1995-96 Problem areas

[Richard L.]

I am in the market for a late C4, preferably a '96 or '95, to use as a daily driver. However, the optispark ignition has me a bit concerned as does the VATS system. How prevalent are these issues and how can they be dealt with in a reasonable way--both in terms of expertise and expense? I'm drawn to the C4's for their relative lack of complex computer systems that afflict later series cars and for their simple clean styling as well as the reasonable current pricing ($15K-$20K) that I see advertised for the low mileage examples that I seek.
Any and all recommendations very much appreciated.
Ric

[Mark E.]

Richard,

I am living your dream!

In years past, I owned an '87 convertible and a '90 ZR-1 and fell in love with their design and how they perform. So when I mostly retired five years ago, I began my search for another C4. My criteria: 1991 or newer (styling and body integrity), coupe (convertibles have virtually zero storage for trips and a chassis that twists), 6-speed, virtually perfect condition, less than 20k miles. If you search, you can find threads of mine describing the antics during my two year search, including a Greyhound bus ride from Philly to Buffalo during the pandemic to look at a '94 coupe with ~16k miles (nice, but didn't pull the trigger) and later my trip to Syracuse to look at a '93 anniversary edition with 13k miles. The owner purchased it in 1994 from the local Chevy dealer after it was returned as a GM executive car. Since he never drove it in the rain, the chassis was as clean as the rest of the car. $20,000.

I bought the '93, put new tires on it (it had its original Goodyear GSCs), then drove it home to Dallas. Check out my thread pleading for advice after the fuel pump failed in some small town in northern PA. Besides that incident (which I fixed over 4th of July weekend in the motel parking lot), it was a magical road trip.

Three years later and with 30k miles here's the major service and repair items:
- Changed all fluids, filters, tires and belt. Still running the original hoses.
- Rear Bose amps failed at 18k miles. Easy job; cost was a few hundred $.
- Distributor failed at 22k miles. I replaced it with a Petris vented unit which has been trouble free so far. I did the work myself; if you can turn a wrench it's not difficult but time consuming because the water pump must come out. I replaced the plugs and plug wires while at it. Total cost was a few hundred $ plus my labor.
- ECM failed at 29k miles. Search for a recent post of mine about this. Super easy job; total cost was $650 to repair the infamous solder joints.

No problems with VATS. I've heard it's fairly reliable if you keep the key clean and dry. And if it does fail it's not hard to bypass.

Lessons/advice:

- It's an almost perfect long-distance GT car: comfortable (especially if it has the adjustable suspension and sport seats), good amenities (cold AC, Bose, power everything), handles like a go-cart, powerful (LT1 is a high 13 second car and feels as responsive as my '70 454), great fuel mileage (50% overdrive ==> 30+ mpg highway), good visibility (coupe), lots of space in the back (coupe).

- Recommended diagnostic tools: factory shop manuals, Tech 2 diagnostic computer (get a new Chinese replica, not a 30 year-old used one), injector noid light, fuel pressure gauge.

- Carry a roadside kit for trips that includes copied excerpts from the manual (especially the crank no-start diagnostic tree), the above diagnostic tools, some basic hand tools and a spare fuel pump. Sounds like a lot but all of this fits in a small bag.

- Because of the 92-93 ECM's reputation for sudden failure, I just acquired a used spare and plan to carry that on trips too. Cost was a few hundred $, including having it tested by SIA Electronics.

- Watch the C4 buyer's guide video by C&S Corvettes on YouTube. Lyle does a good job describing the pros and cons of each year. For a driver, he favors 94-95 because they're more refined, more reliable (ECM, vented distributor) and are OBD1 (simpler than the new for 1996 OBD2).

- Buy a super low-mileage car in perfect condition. Market value of these cars is so low it does not pay to get anything less.

- When you acquire that super low-mileage C4 in perfect condition, expect to spend a significant amount getting it up to snuff as described above.

