VIDEO: Flashback to 1994; an Extended Look into ABITS/OptiSpark

(Despite the age of the information and the dated hairstyles of those involved, we feel that the video provided does offer those new or unfamiliar with ABITS/OptiSpark systems an insightful look at how they operate, how to replace them and why they fail. We feel that even those immensely experienced with these units could learn a thing or two from this film if you haven’t seen it already. We will cover these more extensively on a project vehicle in the near future. -Ed.)

When GM wanted to take a fresh approach at an old idea, they went away from the famed small block and introduced the LT1 – not to be confused with the 1970-72 small-block Chevy of the same engine code or today’s LT1. Though it measured in at the previous generations same 350 ci., this engine featured several revolutionary advances in technology over the original; including, a reverse cooling system and all new distributor, commonly known as the OptiSpark.

So what is an optispark? The OptiSpark was The General’s update of the HEI ignition system, and is known as an ABITS system which stands for Angle Based Ignition Timing. OptiSpark distributors use an encapsulated plastic distributor cap to protect the conductive ink that transfers the high-voltage to the spark plug wires from the rotor and uses an optical sensor which reads a disk that is driven by the camshaft.


For the sake of the video, the filmmakers decided to throw in the Z28 to remind the viewer the performance roots of which the Roadmaster’s LT1 sprouted from. Apart from the “first base/homeplate” induction tubing found in all B-bodies of ’94-’96 accessing the OptiSpark isn’t any different than in an F-body.

The Opti also uses a rotor to send voltage to the leads which send voltage through the wires and firing the spark plugs. Utilized in the GEN-II LT1 V8, they were found in the ’92-96 Corvette, ’93-97 Camaro/Firebird, and the ’94-96 GM B-bodies which included the Impala SS, Caprice, Roadmaster, and Fleetwood.

The heart of the OptiSpark was the photo diode pairs found in the optical sensor that read the sensor disk which was driven by the camshaft. Instead of the distributor being found on the top on the engine the OptiSpark is located below the water pump, directly driven by the camshaft.

Many LT1 enthusiasts can tell you horror stories of OptiSparks failing and causing all kinds of drivability issues. So let’s look at some common ways the OptiSpark could give you issues. A by-product of high voltage ignition system is ozone which is heavier than air. Ozone combined with nitrogen and oxygen causes nitric acid which corrodes the terminal of the distributor which leads to misfires and crossfires.

To help avoid this issue GM used an air ventilation system – fresh filtered air was drawn in from an air inlet tube. The air inlet tube connects to the air tube pass the mass airflow sensor to the distributor. The fresh air is drawn in by a vacuumed line that connects from the distributor to the intake manifold. There is a filter in the fresh air line and a check valve in the vacuum line. If the lines become pinched or the filter and check valve become clogged it could cause a misfire.


This pesky little devil has caused thousands of enthusiasts to sell their cars, lose their temper, hit things with hammers, curse, drink and ultimately, switch to LS power. But just a few simple tips in this film can help make them reconsider and takes things one step at a time. (-Ed.)

Things you want to check when inspecting the system is looking for pinched or damaged hoses, plugged orifice and filter. Also an improper distributor cap seal, optical sensor failure or the ecm can cause issues with the optispark. Also the location of the optispark created problems for the units. Since they were installed behind the water pump, whenever the water pump had issues or leaked the moisture would wreak havoc on the distributor.

GM created a new system, though it had its problems let to the coil on cylinder desing that we all embrace. Some people have gone to an LS coil pack system in order to, do away with the problem plague optispark. But that is a whole different article.

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