More issues on 2015 Z06

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Originally Posted by ShawnC7

Unfortunately read this after doing all of the work.

Just finished swapping out the plugs and wires and data logging. The original plugs were gapped properly, all had carbon build up, at least 2 were fouled with oil.

Ran a compression and leak down test on all 8 cylinders. All cylinders held pressure at 225-230psi, no outliers no leaks.

Data logging showed the bad news. Still misfires on all 8 cylinders. Couldn?t determine if it was less than before, still had a dozen or more misfires in a 10 minute drive. Still seeing less to no misfires on WOT than idle/cruising speed.

The mechanic/knowledgable fellow who was helping me out looked over the tune and said with it being misfires on all 8 cylinders it?s likely the tune, and the timing is way too high. He recommended bringing it to a new tuner and having it retuned from the ground up and knock the timing back a few notches.

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Can you data log it again? This time pay attention to your timers at the bottom. Point out a time stamp or multiple time stamps where you feel it or where you think you're having misfires? That way maybe someone here can "see" literally what you're talking about.

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Originally Posted by edcmat-l1

Then, in addition to that, I have them pull the plugs, take a piece of cardboard and poke 8 holes, 2 sets of 4, stick the plugs in the holes and with a sharpy number them on the cardboard. Then take close up pics for me.

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Is there any possibly you can do this ^^^? Even if you didn't keep track of which plug goes with which cylinder, can you take some close up pics and post them here? I'd like to see all of them together if possible.

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Originally Posted by blindsquirrel

This needs someone competent who can go hands-on with this car. Further tuning won't fix it if it's been hurt from a previous bad tune.

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Would there be a reason a new tune wont fix it if it seems like the engine is in good health?

There is a shop a few hours away that has tuned several 1000whp+ street/drag cars that have lasted well into the 80k+ mile mark with little to no issues with nearly all hard driven track use. I got several recommendations to see them for tuning and was told they would make it run right.

But obviously if there is a reason I should avoid paying to retune I would like to know. But from what Ive heard that?s my best option. Let me know

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Originally Posted by edcmat-l1

Can you data log it again? This time pay attention to your timers at the bottom. Point out a time stamp or multiple time stamps where you feel it or where you think you're having misfires? That way maybe someone here can "see" literally what you're talking about.



Is there any possibly you can do this ^^^? Even if you didn't keep track of which plug goes with which cylinder, can you take some close up pics and post them here? I'd like to see all of them together if possible.

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Ive got the spark plugs, but we did smear them on a towel to separate carbon from oil that?s moreorless how we determine some were indeed fouled. The fellow helping me said it?s likely a non-issue and is a result of the lack of spark and running rich and something about crank case (I?m 20 and know little about mechanical problems, so sorry if my explanation is a little poorly worded). I can still do this, but not sure if the smearing/wiping negates what you are looking for specifically.

In terms of data logs, I only have what one of my friends set up for what it?s looking for. I do have some data logs already from after the spark plugs replacement, from what I?ve been shown by friend, he?s having me look at Long Term and Short Term fuel trims and misfires which he setup to report on the data log. To be honest I?m not sure what I?m looking at half the time.

Lastly for when I ?feel misfires? I can?t honestly say I even know what to feel for. 6.2L Corvettes already feel choppy to begin with so identifying little misfires as in idling or cruising are next to impossible for me since I?m not even sure what I?m supposed to feel for. Only reason I knew there was an issue to begin with was because I had an issue where I was initially running rich to the point it was shuttering on idle kicking out black smoke from gas so my friend set up the data logging with misfire checks and we noticed the insane amount of misfires.

Let me know if the pictures of the spark plugs are still wanted, and if there?s any tips to identifying misfires. I can post the data log here too.

