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

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Jul 13, 2020
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268
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San Diego County
The key part is Mitsubishi optical sensor used on oem cars. Look for the 3 triangles logo inside. All others are junk. As a LT1 owner and longtime member of the ImpalaSS forum, I have three original used vented optisparks. Clean, tested, low miles.I could sell one.

Many owners have gone hundreds of thousand miles on GM originals. Great misunderstanding and unfounded criticism on this subject. Cap and rotor replacement as mentioned should be done.
 
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Joined
Nov 22, 2004
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9,057
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Texas
The C4 is one of my specialties and I own a 94 Admiral Blue that I bought brand new.

I can do an opti, water pump and plugs & wires in around 3hrs. I will tell you this - I hate Cardone with a passion and refuse to use any of their parts EXCEPT their NEW optis...they are actually very good. Never use the rebuilt one. I've installed probably 10 or 15 of these on C4s, F cars and Impalas. The Accel is not a quality part. You can still get a Delphi which is good if you add the vent kit that the 95+ use. I have used Accel a customer brought in and it lasted 6 mos. I refuse to install any Amazon or Autozone/ORielly unit as well. You can go with an MSD that is a solid unit, the NEW Cardone or a Delphi and be ok. It is hard to find one using the OEM style Mitsu optics so if you find the cap and rotor are corrided - just replace them and keep the stock unit but I doubt the stock unit is on there at 100k.

I think the C4 is underrated but is starting to gain some appreciation. Without the C4 we wouldn't be were we are today. It was a world class car in it's day.
 
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Nov 22, 2004
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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
Do not remove the hood. No reason too and the body fitment steps for a C4 are horrendous. I remember watching the fitters in Bowling Green doing it and it was very methodical. Remember you have the hood, the bumper, the bumper cap and 2 fenders to fit....leave hood on.
 
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Aug 19, 2010
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Only LT-1's had Optispark?
The 1996 Chevrolet Caprice Classic -a fully loaded trailering vehicle- I sold for my neighbor had Optispark.
Having never seen one before, I asked around. The rockslide of loathing and contempt was astounding.
It seems the system wasn't completely horrid.

Since there'd be little doubt that Optispark saved production costs, I wonder who's shrieking killed it.
 
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Joined
Sep 27, 2015
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USA
Why would a problem with the crank sensor also require replacement of the distributor, or vise versa?

There were also a few Japanese designs with 360 degree optical wheels. The reason they went away is better computers that could interpolate between the 10 degree or so pulses of a magnetic crank sensor. The computer would predict the engine angle and fire sparks timed to the degree even though the sensor was not providing one per degree pulses.
 
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Oct 7, 2012
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Staten Island, NY
Why would a problem with the crank sensor also require replacement of the distributor, or vise versa?

There were also a few Japanese designs with 360 degree optical wheels. The reason they went away is better computers that could interpolate between the 10 degree or so pulses of a magnetic crank sensor. The computer would predict the engine angle and fire sparks timed to the degree even though the sensor was not providing one per degree pulses.
If you own a Mid 1990s to Mid 2000s Nissan, you'll know it well
That little optic sensor drives fuel injector pulse/spark timing and when it fails erratically, they become undrivable
Hell hath no fury like a VG series owner on distributor number three or more
I went through at least 2 on my Villager
Good old NS60 🤮
The difference on Nissans at least is you can change the whole distributor in a parking lot with a socket or two in 10 minutes or so, it's not that major of a job
 
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Only LT-1's had Optispark?
The 1996 Chevrolet Caprice Classic -a fully loaded trailering vehicle- I sold for my neighbor had Optispark.
Having never seen one before, I asked around. The rockslide of loathing and contempt was astounding.
It seems the system wasn't completely horrid.

