The LT1 Opti-Spark Distributor

Time: 2 hours

Tools: A Visa card with a large credit line.

Talent: (4)

Applicable Years: 1992 to 1996

Tab: $500 to $1,000

Tip: Don’t ever let any water get in the area of the Opti-Spark if you detail your engine compartment.

Complementary Work: This would be a good time to install new spark plug wires. Spark plug wires on the LT1 are a major effort. It usually takes around four hours. I would install the new Opti-Spark and when you’re sure the engine runs properly get started on the spark plugs and the spark plug wires.

This new Opti-Spark distributor was supposed to be the greatest thing since GM did away with ignition points. Instead there was an internal mistake and the Opti-Spark caused Corvette owners a tremendous amount of aggravation.

One of the goals was to control spark scatter during transient maneuvers, such as acceleration. GM also wanted to eliminate the large timing errors that happen during starting. This was a traditional problem with magnetic reluctance timing sensors.

The Opti-Spark is a distributor with a two track optical position sensor, a keyed drive shaft, an ECM, a single ignition coil and driver and conventional secondary wires and park plugs. Contrary to what many people believe, most spark errors actually occur at low speeds, especially starting, not at high rpm.  Spark errors also occur during transient movements such as acceleration, deceleration and transmission shifts.

A key element in this Opti-Spark system was the increased overall diameter of the distributor which allowed for greater separation between the secondary terminals within the cap. This reduced cap and rotor wear by reducing the ozone formed when the spark is jumping large rotor-to-cap gaps.

The Problem

For all of its innovations, one major problem occurred in the transition to actual production. The casing of the Opti-Spark, which was mounted to the front of the engine, just behind the water pump, was designed with a small hole at the base. This would allow any condensation formed within the distributor to drain out. The design engineering team was very precise about the size of this hole.

After the design was completed the unit was passed on to what is called validation engineering. This group changed the size of the hole without communicating this change to anyone else. The validation team felt the hole was simply too large and would allow water to enter into the distributor. The problem was this new drain hole was simply too small to allow condensation to flow out of the distributor.

Then to make matters just a little worse the validation team changed the composition of the internal components, making them less corrosion resistant. That was all that was needed to make this one of the most failure prone components in Corvette history. Eventually a recall campaign led to all (or most) of the units being replaced.

Today there are several units on the market that incorporate some design changes that make the unit very reliable. This is important since there are no alternatives on the market for the Opti-Spark. It’s not as if you can simply install a different type of distributor.

Petris Enterprises is the only firm that sells the Opti-Spark with all the upgrades. They actually use a flow through ventilation system that circulates air through the distributor cap. I’ve never heard of anyone having a problem with their units.

  • Petris Enterprises’ Optispark unit is equipped with a Mitsubishi-Grade optical sensor module. Our optical sensor is built using components that are equal to or higher quality than the original equipment optical sensor found in factory-supplied distributors.
  • Our Optispark distributor cap has a ventilation port cast into it with high quality brass terminals and high voltage distribution straps.
  • The brass tipped rotor of each unit is secured with Loctite, assembled, and then tested for leakage. The final touch is the installation of a vacuum ventilation hose assembly with the correct check and restrictor valves to prevent distributor cap damage.
  • The Petris Enterprises Optispark kit includes all the pieces and attachments necessary to make the conversion, including manifold fittings, the vacuum hose assembly, and installation instructions. You can rest assured that you will not need to make trips back and forth to the auto parts store to buy another little piece to finish the project.

Just remember to cover the hole when you detail your engine. You have to be very careful when you do any engine detailing with the LT1. A lot of folks have gotten a little carried away cleaning their engine compartments and killed the Opti-Spark in the process. That’s a very expensive mistake.

Before you do any detailing you should take a towel or shop rag and cover the hole in the Opti-Spark casing. I use a shop rag and then duct tape it so no moisture can possibly destroy the unit. You simply can’t take chances.

IMG001IMG001: These dreaded holes create the infamous Opti-Spark problem. Once you kill the unit be prepared to spend some very serious money. I would search out one of the upgraded units – don’t even consider another original equipment part.

IMG002IMG002: This is the Opti-Spark distributor cap. You can easily see how far the terminals are from each other. This greatly improved the low speed performance of the new LT1 engine. At least until the whole distributor failed.

IMG003IMG003: This assembly hides directly behind your water pump and almost directly under the thermostat housing. It’s a shame that the various groups within GM didn’t have a chance to talk to each other and resolve the whole Opti-Spark issue. The LT1 is a great engine – with one huge problem — a problem that could cost you over a thousand dollars.

66.tif: This cutaway LT1 picture from GM shows exactly what is going on with the infamous distributor. While you look at the distributor also look at the spark plug wire routing for the LT1. If you have to replace your spark plug wires you can expect to pay for about four hours of labor. That sort of bill makes me happy that I have an L98 engine.

This is an adaptation from Richard Newton’s most recent book 101 Projects for Your Corvette 1984 – 1996. He has also written two other best selling Corvette One deals with the 1968 to 1982 Corvettes, How to Restore and Modify Your Corvette 1968-82 , while another deals with the Sting Rays from 1963 to 1967, Corvette Restoration Guide 1963-1967 All  of these books are available from Corvette Central.

8 thoughts to “The LT1 Opti-Spark Distributor”

  1. I am on my 3rd optispark in my 1994 Corvette and this time will sell the car when its fixed again. My mechanic always insisted on genuine GM OEM one so it is warranted. But still have to pay the labor for him to replace it. The car dies while driving down the highway. He said ECM caused the new optispark to fail. Then just put it back on the road for summer and it died again at a gas station. Turns over but wont start. You could tell it was the optispark since it tried to kick but you could tell the timing was off. The mechanic and the gas station verified it was the optispark. I had it towed back to my original mechanic to repair since the thing was still under warranty. Buy a C5 vette with the LS1 engine.

  2. I replaced the opti spark and now the engine RPMs are hunting at low throttle demand. I checked all the vacuum lines and found no leaks. I also changed IAC, alternator, battery and water pump. Is there a re-learn procedure or something that I am missing?

  3. I have a 1992 corvette convertible LT1 which fires up then dies out then won’t start again. I’m thinking it’s the body strap (braided ground). I heard if these are rusty (and mine is very rusty down there) then you’ll need to wire wheel the area down and pick up a new strap.

  4. I washed the engine and killed the optispark. Replaced the opti and it died in 40 miles for no reason. I am going to the coil pack system. I wish that I still had my 89 vette with the L98 engine, easy to work on. If the cancer I have will let me I will fix it this next summer 2016. Is there any Vette person out there that lives in the Boone NC area. Please contact me at … I thank you all.

  5. Thanks for the help. This article was very very helpful and even tho I’m disappointed in myself for ruining my distributor. Im happy I can start to fix it. A shame such a big problem came from keeping the engine of my 93 Vette clean. Great help tho and thanks again

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