Hi everybody -

I have owned my C4 (first Corvette!) for about 2 weeks now. The 1992 is a completely stock LT1 with side-pipe exhaust - other than that, the car is in factory condition. It only has 37,000 original miles at this point.

Tonight, while accelerating through about 30 mph in 2nd gear (car was already warm) the engine seemed to shut completely off - as if someone pulled the plug electrically - for a split second. The Tachometer bounced like crazy and the car lurched forward as I lost acceleration. Then, before I knew what was going on - the power came back and I was driving along again.

The Service Engine Soon light came on immediately afterwards. I drove home (about 20 miles) with the light on. The car was hesitating in all gears. When I got home, I played with the car in neutral - As I slowly pushed down the gas pedal, the car bogged down around 1800 rpms. To get through that spot, I had to really punch the gas.

When I shut it down - it would not restart (the engine cranked,but wouldn't light-off).

I disconnected the battery for about 20 minutes - then reconnected. The engine starts fine now and the light is off. I notice no hesitation at the moment.

Can anyone help me troubleshoot?
Any good shops near Cherry Hill, New Jersey that might be able to help?

Thanks a lot -
Andy

 

You should have pulled the code before pulling the battery wire.
When it does it again pull the codes, search will give you at least two methods.

Whlie you are waiting for it to happen again ohm your injectors, see the sticky from FIC for the procedure.

Since you threw a code you need to track it down first.

OBTW DO NOT PRESSURE WASH THE ENGINE!!!!!!!!!!!

 

You might be having problems from the opti-spark, better known as the opti (distributor). Sure does some of the symptoms of it. Acts up when hot, tack jumping, bucks and kicks with throttle advance.

I not saying to jump right on it but is an area of consideration. Do all the normal checks before going down that path. Another likely suspect for that condition is the ICM (ignition control module). Its basically a solid state amplifier that amplifiers the pulse from the ECM and than drives the coil.

 

Thanks for all the replies - I drove the car all morning today - lots of starts and stops - lots of engines starts between errands. Oil temp got up to 195 (seems to be where it likes to hang out) so it was warmed up.

Anyways - At this moment, there's nothing wrong. I checked the codes (thanks for the advice on that one!) and it's flashing a continuous 12 code, so it looks good there.

I'm going to keep driving it like normal, and if it happens again, I'll pull the code and report back.

Thanks -

Andy

PS - Any good shops that people like in Southern NJ? Philadelphia? What about Classic Chevrolet with the Corvette Corner - anyone ever been there?

 

Okay -

The symptoms came back tonight. Trouble Code 36 is my only code. My manual says:

MAF (Mass Air Flow Sensor) burn off circuit problem

OR Direct Ignition System fault - loss of 24x signal or extra or missing pulses in electronic spark timing signal

OR Ignition system fault - loss of High Resolution Pulse Signal.

So - is it a good assumption that I've got the Opti Spark going bad?
What do you think?

Thanks - Andy

 

Probably, but check the wiring harness first.


I hope you have deep pockets if you plan to have other people do this sort of work for you...

 

Definitely don't have deep pockets - In the Air Force and working on the government salary! Any idea what it would cost to remove the bad opti and replace it with the newer system that doesn't fail

Also - what about the possibility that I could have a bad Mass Air Flow Sensor? I'm thinking about this because the problem only happens rarely - and when it does, a computer reset fixes it immediately and keeps it gone for a while (this time I drove about 100 miles before it happened again).

Thanks -
Andy
(BTW - I grew up in Pittsburgh - South Hills!)

 

Sounds like the opti. But like previous posters said, check everything before starting that job.

My advice is learn to turn a wrench. The opti is a $1500+ job if a mechanic does it. The most reputable mechanic in my home town wanted $1,900 to replace the opti, waterpump, plugs, and wires. I did the opti and water pump for under $600.

Normally, what causes the opti to fail is the water pump bearings starting to leak. With a 17 year old car, mileage means nothing when it comes to how long things like water pumps last. There is a weep hole on the bottom of the water pump. You should be able to feel it with your finger. If it is wet, that means your water pump is on it's way out and the opti is probably toast as it is located right below the water pump. Opti's are VERY sensitive to moisture. The optispark is fine itself, GM just put it in a horrible location hear the bottom front of the block where it is constantly assaulted by heat, moisture, road debris, etc.

That means you would have to replace the water pump and the opti. And while you're at, it you might as well replace the spark plug wires as well.

The opti job isn't bad if you have a good complete set of wrenches, ratchets, and sockets. I thought the only hard part was getting the harmonic balancer off. Mine was frozen onto the hub. For some people it came off with no problem.

Good luck!!

 

Another thought - the problem is inconsistent - it only happens every once in a while. It never starts in the middle of a long drive - it always starts just after a start-up while the car is warm. Is that consistent with an Optispark fail?

 

Although initially the symptoms did at first sound like an opti, the later posts have gotten me thinking in a broader direction. Most opti problems happen when engine heats up and on a pretty regular basis. That has been my personal experience and what I have read.

