Lost PART of my tune?

[orcuttg]

On a basically stock 2010 SS (LS3) Dec 31 I installed a flex fuel sensor and had it tuned to run E85 on 65 lb injectors. Before the tune obviously it ran very rough on gas. After the tune it ran great for months on both E85 and 93 octane.

I replaced my spark plugs a week ago with NGK Iridium, and since then I hit the rev limiter at 5000 rpm.
video: https://photos.app.goo.gl/ifi4af2B3hv62sLbA
Unless I'm moving; when I go to neutral on the highway it revs up to redline:
video: https://photos.app.goo.gl/VoxqMjWzD71NVN4U7
No idea if it's related to the spark plugs, or to my installing a radio a month ago, or unrelated to either.

It hasn't gone back to factory tune, because the engine runs fine with the larger injectors, on both E85 and gas.

Has anyone ever heard of a car losing part of its tune?? Totally mystified here.

[pyroguy]

I'm not an expert on this subject so take this advice for what it's worth, $0.02.

I believe the standing still RPM's are limited to somewhere around 5k if you're not in at least neutral. If you're in park and/or you don't have your clutch pushed, possibly with the car in gear (I'm an auto guy, sorry), that the car won't rev any higher hence the difference on the highway.

[xc_SS/RS]

It has a rev limiter that kicks in while you’re in neutral or park because revving an engine with no load isn’t a good idea

Your tune is fine and you didn’t lose a portion of it

[orcuttg]

Thanks. It's not a question of "in park" because it's a manual. And it USED to go past 5000 when I was trying to do a burnout. Now that it won't go past 5000 when stopped, so it stalls whenever I try to--what do we call it during the pandemic?--sanitize the tires.

[ariZona28]

Have you tried turning traction control nannies off? Maybe try a few different settings for "research and development" purposes.

[Greenhornet2]

Wouldn't be the tune. Likely cracked a plug or two and it's misfiring. Or the plugs are not right for the car. There's some threads around on what plugs to use I don't know off the top of my head. Or you possibly damaged plug wires when you removed them. I'f did was noticed right after changing the plugs this is likely your issue.

[Kajun]

Put the original plugs back in. It's possible they are too cold for your setup.

[orcuttg]

Thanks for all the input. I'll check the connections. Unfortunately I don't have the original plugs anymore.
My expectation would be if I cracked one or damaged a wire and it was misfiring I could hear it, or I'd get a check engine light.
The oddest thing is it revs fine when the car is moving. I'll probably take it back to my tuner this week and learn what he can see on his computer. I'll post the results in case someone later has the same odd issue.

[Greenhornet2]

If you aren't having an issue while driving then it's probably fine. I thought it was the other way around i misread. Pretty sure the rev limit is lower in neutral but i'm not positive I've never revved over 5k in neutral

[mikeman]

I know you probably don't want to buy another set of plugs, but if it happened right after you put the NGK's in , then that has to be it. Or, something happened right after you did that. You can always check each plug wire for proper resistance with a voltmeter. Also, maybe one or more coil packs are getting weak. Just a few ideas.

[Kajun]

I misread also. If it doesn't do it in gear I don't think you have a problem.

[orcuttg]

It was the tune. There's a table that limits the revs at 0-10, and 10-20, and 20+ kph. Both the lower ones were set to 5000, the upper to 7k. They're all 7k now and it's much better

[mikeman]

You didn't realise that until after you replaced the plugs? Sorry, I'm now confused.

[orcuttg]

Originally Posted by mikeman

You didn't realise that until after you replaced the plugs? Sorry, I'm now confused.

Well, I was confused too, which is why I asked the board.
As for how the solution (tuning table) fits into the equation: Maybe the new plugs for some reason are putting out slightly LESS power? or the tires were broken in and were a little stickier? But in either case:
1. After the plugs were switched out (not BECAUSE the plugs were switched out) I was unable to burn the tires, which caused me to look more closely at
2. the rev limiter stopping at 5k rpm when stationary, but going up to 7k when moving.

The underlying recent change (plugs not as good as I hoped? tires sticker?) is still there, but they dyno that benchmarked my car 12/31 is no more, it burned up in a fire, so I may never know whether there was a power difference.