Since there'd be little doubt that Optispark saved production costs, I wonder who's shrieking killed it.
The LT-1 is the engine designation. Later Buick Roadmaster and Caprice had this engine.
The 1996 'Vette had a LT-4 variant of the LT-1 on MT equipped cars.
One of the BETTER small block chevy engines ever made
 
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Jul 24, 2020
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The later vented opti's were much less horrible than the early non-vented ones, I'll give it that much praise. I didn't have my C4 long enough to have to mess with it, lucky me. Everything else on the car tried to kill itself in 40k miles... brakes, wheel bearings, EGR, U-joints, tie rods, fuel pumps, leaky sunroof, a 4L60E that loved to give a horrific metallic clunk-crunch on the 2-3 shift....gorgeous car, lovely sounds and 25+ mpg out of a 300hp V8, it had many good points. But too many little mechanical things every other day to mess with, just took too much of the joy of owning it. If the opti would have failed I probably would have pushed the pretty little thing off a cliff without an ounce of regret or guilt. Even my dang Fiat hasn't given me 1/1000th of the problems that young C4 did.
 
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Jun 25, 2022
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Back when I had a 93 TransAm, I had to replace the OEM non vented opti every year I owned it for 3 years till I finally got rid of it. In retrospect I think it was due to a leaking intake gasket. If I had to replace an Opti now that OEM is discontinued, I would try the petri opti. They have the Mitsubishi grade optical sensors and a quick google search seems to indicate good results so far. https://petrisenterprises.com/collections/frontpage/products/1992-1994-optispark-distributor
 
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Dec 19, 2013
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Fort Worth, Texas
I've converted a couple LT1's to 24X crank sensor & 1X cam sensor allowing the use of a P01 LSx PCM & 8 individual ignition coils, The conversion parts are available from EFI Connection.

Both were high dollar Forged bottom end Strokers that the owners had too much money in the engines to switch directions & do a LSx swap. It wasn't just because Opti issues either....LT1 PCM's are very limited.
 
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2,378
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There's a very reputable guy on eBay that rebuilds original optispark units. He will send you a link to a video demonstrating the proper operation of your rebuilt unit, and ship it back to you. Nothing better than the original. Email Brad at [email protected], he does great work.
Also Sac City Vettes has a solid replacement unit: https://www.saccitycorvette.com/AIPOptiSpark.html
C4s are good cars if you can find one that is in good (and mostly original) condition. Unfortunately the C4 is in between the classics and the modern Vettes and get poo-pood a lot. My C4s were both awesome cars, no problems of any kind... love the LT1 M6 combination, so fun to drive.
 

LDM

Joined
Nov 8, 2018
Messages
255
Location
Illinois
I've had my 94 Z28 for over 20 years now, I've replaced the Opti once the entire time. Most of the horror stories are over-exaggerated in the extreme. The biggest issue was the location as it is right under the water pump and anytime the water pump would fail or start to fail, it would leak coolant directly onto the Opti, killing it in the process. Yes, they were not a perfect design but the biggest issue was most people have no idea how to diagnose issues with them and refused to learn. Today the biggest issue is find one that isn't total garbage reman units, which is getting harder since GM stopped making them some years ago.

But if you still have an LT1, there are new options available to eliminate the Opti like the Torqhead, which will also let you update to the 411 PCM and use that for tuning. Lot easier to find a tuner that can handle the LS1 411 PCM than the old 94-95 OBD1 and 96-97 OBD2 LT1 PCMs these days. My plan with my 94 is to swap to a TorqHead when I do my 383 build. No more slow LT1 PCM that limits RPMs and other factors while tuning.
 

LDM

Joined
Nov 8, 2018
Messages
255
Location
Illinois
Only LT-1's had Optispark?
The 1996 Chevrolet Caprice Classic -a fully loaded trailering vehicle- I sold for my neighbor had Optispark.
Having never seen one before, I asked around. The rockslide of loathing and contempt was astounding.
It seems the system wasn't completely horrid.

Since there'd be little doubt that Optispark saved production costs, I wonder who's shrieking killed it.
Yes, only LT1/4/99 engines from 92-97 had the Optispark. Your 96 Caprice Classic either had the L99 (which was a 4.3L small version V8 of the LT1 for fuel economy purposes) or the LT1. Most likely the LT1 if it had the trailing package. The LT4 was only ever offered in the 96 Grand Sport Corvette and the 97 Camaro SS/Trans Am and in very limited numbers.
 
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