Driving a 100 miles with no problem makes me suspicious. Also re-setting the computers would not affect the opti. Its also spitting out these codes leads me to believe that its very possible the ECM might be the root of the problem. It is a 92 and known for having bad ECMs

I think some attention should be focused on the ECM. Put a lump of ice on it, rap it or pull the fuse for it when problem occurs. Try to see if some direct stimulus might show something up.


Opti usually will not shut it down but will bog, kick back and cough. Tach bouncing and service engine light all can point to ECM. I missed these symptom and was to quick on the opti. Look at these symptoms, they are not classic opti, they are ECM.

 

I dont knwo how much a MAF sensor is, but I bet replacing it and the ECU will cost you less than diagnostics at a "good" shop. I highly doubt it is an opti causing an intermittant problem, but it could be that it is getting ready to go. Its probably either a MAF or the ECU. I bet you could get a MAF for cheap enough, and personally I would try that first. I see them all over ebay from $35-100. Autozone has an ECU for like $250.

 

I found no good shops in th area.
A couple of years back when I was doing my re-build, the mechanics at Classic Chervolet couldn't even talk to me about some coloring I found on my 92's cam when I brought it in to ask a question or two.
A few years before that, I had problems with my ASR. They said they fixed it after having it for a long time.
What I later found out is that they disabled it.
Good luck with your search!

 

OK, its a 92 - NO MAF!!!!!! only MAP!

Sorry to be a bearer of bad news its the OPTI.
Save your pennies and get a water pump. vented opti (MSD is probably the best bet here), New plug wires, new waterpump seal, an old dry erase marker, coolant (green), and distilled water, red permatex, anitsieze, dielectric grease - should be $600 - $800 for all these parts
Go to the on base hobby shop (I think thats what it is called) and make sure they have metric and SAE deep sockets, breaker bar, hammer, etc. to loan.

The opti is fairly easy to replace when you get everything around it off.
Drain the coolant, you may want to pull the knock sensors - I just put a bucket under the front of the engine to catch the fluid when I removed the water pump.
Remove the rubber air bridge between the air filter housing and the throttle body.
Remove the water pump - IIRC its 3 bolts on each side
Remove the old gasket
Mark the balancer and remove the 3 bolts holding it on to the snout.
Lucky - it will just drop off
Normal - Long 2x4 or old breaker bar from underneath, wack it a couple of times, use the center bolt to rotate the engine 90 deg, wack it again, repeat until it falls off. Mine took like 3 full revolutions of the engine before it came off. A helper is really helpful so it doesn't take all day.
Pull the old plug wires off the Opti and remove the three bolts holding it on.
CLEAN everything you can see including where the waterpump gaskets go.
You will most likely need to replace the waterpump seal in the timing cover - use the dry erase marker to hold the new seal rigid when pushing it on.
look at your new opti - you will see the gap between two teeth is filled in. If you look where that gear meshes inside the timing cover there is a missing tooth. Align the filled in area with the gap - the opti should "pop" on. The bolts only hold it in place, do not use them to draw the opti on to the drive gear.
Thread the new spark plug wires and install them, you need to have everything hooked up!
Start the car and let it run a few seconds. This verifies all the connections are good and you hooked everything up right.
Forgot - reinstall the balancer using a lite coating of antisieze.
Use some permatex red, a real light covering on the waterpump gaskets to hold them in place on the engine. Make sure you reinstall the waterpump drive sleeve when you install the waterpump. Use some permatex white sealant on the threads of the mounting bolts and install them.
Fill the radiator tank up best you can. Start and get the engine hot, shut it down and fill some more. Repeat a few times and watch it over the next week or so.

 

Oh right, forgot he said it was a 92.

 

Everything between the opti and the ECM. The opti wiring is a common failure point.

p.s. Head over to the LT1 section on camaroz28.com. You'll get more diagnostic help and fewer idiots telling you to throw parts at it...

 

So I am an idiot because I said I would throw a $35 part at it because that is way cheaper than taking it to some dealer??? I allready admitted that was my mistake, didnt realize we were talking about a 92. Beyond that, an intermittant problem is NOT likely an opti. I have had 6 of them go out on various cars and have never had one intermittantly go in and out.

For the price of diagnostics at the dealer you can buy a mini scanner.

Incidently, I have been on camarz28 for as long as the site has been around, and although I dont go there much anymore, you arent gonna find anyone over there with any better advice.

SO keep your idiot remarks to yourself. And I got the origional post too with my quote. Read my next post, or all of them for that matter before you start spouting off at the mouth.

Oh and just so you know. Half the dealerships throw parts at them too. The differance is they charge you astronomical prices to experiment.

 

To put a closer on this thread (I hope) -

Corvette paramedics in Central New Jersey had the car when it acted up again. They agree with what most of your are saying - the Opti's High resolution signal has simply disappeared = a bad Opti. We are changing out the Opti and all of the wiring that comes from it. While in there - I'm doing plugs, wires, and a new water-pump as well. Car should be back in my hands by next week.

I don't expect to have any of the problems again! Not a cheap fix, but let's hope we got it and it's done acting up.

 

my car did this its a 92, turned out to be a bad conection at the iat sensor