- Make friends with Chris Petris, the owner and founder of Petris Automotive. They are C4 experts and also manufacture the best Opti-Spark replacement on the market. Chris offers FREE phone consultations which helped me a bunch.

- If your ECM does fail, SIA Electronics can probably fix it.

Hope this helps. Keep us post during your search for that perfect car.

[David H.]

I am in the market for a late C4, preferably a '96 or '95, to use as a daily driver. However, the optispark ignition has me a bit concerned as does the VATS system. How prevalent are these issues and how can they be dealt with in a reasonable way--both in terms of expertise and expense? I'm drawn to the C4's for their relative lack of complex computer systems that afflict later series cars and for their simple clean styling as well as the reasonable current pricing ($15K-$20K) that I see advertised for the low mileage examples that I seek.
Any and all recommendations very much appreciated.
Ric

Richard

1996 use OBD II for diagnostic. 1995 was a transition year between OBD I and OBD II - like OBD 1.5. Hence some code readers MAY have some issues with a 1995.

Several iterations of Optispark- by 95-96 most issues sort-of sorted out.

Easy check water pump: With hood open - underside of hood. Look for a horizontal line running side-to-side above where your serpentine belt would be running. Line there would indicate water pump leak with spinning belt tossing coolant in line across hood.

As to VATS. Try VATS search on this forum - I believe Dave Perry has responded to VATS questions here. Also I recall Dave Perry has a Restorer article on VATS. Dave is a knowledgeable source on C4 electronics.

Partial VIN stamp on engine driver side rear of block. Stamping is viewed from above. Likely wiring bundles in you way and likely stamp pad covered with road grime.

Check front and rear fiberglass transverse springs for cracks and abrasive wear. I believe new replacement rear fiberglass springs are still available. New front springs are not available, so you are looking at salvage yards.

Dave

[Richard L.]

Mark and Dave,
Thank you very much for your informative replies. Glad you chimed in because I'd concluded--and had read by uninformed self-styled "experts"--that the '96 was THE year to get (not the 92-93 with the attendant solder ECM issues). After your contributions, however, it sounds like the 1994 is the bees-nees so that'll be my new target. I also appreciate the references to Chris Petris and the folks at SIA, both look to be indispensable for all do-it-yourself C-4 owners like most of us.
Again, many thanks. And, of course, if you know or hear of any C4 meeting the criteria, send me a heads up.
Ric

[Gary C.]

FYI - below 1993 the injectors are not "ethanol ready" and have to be replaced.

Get a ZR1 and you won't have to worry about the Optispark ignition.

Gary
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[Mark E.]

FYI - below 1993 the injectors are not "ethanol ready" and have to be replaced.

Get a ZR1 and you won't have to worry about the Optispark ignition.

Gary
....

Good point about injectors. Updated ones are relatively inexpensive and easy to replace.

ZR-1 comment made me chuckle. Best part of ZR-1 is the wow factor when the clamshell hood is opened. One of the most beautiful engines and engine compartments GM offered.

I've owned L98, LT1, and ZR-1 cars. L98 is reliable and simple but runs out of breath before 4,500 rpm. Yet a clean '91 with the updated body and interior, and durable powertrain is a good pick for a driver.

Performance difference between LT1 and ZR-1 is seat of the pants about the same. But the sound of the ZR-1 intake WOT is intoxicating.

[Thomas N.]

Keep in mind this is a 30+ year old car, so even though the mileage is low on some of these cars you are dealing with years of degradation. I bought a low mileage 96 (most refined) and the first things I did was replace the fuel pump (real easy) and the optispark with a Petris unit. While you are in there do the water pump and thermostat, all the rubber hoses, plugs and wires (this is a PITA job but easier when removing the items to get to the optispark). Also replace the coil and coil module and flush/change the coolant. You can get most of the items (GM parts at that, if you go with a LT1 I can send you part numbers) from Rock Auto at a very reasonable price point. I did video all the steps to replace the opti on an LT1, and will be compiling the video to post on my YouTube channel in the near future.

