i can't believe all the opti-problems i've read about, i have a 1995 and now i'm paranoid as all get out now. is this problem indicative to corvettes or is this just a small sampling of vette owners? why did gm switch to this system? any educational info would be welcome. thanks Frank

 

Thank god it was a short lived system. I replaced the opti on my 93 when I had it. The problem was moisture getting into it. Some C4's never have any problems. Some have many. A leaking water pump gets to a lot of them. They make a newer vented opti to help keep the moisture out. The engineers were not thinking about the person that has to replace it when it goes bad.

 

I just replaced mine today with a cheap $79 unit from fleabay. The reason it went bad in the first place is because. One time I opened the brass bleed screw on the thermostat housing. I did this because I was changing out the coolant. This resulted in a tiny trail of coolant leaking onto the optispark. And not knowing any better I started the car right away and it backfired like crazy. Sure enough however, about 6 months later my car started really hard as well as pinged and knocked like a ****.

 

The optispark was used on all full size cars for 5 or so years.The 1995,96 and 97 GM applications were sealed and the engine vacuum pulled intake air thru the sealed unit thru a check valve and air filter. These are the 'Vented' version in 95 and 96 Corvettes. They are not a problem. I wash my Corvette engine (1995) regularly, sometimes even pressure wash it and I have never had a problem. I recently replaced my optispark not because it failed but because the WP had failed and I'm at 96 K miles. The nonsealed units can be retro-fitted to the earlier models, check forum threads for process.

 

I know of many 95' / 96' s going well over 150K Miles w/o a problem.

 

I sure hope you modified it with the upgrade for the vented 1995-1996 type. I have a 1992 with 283,000 miles on the original motor and have had three Gm/Delco type on it so far. The first one was non-vented, original and got anti freeze on it when a hose broke at 125,000 miles. I have vented the last two. I changed it two years ago not because it quit, but because I was changing the front cover gasket and seals and figured why put the old one back on.

 

Here's a quick tutorial for you. I posted this here some years ago, and dug it out of my files to answer some of your questions. (Note: I don't know if the Delteq or DynaSpark are still being sold).

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The Optispark is a distributor, but is rather different from any other distributor. It is mounted to the front of the timing cover, and it is mechanically coupled to the front end of the camshaft.

The Optispark is essentially a two-part device. It contains a low-voltage optical section (camshaft sensors), and a high-voltage section (distribution of spark) that uses a cap & rotor.

The optical section uses two optical sensors and a triggerwheel to determine, with great accuracy, the position, velocity, and acceleration of the camshaft. One sensor (the high-resolution sensor) reads a series of holes near the outer edge of the triggerwheel. This high-resolution sensor feeds electrical pulses to the ECM, which the ECM then uses to calculate camshaft velocity and acceleration. The other sensor (low-resolution) reads a series of eight holes nearer to the center of the triggerwheel, and it feeds electrical pulses to the ECM, which the ECM then uses to calculate camshaft position. The engine will run (although not optimally) if the high-resolution signal is absent, but it will not run if the low-resolution signal vanishes.

The ECM uses these timing pulses from the optical section of the Optispark, in combination with data from numerous other on-board sensors (Vehicle Speed Sensor, Mass Air Flow Sensor, Engine Coolant Temperature Sensor, Knock Sensor, Intake Air Temperature Sensor, Manifold Absolute Pressure Sensor, Throttle Position Sensor, etc) to exercise very tight control over spark timing. In fact, the ECM can even retard the spark on only the offending cylinder, in the event that one of the knock sensors triggers.

The high-voltage, distributor section of the Optispark functions the same as the cap and rotor of any conventional distributor, but the cap is rather different in its design. Because the plug wire towers are not spaced equidistant around the cap, and because the towers are not arranged in the same sequence as the engine’s firing order, conductive ink is used to make the connections from the contacts to the towers.

The Optispark was, conceptually, a brilliant design, but it suffered from two major flaws:

1.There were durability issues, a great many of which were associated with moisture build-up inside of the Opti. This moisture build-up could result from condensation, or from invasion of liquid from outside if the Opti got douched by coolant from a leaking water pump, hose, etc, or if the engine was cleaned with a water hose.

2.The Opti was mounted to the timing cover, behind and beneath the water pump. This placement left the unit vulnerable to coolant leaks (see 1 above), and also placed the unit where accessibility was a major issue in the event that a problem developed with the Opti.

The Optispark works extremely well, so long as everything’s in order. Problems only arise when something goes wrong with the unit, and it can become a major headache mostly because of the relative inaccessibility of the unit because of its placement on the front of the engine. Digging down to gain access to the Opti requires removal of the water pump, etc.

The Opti was used on the Corvette LT1 engines from ’92 – ’96, and on the LT4 engine (which only was used on manual transmission Corvettes in ’96). GM revised the design of the Opti mid-way through its life. The first-generation Opti was used on ’92 – ’94 Corvettes, and the revised, second-generation Opti was used on ’95 and ’96 Corvettes. The first-gen Opti was passively vented with three weep holes to allow moisture to drain out of the unit. This proved inadequate, and the revised, second-gen Opti was actively vented using intake manifold vacuum to draw filtered air through the Opti’s housing. The second-gen Opti was a major improvement over the first-gen units.

There are several aftermarket products available which attempt to address the Opti problems:

1.The DynaSpark is a direct, bolt-on replacement for the entire Optispark unit. It is a very well-engineered and well-manufactured item, and is also actively vented. It sells for approximately $600.

2. MSD is now also selling a direct, bolt-on replacement for the Opti. This unit is new to the market, so there isn't a lot of field history available to suggest how well it holds up.

3.The Delteq system is a DIS conversion package that eliminates the high-voltage section of the Opti. It uses four Cadillac Northstar wastespark coilpacks to deliver spark to the eight spark plugs. This system is carried on a bracket that mounts on the driver’s side valve cover of the LT1/LT4 engine. It requires the use of different-length plug wires, and on some Corvettes also requires either the elimination of the tachometer filter, or the addition of a MSD tach amplifier, in order to preserve the operation of the factory tachometer. It’s important to note that the Delteq system does not eliminate the optical section of the Optispark. The ECM will still require the camshaft data from the Opti to drive the Delteq system. The Delteq also adds some clutter and a non-stock appearance to the engine bay.

4.The LTCC system is similar conceptually to the Delteq, and accomplishes basically the same things, but it uses eight LS1-style coilpacks, rather than the four Northstar wastespark coilpacks that the Delteq uses.

I installed a DynaSpark on my ’94 in August 2004, and I’m very pleased with it. The car runs great, and I no longer have any anxieties about Opti issues.

The issues surrounding the Optispark should be understood by those who own, or are considering purchasing, a car that uses the Opti. So long as they are understood, there’s no reason to be scared away from owning and enjoying these great, LT1 or LT4 Corvettes.

I hope this helps to remove some of the mystery about the OptiSpark.

Live well,

SJW

 

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Vented OPTIS rule

(Used on 94-96 B bodies too)

 

what many people don't realize is that an OPTI is a distributor, with a rotor and rotor cap that have to be replaced periodically. I suspect what many people believe, or are led to believe, is an OPTI failure, is in fact, nothing more than a worn out rotor and rotor cap. the late OPTIs are very reliable and rack up some insanely high mileage numbers.

one hint, even with the late optis, the vacum venting hoses must be maintained...on my 96 the hose to the opti had been cut by the fan belt at some time, and the hose to the intake manifold had deteriorated had rotted and failed from heat and oil.