What have you seen so far that would give you good confidence that the engine is in good health? Your report of the leakdown & compression tests up above are complete gibberish, leakdown results are a number in percent, and whether a compression test 'holds' or not is because there's a little Schrader valve in the gauge so that it'll record the peak. Never seen anything but a diesel that would do 230 PSI. You think it's possible the chamber and piston tops are caked up with a 1/4" thick layer of oil and carbon, if that's a real number from a real compression test?

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Originally Posted by blindsquirrel

What have you seen so far that would give you good confidence that the engine is in good health? Your report of the leakdown & compression tests up above are complete gibberish, leakdown results are a number in percent, and whether a compression test 'holds' or not is because there's a little Schrader valve in the gauge so that it'll record the peak. Never seen anything but a diesel that would do 230 PSI. You think it's possible the chamber and piston tops are caked up with a 1/4" thick layer of oil and carbon, if that's a real number from a real compression test?

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When it comes to the exact PSI I was told that the number doesn?t matter unless it?s super low. As long as all 8 cylinders are reading within 5-10% of each other then we know that a cylinder isnt damaged. All 8 cylinders read at around 230 psi, even if it isn?t truly 230psi we know that they are all giving similar readings of compression. As for leak down, We did hold the compression tool for a minute on each cylinder to see if it went down, and the needle only moved 1-3psi. If you?re saying that it automatically holds it at its peak value then that was a miss on my part.

Honestly though, I can?t imagine any damage being so consistent between all 8 cylinders that they would simultaneously read the same compression while having damage AND running somewhat decently.

There are misfires being reported on all cylinders so obviously something is wrong, but the car can still idle, cruise, and pull just fine. We aren?t seeing any catastrophic events or anything warranting immediate mechanical attention (yet) so I sincerely think there is not something as serious as engine damage.

I also want to take a second to say, appreciate the helpful feedback. I dont want to come off as someone who sounds like he wants to be right and ignore the people trying to help. I can genuinely say probably everyone in this forum is more knowledgeable than me. I?m just trying to connect what I see in person to the feedback I?m getting to see where we can troubleshoot next, and what im seeing now doesn?t sound like an unhealthy engine.

On that note, just to confirm suspicions, what is the most logical/time and cost effective method to check for more signs or symptoms of engine damage? Previous commenter suggested a bore scope inspection so I am inclined to start there.

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Originally Posted by ShawnC7

Ive got the spark plugs, but we did smear them on a towel to separate carbon from oil that?s moreorless how we determine some were indeed fouled. The fellow helping me said it?s likely a non-issue and is a result of the lack of spark and running rich and something about crank case (I?m 20 and know little about mechanical problems, so sorry if my explanation is a little poorly worded). I can still do this, but not sure if the smearing/wiping negates what you are looking for specifically.

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You have a late model fuel injected car that runs clean as a whistle for the most part. If you have shit on your spark plugs that you have to smear off to tell if it's carbon or oil your shits got issues. How many more times does someone have to say it?

Oil diluting the air/fuel charge drastically reduces the knock tolerance. If the plugs are crapped up then everything in the chamber and likely the backsides of the valves is crapped up just as bad. 230 PSI is too high for a pump gas street engine - most engines with high static compression have enough camshaft duration that cranking compression will still be in the normal range of 150-180 PSI. A leakdown tester has two gauges, and the test result is a percentage (2% leakdown, 7% leakdown...), it is not a 'put some air in and see how long it will hold pressure' test. This ain't like big truck air brakes.

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Originally Posted by blindsquirrel

This needs someone competent who can go hands-on with this car. Further tuning won't fix it if it's been hurt from a previous bad tune.

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I agree with this. From the sound of it and the logs, it looks to me like it has or had a terrible tune in the car and now the damage is done. Take it to someone that can do a true compression and leakdown test. Hell even here at the dealer I only charge like 250 to do that. If your plugs are getting fouled out that fast, then theres some sort of damage done. Even heavily carbon deposited DI engines wont foul the plugs that fast......just run like crap on a cold start.

:banghead::banghead::banghead:

Lots of this going on in here.