a coil on the way out is another possibility.

the reason I mentioned about checking your spark is it is relatively easy to do, and if you are getting a consistent, strong spark, you should be able to cross that off the list,

HOWEVER,

I fixed a friend's 4-wheeler. It had been into shops and none could figure it out. Sometimes it would run, and sometimes it wouldn't, mostly wouldn't. Being a few years old, it had hardly any time on it and had run out of warranty.

I pulled the spark plug and by accident, turned it upside down and then back over. I noticed the ceramic was loose and would sometimes drop down and seal off the spark. Replaced the plug, and Bob's your uncle.

I mentioned this as to not overlook the overlooked. Sometimes it is the simplest component that should NOT have failed, does. That plug had all the shops chasing their tails. When they pulled it, the ceramic would slide back in and look and function correctly, but put back in, the ceramic blocked the spark.

 

Thanks for video. Will try timing light tomorrow

plugs have been changed several times over the years. This problem I am trying to correct is at least 6 years old

 

I didn't mean the plugs. Just an example that it could be the simplest part causing the issue, and to look at everything, even those parts that aren't supposed to fail.

 

SBC harmonic dampers have been known to slip the outer portion due to rubber deterioration. Is it possible yours might have done that?

which will put the timing mark in the wrong place relative to the marker....

 

Will check balancer

 

Don't lose hope. If it still runs good and drives good, it's an annoyance and not worth getting rid of her. I know the feelings of frustration you have, but when you find it, it will probably be something really simple.

Any way to get live data on these OBD1 cars?

 

Multiple Options.

 

..... 7,000 miles in 6 years isn't helping … has this car been run at highway (65-70) speeds for more than 20 minutes ? … have you ever stuck your foot in it ? … Take it for a long drive down the interstate …..

 

Yes to your questions 😄

 

I don't want to sound like a smart ***, but don't you have a Corvette shop or Corvette tech nearby? Maybe it's time to bite the bullet and pay someone for their experience.

 

Not going to pay shop hundreds of dollars to find something I should be able to. Not going to spend any more money on this car. Either I fix it or it goes

Please only respond if you have an idea of how to fix my car

thanks in advance

Mike

 

I did put vacuum gauge on it several times, and if I remember it was a tad over 15. I did notice that gauge did fluctuation a very very small amount in a rhythm

 

Hello again Mike!

If you had a broken spring your car would not sound good at all as it would only be running on 7 cylinders. I don't think it is anything mechanical causing the noise or misses at idle. I have a fleet of 8 cars in our fleet and whenever any one of them starts idling a bit roughly I simply drop a bottle of B&G 44K into the tank and the problem goes away. 99% of the time it solves the rough idle and improves the performance. Start with the easiest stuff, B&G is sold on Amazon and it works very quickly.

If you have a tapping noise or some other strange noise at idle try to isolate where it comes from. Noises at idle that don't amplify when the engine speed rises are harder than ever to solve.

Having replaced several CTS' you should have no problem verifying the output of the one you have in the car right now. Check it and post the numbers you got for us. Use pins to go into the wire and measure what it is seeing while the car is running. When done seal holes with RTV or tape or whatever you choose.

I had a Cadillac STS that came with the Northstar engine. It had a small miss at idle all the time and the dealer could not solve it, they told me it was normal and to live with it on a $60 k Cadillac. The miss became more evident at 70 mph in high gear with the A/C on. I showed them the miss on printouts and they could do noting about it. Finally I realized that the A/C system was cycling very quickly and it turned out that the A/C system had a bad error in its software. The hysteresis was too narrow which cause the compressor to kick back on while still under pressure the computer re-engaged the Compressor which cause a sensation like a miss at speeds. Cadillac made me a new prom for the car but they also removed my "overdrive" the lock up torque converter was disabled. This on a car that gets 12 mpg was not a good move. Cadillac put the overdrive back and widened the hysteresis allowing the compressor to work normally.

If you have any data that shows your car while it is missing I would love to see some of it.

Still listening out here! Lets get this Corvette back on the road running the properly and let it makes it's owner happy with owning a Corvette. It sounds like he is in need of "Miles of Smiles" only provided by genuine Corvettes!

Best regards,
Chris

 

Now that’s something I would not have ever thought of. I can do data logging using tuner pro rt and post it. It’s just so darn hot here in Texas I can hardly stand working in my garage. I did head gaskets a few years back and didn’t know when to take a break and had to go to ER With mild heat stroke. But I will try these great ideas and post back on each one.

 

Mike, I feel your pain with the heat. I ended up putting a window unit in my garage so I could work on the car during the summer months. With the humidity and heat in south Mississippi it gets damn near unbearable to work in a garage. Good luck with you problem, keep the faith and you will eventually find the issue. it's got to be something simple.

 

..... EGR delete ? … did you use block-off plates ? Has the top cover on the throttle body been re-gasketed ? Check the EEC solenoid ? disconnect and plug the vacuum hose to the brake booster ? PCV working ? How is your HVAC air vent selection working ? Cruise control work ? A.I.R. pump and diverter valves ? MAF relays and wiring ? ESC plugged in ? and ESC is working ? HEI in cap coil ground strap in place ? HEI in cap coil hold down screws have not pierced the top inside of the distributor cap ? Correct coil for the distributor ? A/C compressor cycling ? …..

 

Egr is deleted. Checked everything you mentioned except ac cycling on and off. Will check that out. I have done smoke test and propane test numerous times. I have taken off the big frisbee plate. I wondering if It might have a bent push rod since the problem has been there from the time I bought. Thank you very much for your response

Mike


car. Car is in such great shape otherwise, not a single leak, new transmission

 

Did a little today until heat drove me back into house

AC is not engaging off and on
went to use timing light on plug wires, but wouldn’t you know it, timing light quit working

 

Got a new timing light today. I connected to each plug wire and I could see nothing out of the usual. Each one seemed to flash at a steady rate. If this is correct, then I believe the electrical side of engine is not the problem. As the temperature here in Texas starts to cool down I will continue to try the things suggested from each of you

thanks

Mike