What year did the optispark begin?

 

To the regret of many LT1 owners 1992 for the first generation, revised with better venting in 1995.

 

What exactly is an opti spark? Was there a recall? Is it a big fix? Can A shadetree fix it...special tools. Not on an LT4? Anyone aware of links that explain this mystery to me. I have an LT4 and LT1.

Grizz

 

ual, you need to get the Factory Service Manuals from Helm Inc., the two volume set (at least). It'll ans. all your questions. And just to summarize, you can work on it but it's not easy. The LT1 and 4s have it.

 

Here's a re-run of a post I made in a thread about this some time ago:

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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 (triggering), 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 720 holes near the outer edge of the triggerwheel. This high-resolution sensor feeds camshaft velocity and acceleration data to the ECM. The other sensor (low-resolution) reads a series of eight holes nearer to the center of the triggerwheel, and it feeds camshaft position data to the ECM. 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 this camshaft data 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, knock sensors, 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. None of this was possible with the existing technology of distributors (including HEI) when the Optispark was being engineered.

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 located 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 unit, made by DynoTech Engineering, 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 last year, 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.

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A shade tree mechanic can do an Opti swap. No special tools are required, but a good set of general mechanic's tools and good mechanical skills are a necessity.

Be well,

SJW

 

SJW - Excellent Summary - I hope that's in the FAQ

 

Damn well said! Good on ya!

 

First let me apologize to alyle for hijacking his post. Second, what a great response. You guys are too good. You do make my wife happy though...I am an airline guy always on the road. She says she will never have to worry about the other woman because I am always on the corvette forum.

Cheers, Grizz

 

And here are some pics from the NCM.
[IMG]47b6db06b3127cce89f4c0fbce1100000016108A bMmzZk4Zti[/IMG]
[IMG]47b6db06b3127cce89f4c0e04f3a00000016108A bMmzZk4Zti[/IMG]
pics didn't work - let me try again.

 

Just in case it isn't apparent the optispark is the mustard colored object on the front ot the engine.

This link gives a great look inside:

http://www.charm.net/~mchaney/optisprk/optisprk.htm

You'll need an E4 Torx female socket to remove the four screws that hold the two halves together and a T9 Torx driver to remove the two screws that secure the rotor.

 

This probably goes without saying, but if you end up having to do your Opti, replace the water pump and plug wires while you have it apart.

 

Actually, it always needs repeating! And unless your plugs are new, may as well replace them, too, if they've got more than 60K miles on them.

 

And the coolant hoses, serpentine belt, and spark plugs, unless they are fresh...

Be well,

SJW

 

I just spotted a couple of errors in my first reply in this thread:

1. I said the Opti is coupled to the camshaft via a gearset. It's not. It's coupled directly to the front of the cam. There are no gears involved. The gearset drives the water pump. This is what happens when I type too fast...

2. I said that the high-res sensor reads a series of 360 holes on the triggerwheel. I'm pretty sure the actual number is 720.

Sorry for the errors. I've edited the original post.

And thanks for the kind words, BigGrizzly and Paul.

Be well,

SJW