The C4's are great cars. Hard to get into, but if you do the butt scoot technique it helps (don't pull on the steering wheel to get yourself in)! I personally love the short wheelbase, the clamshell hood, the exposed aluminum suspension components and the list goes on. Looking at the car it definately says Corvette from a design point. Removing the targa top is a pain, but using a smoked roof panel makes the car expansive and I don't really remove the top from the car.

The car I found is a basic model, with the standard seats (which I personally like better than the sport seats and you can see the future of what the seats in the C5 will look like) and the basic heating/cooling system with slides and buttons. I also opted for the automatic transmission which suites my needs very well for driving to work and adds to the GT vibe. Driving it to Hampton Roads last year for the Nationals and stuck in bumper to bumper traffic is a breeze. Plus I don't mind my kids taking it when we go to car shows. The ZF manual transmissions can get expensive to repair and the automatic transmissions are plenty around. If I shotgun the transmission, I can pick up a performance rebuilt one for about a grand and be on my way. There are many configurations and choices out there.

Parts are plentiful and available. Mirrock Corvette is a great resource for clean used parts.

There are many out there to help if you decide to pursue this path! Best wishes!

[Richard L.]

Well, since the upgrades seem to be pretty much the same for all the later C-4s, that broadens the field of choice. The best to me appear to be the years '94 to '96. Thomas' list of chores sound reasonable as insurance against breakdowns and for long term carefree ownership. My usual m.o. when getting a new toy is to go through it and do all the necessary repairs and upgrades and subsequently to just drive the thing, maintain it and leave well enough alone. So, spending at the outset is expected in exchange for peace of mind later on. Don't know what Thomas spent but I'd guess somewhere around $1,500-$2,000 which I'd find reasonable enough--parts only from Rock Auto and labor from yours truly. A great way to learn and bond with a "new" car.
Thank you all again for great tips and advice.
Ric (landeira@colorado.edu)

[Pat M.]

Hi Richard, I have owned a 1996 6-speed LT4 convertible since it was brand new and it has been an absolute joy to have. It is not a daily driver, and has led a pampered life, but it has given me no significant problems at all.

Of the many things I love about it is when putt-putting around town it's as mild and well-behaved as any other everyday car. But when you put the pedal down - hold on!

I think C4s, especially late C4s, are very underrated. Good luck and enjoy.

[Keith B.]

I daily drove a 94 LTI from 2006-2017. your biggest problem will be availability of reliable electronic parts. opti is a major one to think about. the 95-96 are better because they are vented. For me replacing the same part many times got old real quick

[Mark E.]

I daily drove a 94 LTI from 2006-2017. your biggest problem will be availability of reliable electronic parts. opti is a major one to think about. the 95-96 are better because they are vented. For me replacing the same part many times got old real quick

It's a good idea to retrofit a vented distributor when replacing a non-vented one. Easy to do.

[Gary C.]

Richard,

FYI - late C4 engines run hotter than you're probably used to. They were designed to run at 232 degrees to pass emissions.

On my '92 ZR1 the 1st radiator fan came on at 225 degrees. The secondary fan came on at 235 degrees unless the air conditioning is running. I wasn't used to a Corvette with engine operating temp at 210~215 degrees. Installed a new Chip and both fans come on at 205 degrees. To improve Texas summer time engine cooling while driving in traffic, the radiator was upgraded to a DeWitt's 2 row unit.

On the ZR1 the coolant actually routes through the plenum. The engineers did this to keep the intake air from freezing up in the winter time. Added a bypass tube which hopefully reduces coolant temperature by not being routed through the plenum.

On 1992~95 the LT1 engines utilize a reverse flow cooling system which is explained in this video https://www.youtube.com/watch?app=desktop&v=IeU1wojC-VQ

Another major difference for consideration is that after 1992 the radio unit was moved from under the dash to behind the passenger seat, which makes it very easy to pull for repair.

