Lucky me... GM Opti-spark repair on a C4

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Wouldn't you know it... my first day back from Vacation and one of my best/most irritating customers had their '94 C4 convertible towed in. Complaint was "died in flight". I've got good fuel pressure, good compression, no spark. We all know where this is headed... the dreaded Optispark. Last time I repaired one of these had to have been at least a decade ago... even GM can't get the part anymore. I refuse to install a Cardone, so we're going with an Accel which is supposedly brand new. Yea, sure.

The car in question has it's original plugs, wires, and I assume dizzy and water pump. This is a 100k mile C4, to be clear. Assuming my customer approves the work, I'll be replacing everything from the WP to the spark plugs. Part of me hopes the customer bails... he picked this thing up at an estate sale for a song about 6 years ago and barely drives the thing. It's just a Polo Green over Tan convertible, auto trans, about 100k on the dash but it's exceptionally clean. I figure I'll low-ball him to the point I'm borderline offensive... something like $4k as-is. Assuming it does need all the work I mentioned, I'd be looking at 4-5 hours labor and $3-400 in parts, wholesale.

I realize that C4 Vette's are generally scoffed at, however the way I see it there will always be a market for ANY Corvette, especially drop tops (unless one plans on track driving). The car in question has been personally serviced by me since my customer acquired the thing at an estate sale. It's sporting new tires, all new brakes, new rear wheel hubs, along with numerous little odds and ends. 100% stock, also, right down to the radio and air intake.

Anywho, should my customer go forward with the repair I'll be sure to document the process. I've only worked on one Optispark in my career, and I don't remember it being fun.
 

ls1mike

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I have done about 6 Optisarks on different vehicles. Some F-bodies and Corvettes. Get the vented one from Summit. I never minded swapping them out. Not a huge job by any means. To me most timing belts are worse. It is the plugs and wires that suck on an F-body. As I recall the were easier on the Corvette.
 

ZeeOSix

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The whole hood tilts forward in a C4, so the engine is a bit more exposed.

Capture+_2022-06-23-01-45-45-1.jpg
 
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Polo Green is IMHO, the best color on a C4. Too bad it’s not a manual. They are under appreciated cars for sure.
Buddy at work did the optispark on his GF Camaro. Half day job he told me.
curious to see how this works out.
 
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Is that the engine that used the camshaft driven water pump? If it is don't lose that little drive sleeve as most people do then wonder why the thing overheats.

I seem to remember replacing that coil looking thing with all 8 plug wires going to it once.
 

ls1mike

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Wasn't there a conversion kit for these that used N* coils. I guess a lot of trick parts for these are no longer available.
You still need the optical trigger, but as I recall it removes the high voltage from the Opstispark. You use LS coils or N* coils. but it generally eliminates the failures.

The vented opti really helped with the moisture issues. I replaced one at 120,000 and the second was still fine at 210,000. When they sit, like Camaro's, Trans Am and Corvette sometimes will is when most of the problems arise.

Cam driven water pump. Reverse cooling from the traditional SBC. Still the LT1 is a good engine, beside the opti which is just a distributor the only other big issue I can recall having is intake gasket leaks. Typical of a traditional SBC.
 
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Not a terrible job. plus, no puller needed on the harmonic damper.

Better than most T- belt jobs. Remove the clamshell hood of course,

These are good driving vettes. Still had good driver involvement - a bargain.

I am looking for a nice 1996 LT4 engined car
 
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I have done about 6 Optisarks on different vehicles. Some F-bodies and Corvettes. Get the vented one from Summit. I never minded swapping them out. Not a huge job by any means. To me most timing belts are worse. It is the plugs and wires that suck on an F-body. As I recall the were easier on the Corvette.
Plugs and wires on the f bodies suck!
 
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I love C4, had a 96 LT1, 300hp is more than enough. Wish I had room for another car I would love to have one.
 

14Accent

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Well folks, it looks like my customer is going to bail. Against my usual protocol, I spoke with him one on one this afternoon, laying reality out on the line for him.

After a brief look on eBay, auto C4 convertibles are asking in the neighborhood of $10-12k with 100k. I told my customer that he should be able to easily ditch his ride for $3-4k, as a non-runner. Surely, some Corvette lover will pick it up.

The biggest issue comes down to availability. It's generally accepted that nothing but an OEM distributor will provide any sense of reliability. Unfortunately, the OEM reman's were discontinued in 2018, and the ACD "Professional" isn't far behind. We found a dealer in WI that had one on hand, but they wouldn't sell it to my local dealer, nor would they ship it.

I refuse to install a Cardone, WAI, "Napa", or any other unit. Given the limited run for the Opti, there's very little incentive for the aftermarket to produce anything worth it's price. Even GM realized that it was a dead system, hence the lack of OE parts.

Given the fact that the Optispark was only used from 94-96, and only on the LT1, it's always been a bit of a black sheep. I appreciate what GM was trying to accomplish... however I can't help but feel that it was too much, too soon.
 
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