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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

1991 L98 Pinging on Shell 93 Octane

Old 09-17-2017, 06:34 PM
  #41  
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Originally Posted by billschroeder5842 View Post
Ha! How true.

But being this is Texas, the cops just ask if you can spare an extra beer and then ask you to be careful.
Don't "Bogart" the beer
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Old 09-18-2017, 02:16 PM
  #42  
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Well now my mechanic friend volunteers to adjust the timing. I will report back with the results.
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Old 09-19-2017, 12:20 AM
  #43  
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Originally Posted by koritz123 View Post
Well now my mechanic friend volunteers to adjust the timing. I will report back with the results.
From what to what? You can't simply adjust the timing at one point. It's all or nothing on an L98
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Old 09-19-2017, 08:15 PM
  #44  
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Originally Posted by aklim View Post
From what to what? You can't simply adjust the timing at one point. It's all or nothing on an L98
Since he's volunteered for it that means now I don't have to buy a timing light yet.
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Old 09-22-2017, 12:25 AM
  #45  
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Well the mechanic friend adjusted the timing from 9 degrees BTDC to 5.5-6 degrees BTDC.

The only time it pings now is once in a while when I lay on it in first gear from a stop it pings for maybe one to two seconds and it's so light you can barely hear it we had a really strain our ears and it doesn't happen every time and he said that was light enough not to even worry about.

***
Problem is he wanted to drive the car so bad he could taste it so it was his birthday today and I said okay(he has to drive my cars to his house sometimes when he works on them so I thought maybe it would be good practise but I really didn't like it) So he did U-turn in the middle of the road and it's dark and runs the corvette down an embankment and has it stuck on a hill sideways and couldn't get it off the hill. When he went backwards all it did was scrape the whole underneath of the car on the passenger side and then he throws it into reverse and starts backing up with the front tires on the pavement and the rear tires in the Grass at a considerable speed and I said don't you want to see if there's a fire hydrant in the grass behind you first before you do that?

Afterwards we looked at the car in the dark with a flashlight and the air dam on the front didn't look any the worse and I didn't see any front body scrapes underneath on the body in front of the air dam and I didn't see any on the side of the car that was wedged on the grass or the back of the car. I looked to see if the side of the car(passenger side) that was wedged on the embankment halfway part on the road and the other half in the grass sideways to see if it was damaged then I didn't see any damage there. So now I'm going to take it and have somebody put the thing on a lift and see if I can see anything we missed.

The underneath is scratched quite a bit and I have really low riding mufflers and exhaust system which I'm sure is really scratched up. And also he noticed that the front of the car underneath the chassis is all scratched up by the air dam.

Plus he shifted it so jerky slamming it into gear and said he wanted to shift it without the clutch cause it would be fun and I told him to do that on his own car.
When he was 17 he had a hot car and lost his license for a year so he stopped driving hot cars after that because he couldn't control himself. He told me now he was older so it wouldn't be a problem he's in his sixties.

If it wasn't for the fact that he has repaired my cars for 15 years and saved me tons of money I would NEVER HAVE LET HIM DRIVE MY CAR.

I should have stayed in bed today.

Last edited by koritz123; 09-22-2017 at 12:52 AM.
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Old 09-22-2017, 01:31 AM
  #46  
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Yup, you learned the hard way. Never let anyone drive your car. Your friend is an idiot.
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Old 09-22-2017, 07:38 AM
  #47  
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I'm really not sure what to say....

At least you fixed your detonation issue.
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Old 09-22-2017, 09:16 AM
  #48  
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Originally Posted by koritz123 View Post
Well the mechanic friend adjusted the timing from 9 degrees BTDC to 5.5-6 degrees BTDC.

The only time it pings now is once in a while when I lay on it in first gear from a stop it pings for maybe one to two seconds and it's so light you can barely hear it we had a really strain our ears and it doesn't happen every time and he said that was light enough not to even worry about.
3 degrees won't solve that problem. 3 degrees might be enough for the ECM to mask that problem sometimes.

Old school way is to hear it. So how do you hear it when the ECM has compensated for it by retarding the timing? What you hear is what the ECM cannot compensate for.
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Old 09-22-2017, 09:16 AM
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Originally Posted by billschroeder5842 View Post
I'm really not sure what to say....

At least you fixed your detonation issue.
I disagree. He hasn't fixed the issue. It is better hidden is all.
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Old 09-22-2017, 09:33 AM
  #50  
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Why is 3 degrees advanced not enough to cause spark knock?
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Old 09-22-2017, 09:38 AM
  #51  
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Originally Posted by Kevova View Post
Why is 3 degrees advanced not enough to cause spark knock?
What I am saying is that people have changed their timing by a few degrees and noted "No problems", IOW, I don't hear anything. That said when you can hear it, it is VERY late already. The ECM will retard timing if it hears knock regardless of what YOU hear or don't. So until it cannot, assuming a functioning KS, you probably won't hear it. So it might be knocking but you cannot hear it. Only way to do this is to see what the KS is reading.

Imagine this. If I am playing music in the other room and you wear ear muffs, am I still playing music although you don't hear anything? If I turn it up loud enough, it overcomes your ear muffs and you hear it. Turn it down a notch and you won't. Still, doesn't mean I am not playing music, does it?

