Early Opti-Spark systems had a tendency to collect moisture that would interfere with the function of the optical sensor and cause the engine to run very poorly. This condition would often induce cross- and misfire similar to a cracked distributor cap on a conventional ignition. Two distinct faults were at work when this occurred. The first was inaccurate primary interrupts from the moisture affecting the optical sensor's ability to clearly define the leading and falling edges of the 360-slot wheel. The second was more rudimentary. Electricity taking the path of least resistance, the high-energy secondary voltage would sooner follow the moisture down into the cap than bridge the spark plug under cylinder pressure. The high voltage would burn through the rotor or the slotted wheel, stopping the engine in its tracks.


To eliminate this problem, later designs incorporated a more efficient venting system that pulled air through the distributor housing from the throttle body. This was supposed to eliminate once and for all the moisture issue.

Other changes were made over the years to the engine-side of the housing and the size and attachment of the drive mechanism. Due to this there are three different timing case covers used on LT1 engines. Abe Bergian, motorsports service manager at Jay Fisher Pontiac-GMC, explained that the 1992 to 1994 versions of the Opti-Spark on both F- and Y-cars had no vent and used the timing case cover with a small distributor drive hole. 1994 B-cars used a new timing case and companion Opti-Spark that had increased venting, a serviceable cap and rotor, and a new-style drive attachment to the camshaft. This style was then switched to the F- and Y-cars for the 1995 model year. With the arrival of OBD-II for 1996, the timing case was again modified to accept a crankshaft sensor for misfire diagnostics but the Opti-Spark was unchanged. The older-style unvented design can be updated to the final version but would require a new-style timing case, Opti-Spark distributor, and changes to the cam drive mechanism. In addition, a longer dowel pin needs to be installed in the camshaft to drive the distributor. The first iteration used a traditional short Chevrolet cam dowel pin.