A lot of the late C4 radio units and speakers often need to have the capacitors replaced. The C4 radio head (in the dash) also has a high rate of CD-ROM failure.

Good luck with your purchase.

Gary
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[Richard L.]

Gary, not that I don't believe you, I do, but that the normal operating temperature for a late C-4 ('94-'96?) is 232 degrees seems like a recipe for disaster given how little margin there is left for occasional overheating conditions (~250 degrees?)--and we all know that it can happen. Warped heads, seized pistons, cooked hoses and wires under the hood, overflowing radiators and so on. Even Mobil 1, whatever viscosity is prescribed by Chevrolet, would have to be changed at very short intervals, certainly no more than every 4,000 miles. Can that temperature be sustained long term, after all as Thomas Nowak already pointed out, these cars are over 30 years old? Reliability depends on durability I believe, so am I being foolish in thinking that a C-4 can still be reliable after say 40,000 miles and three decades of use? I'd like to know before spending $15K-$20K on a toy that may not bring me back home one day.
Ric

[Gary C.]

Richard,

The hi engine temps were a shock to this ole 1957 283 180 degree engine temp with a max of 212 temp guy.

Well documented fact that GM engineers designed C4 engine temp to be 232 degrees to pass EPA specs.

From what I've read, the engine temps to activate the fans are the same for LT1 and LT5 engines.

My '92 ZR1 was an engineering car. When I bought the ZR1 it had a one off air cleaner on it, which had a big scoop. That big scoop blocked air flow at city traffic speeds. Last year on the Convention Road Tour in traffic the temp gauge reached 250 degrees several times. The car never puked. When we reached Ashville, I stopped at a Harbor Freight and bought a sheet rock hand saw. I cut the scoop off of that one off air cleaner. My friend Rob Musquetier from the Netherlands was with me and he couldn't believe I purposely ruined a one off air cleaner. After removing the scoop, temp didn't get over 235 in stop and go traffic.
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When I got home from the Convention, I ordered a DeWitts 2 row radiator. Hard to believe that GM used the same single row 3/4 inch radiator core for all engines.

Forgot to mention there was a lot of crud when the original radiator was removed. One was a full page from a 2000 porno magazine. 😊

My '92 ZR1 now runs 185~190 at speed and goes up to 210ish with a/c on in 95 degree temps in traffic.

Hopefully, the LT1 guys will share their engine temperature info. I have faith in my '92 to be dependable.

Next week am taking off on the Convention Texas Road Tour and will drive 3,000 miles in my '92 ZR1 over a 3 week plus timeframe.

Am not trying to scare you away from purchasing a C4. Just sharing my experiences. Good luck with your pursuit.

Gary
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[Mark E.]

Following up to Gary's post-

On hot days with the AC off and over 35mph my '93 LT1 runs 190-210 degrees. Below 35mph and AC off temperature will rise until the first fan comes on at around 225 degrees. Temps then drop until the fan automatically switches off at about 210. This happens because there's no air flow through the radiator while fans are off.

But in practice on hot days the AC is on for my comfort, fans are on and the temperature ranges between 180 (thermostat setting for this car) to about 200. So with AC (and consequently fans) on, the cooling system can more than handle any heat load I've encountered.

This car and my previous '90 ZR-1 are the only cars I've driven that run cooler with the AC on because the way the fans are programmed.

My practice- when temperature approaches 210 (which only happens with AC off and running below 35 mph for several minutes) I turn on the AC which kicks on the fans and returns temperatures below 200.

Richard,

Regarding your reservations of reliability/durability-

These cars are mechanically very robust (it's a Chevy small block...) but like virtually every car they have a couple of trouble areas (water sensitive distributor is below the water pump and failure prone ECM solder joints). If those are a concern for a daily, you can always get a Honda crossover.