Or the other way is "If a man makes a mistake and a woman is not around to know it, is he still wrong?"
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Old 09-22-2017, 11:34 AM
  #52  
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The knock sensor is intended to pick up the heavier knock of detonation. Detonation is the more violent knock that tends to cause engine damage. The ESC will retard the timing 20 degrees when it picks up detonation. Spark knock can also pre-ignition which is the more audible annoying rattling. The ESC does not always pick it up. Pre-ignition does not cause engine damage unless it is prolonged. Having to run 93 in what was originally a 9 to 1 engine is curious. A compression test could give an indication of compression ratio. GM built some engines that required premium only. They also found out owners weren't willing to buy it. They would use the cheapest gas they could find. The correction was ecm reprogramming or to back off the initial timing 4 degrees which would remove the spark rattle. Later the ecm was able to determine octane rating and adjust accordingly. As engines were updated the compression ratio was reduced so it was more tolerant of regular grade gas. So the 3 degrees might be the correction. The OP needs to investigate how the engine was rebuilt.
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Old 09-22-2017, 01:55 PM
  #53  
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I can try and do a compression test.

Just took it out for lunch and I might be hearing things but it sounds like I can still hear an occasional ping in first gear .I turned on the air and I thought I heard it ping just a second or two and then also other times, although I can't replicate it every time.

Last edited by koritz123; 09-22-2017 at 02:52 PM.
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Old 09-22-2017, 03:12 PM
  #54  
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Originally Posted by koritz123 View Post
I can try and do a compression test.

Just took it out for lunch and I might be hearing things but it sounds like I can still hear an occasional ping in first gear .I turned on the air and I thought I heard it ping just a second or two and then also other times, although I can't replicate it every time.
You could easily be hearing LOTS of things. Your fuel injectors working could easily be confused with a pinging sound under acceleration with exhaust and wind noise.

I'd really be spending more time inspecting your under carriage. Your off roading adventure could have easily knocked a few things around, so I'd get it up on a lift. I think your pinging is now small potatoes.

Last edited by billschroeder5842; 09-22-2017 at 03:12 PM.
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Old 09-22-2017, 04:07 PM
  #55  
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You really don't have to all the cylinders 1 or 2 provided the readings are close. I believe Wallace Racing has a chart for cylinder pressure and required octane. I think the dished pistons were replaced with flat tops.
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Old 09-22-2017, 04:21 PM
  #56  
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In my experience, tune-up and electrical parts are not usually considered an engine rebuild. I mean, you can add tune-up and electrical parts at the same time you do a rebuild. But an engine rebuild usually includes major internal hardware such as pistons and rings, valves, lifters, pushrods and rocker arms, timing set, journal bearings, etc. Sometimes new connecting rods, camshaft and crankshaft, etc. depending on their specs and wear.

OP, do you know what was done to this motor in the rebuild 500 miles ago?
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Old 09-22-2017, 04:47 PM
  #57  
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Originally Posted by billschroeder5842 View Post
You could easily be hearing LOTS of things. Your fuel injectors working could easily be confused with a pinging sound under acceleration with exhaust and wind noise.

I'd really be spending more time inspecting your under carriage. Your off roading adventure could have easily knocked a few things around, so I'd get it up on a lift. I think your pinging is now small potatoes.
I have noisey fuel injectors and took a stethoscope to them to make sure the noise was coming from them so I'm pretty used to the kind of noise they make but maybe their sound changes on acceleration.

I think I have an exhaust leak now since the off roading last night. I have to get it up on a rack soon. Car drives straight and no leaks under the car.
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Old 09-22-2017, 04:53 PM
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Originally Posted by DGXR View Post
In my experience, tune-up and electrical parts are not usually considered an engine rebuild. I mean, you can add tune-up and electrical parts at the same time you do a rebuild. But an engine rebuild usually includes major internal hardware such as pistons and rings, valves, lifters, pushrods and rocker arms, timing set, journal bearings, etc. Sometimes new connecting rods, camshaft and crankshaft, etc. depending on their specs and wear.

OP, do you know what was done to this motor in the rebuild 500 miles ago?
From the seller:
Seals and gaskets through out the engine. Valve seals both heads. Checked for head warping. Heads straight as an arrow. Hash marks visible on cylinder walls and no sign of ridges. No wear on seats or springs. He removed the entire engine from the car and cleaned it up as well. I have the pictures.

I also have a long, long list of other parts electrical and otherwise replaced at the same time.
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Old 09-22-2017, 04:54 PM
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Originally Posted by Kevova View Post
You really don't have to all the cylinders 1 or 2 provided the readings are close. I believe Wallace Racing has a chart for cylinder pressure and required octane. I think the dished pistons were replaced with flat tops.
I'll try and do a couple of cylinders and report back.
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Old 09-23-2017, 02:41 AM
  #60  
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Originally Posted by Kevova View Post
The knock sensor is intended to pick up the heavier knock of detonation. Detonation is the more violent knock that tends to cause engine damage. The ESC will retard the timing 20 degrees when it picks up detonation. Spark knock can also pre-ignition which is the more audible annoying rattling. The ESC does not always pick it up. Pre-ignition does not cause engine damage unless it is prolonged. Having to run 93 in what was originally a 9 to 1 engine is curious. A compression test could give an indication of compression ratio. GM built some engines that required premium only. They also found out owners weren't willing to buy it. They would use the cheapest gas they could find. The correction was ecm reprogramming or to back off the initial timing 4 degrees which would remove the spark rattle. Later the ecm was able to determine octane rating and adjust accordingly. As engines were updated the compression ratio was reduced so it was more tolerant of regular grade gas. So the 3 degrees might be the correction. The OP needs to investigate how the engine was rebuilt.
I agree with what you said. I am thinking that the ESC, assuming it is working, is doing the retard TO AN EXTENT. How much retard is another question. That said because it has an effect, it muddies the water, so to speak and we can't be sure how much was taken out without looking at the logs. The 3 degrees might, I suspect, push it MORE into the window of correction but not all the way which is why he hears it sometimes. Thoughts?
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