system.
The Opti-Spark ignition system breaks tradition in a number
of unique ways beyond its optical triggers as you can see below.
The combination of two systems in one. A high-resolution
engine timing system and a low-energy secondary distribution network.
The ability for the ECM to have total control over the
ignition timing through an angle-based spark advance function along with
the ancillary control of altering the cranking start-up ignition timing
based on the ambient air temperature.
This one had an attempt to seal it but it still
failed.
Robust reductions in spark scatter during instantaneous
transient acceleration in comparison with time-based systems.
The ability to benefit from a more aggressive timing curve
without entering the ‘spark knock’ zone.
A large cap design with a widened rotor tip, allowing for
all of the secondary voltage to be delivered radically without employing a
large rotor tip clearance. This reduction in rotor tip clearance also pays
dividends in decreased radio frequency interference generation.
Individual cylinder timing and knock retard
capabilities.
Accurate drive positioning directly from the front of the
camshaft.
No need for mechanical timing adjustment.
But all this is pointless when the unit can be so
unreliable.
LT1 owners have dealt with the Opti-Spark distributor for
many years now, but there is still much confusion regarding the causes and
symptoms of a failing unit. Tapping into the PCM with a scan tool is a
good way to start, but sometimes no codes will be set. Before diving into
the Opti-Spark, be sure to verify that your grounds are good and the coil
and wires are not the source of the problem, as they are much easier to
change.
Symptoms:
* Car suddenly dies and won't restart
* Starts but immediately dies
* Extended cranking to start
* Rough idle
* Sputtering
* Backfiring
* Trouble reaching higher rpm
* Black smoke from exhaust
* Poor performance with car warmed up
* Weak plug wire spark
* Codes 16, 36, and 42 may be set
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