Joe_G

PROBLEM SOLVED THANKS TO NICODEMUS.

SEE POST 8 AND 18 BELOW - MAKE SURE YOUR TUNER KNOWS ABOUT THIS, IT IS NOT OBVIOUS THAT YOU WOULD NEED TO CHANGE ONE CELL IN THIS SMALL TABLE BURIED IN THE PROGRAM.

I have an unusual problem. At 5800 rpm in 2nd gear only, my car has a bad miss - it is way down on power. It feels like it is hitting a rev limiter, but will continue to rev to the 6500 redline. There is no miss in 1st or 3rd or 4th gear at all.

This problem started after I put in 390 gears, headers and an LS2 Edit tune. I had the tune taken out and the stock tune put back in, and it still does it. My tuner said he saw a few misfires on #3 when he scanned it with his Tech 2 but not enough to worry about. And I understand the computer does not scan for misfires over 3000 rpm anyway so it would not find these.

I changed plugs yesterday and tested resistance in all wires, all wires were the same and the plugs were not cracked and looked consistent and properly colored. Unfortunately, the problem is not solved. I was thinking perhaps bad valve spring but that would manifest itself in all gears I would think and this doesn't. Car has only 9000 miles on it.

Any advice from the guru's out there?

kp@hp

automatic or 6spd??

Joe_G

6 speed. Z51 package, MZ6 trans.

Zig

did the 'tune' also change the rear end ratrio ? any chance you're hitting the limiter in second due to the new ratios ?

Joe_G

No, with a manual you don't have to do any adjustment to the speedometer for new gears so nothing done there. And I've got the factory stock tune back in and it's still doing it, so I've taken the tune out of the equation.

But please keep the ideas coming! Somebody much smarter than me will figure this out I'm sure. That's the power of the Forum I'm counting on!

Zig

i wasn't exactly referring to the speedometer in particular.

i was referring to the rpm calculations the ecm uses for the rev-limiter.

it was my understanding that even with a manual transmission you would need to make adjustments in the ecm related to gear ratios.

would not the speedometer read the 'incorrect' actual speed if all you did was drop your tire size ? why wouldn't you need to make adjustments accordingly as a result of a gearset change ?

with a different gearset you will hit the limiter much sooner.
with the 'new gears' at what rpm would redline occur in second gear ?

i would suspect as much. if adjustments weren't made for the new gearset the problem would persist, eitherway.

Joe_G

Hey Zig,
You may have something, I'm don't know much about the actual mechanics of tuning, just what I've read here. The car hits the real rev limiter at 6500 in every gear without exception and the speedometer still works perfectly with or without the tune. The vehicle speed sensor reads off the driveshaft I think. And the real rev limiter on an LS2 is "soft" compared to the LS1, which hits hard when it kicks in. This will be hard to describe - the LS1 goes "baa-baa-baa" against the rev limiter, the LS2 goes "bzzzzzz". In either case the engine does not rev past the limit.

My 2nd gear symptoms sound very similar to the LS1 rev limiter - except it continues to rev. Thus I characterize it as a miss, or perhaps valve float, but if it was valve float it would be every gear (in my experience with older cars). This mystery has quite a few of my local buds stumped! I wanted to get the forum's thoughts before I started replacing parts ***** nilly, like the PCM or taking it into the dealer.

Nicodemus

I had the same problem when I had 4.10 gears installed.
http://forums.corvetteforum.com/show....php?t=1384795
There is a table that lets the rev limiter kick in early. I fixed it with HP tuners. I never realy got an answer on what the table was for but the problem is gone.

k-line

I am having the same problem (along with some others) after doing 4.10s. But it happens to me in 1st and 2nd. But not in 3rd. If this were the case ^ wouldn't he mod shops now about it?

Joe_G

Nicodemus, you are the man. How I missed your post I don't know, but I will get this information to my tuner right away!!!!

THANKS!!!
Joe

Nicodemus

Your welcome. Glad I could help.

Nicodemus

You would think so wouldn't you. No one had a clue when started to call shops to get my problem fixed when I had the problem. That is why I bought HP tuners, I got tired of people telling me it was the tach as if I cannot tell the sound of the engine only getting 6000 rpm. I had it figured out in 5 minutes with HP tuners, It really makes me wonder how much time was spent by the tuners trying to fix the problem.

tluck

I have 462.5 RWHP and 4.10's in my 2006. I was told by my tuner Cartek that the motor is reving faster than the stock tach can culculate, therefore, you hit the rev limiter before the tack indicated redline. My 2005 had 3.90's and had the same problem. Install a shift light and your problem will be solved.

Zig

i would guess the one included in the hud would lag accordingly ??

Nicodemus

Mine did not have anywhere near that much power at the time and that was not the issue. The sound even sounds different than the rev limiter and the problem was fixed when the value was change in the table. The problem does not happen in first gear. First revs faster than second.

Joe_G

Oh yes - that thing lags even the real tach in my C5 experience. It's too small to see anyway for me. I had a shift light in my H/C C5 and it ran exactly with the tach. I don't have a shift light in my C6 but truthfully, after a while you know what to listen for and when to shift. I glance down at the tach, particularly now that my car will start sputtering at 5800 precisely, so I don't hit that false rev limiter. My car WILL rev to 6500 in 2nd, just sputtering all the way from 5800.

I've sent Nicodemus' info to my shop - he was happy to hear this! Remember, these LS2's are still pretty new to being tuned, with some additional complexities compared to the LS1's that have been out there since 1997.

Joe_G

Nicodemus, I have EXACTLY the same symptoms as you. I found that if I sneak up to 6500 in 2nd, it doesn't do it, but if I am accelerating at 1/2 throttle or better, it hits what sounds like a LS1 rev limiter every time.

I can't tell you how happy I am if this is the fix. I put in headers, gears, and a tune and only gained .2 and 3 mph due to the requirement of this short shift at 5800. What a huge disappointment. If this works, I really owe you a beer or two!!

Thanks,
Joe

Joe_G

Nicodemus, thanks again. This one tiny change (one cell!) on a table buried in the programming (and not very obvious) made all the difference in the world. I don't know how you figured this out but THANKS!! My car is running great now.

If anyone is getting gears in an 05 they should make sure their tuner knows about this one esoteric change. I doubt anybody touches that table otherwise.

XmentalPilot

Great story! Way to hang in there and sleuth out the problem!!!

XmentalPilot

You may want to "revisit" this issue with Cartek since this fix has been discovered.... I doubt that the "slow tach" syndrome was the real issue.