HELP! can't keep off the rev-limit/fuel-cut

[white2001s10]

1998 C5 vette LS1 A4
SD OL tune, but I don't think it makes a difference with stock tune either.

I'm using EFI-live for tuning & scanning,
trying to raise the shift points beyond 6300 RPM, and it goes into fuel-cut.
Raised rev-limits to 7300, still fuel cut at 6400 RPM ...WTF?
Several flashes at different settings... putting normal, hot, and cruise all at the same numbers, but no difference.

Once the car ran with the higher shift points perfectly and really liked the higher RPM, but the next tries (nothing changed in the tune) all hit fuel cut especially during the 2nd to 3rd shift.

I have tried several times, and looked through the tables and cannot find anything that seems like it would cause this.

I don't ask for help often, but this time I'm at a loss and need a hint at least.
Please throw out suggestions. Hopefully this isn't one of those "vette features"

[dbaxter_ss]

Where are you changing them,
Under Trans Calibration\Shift at RPM\Upshift ?

LABELS Selection
Parameters Value
{D0940} WOT 1->2 Shift RPM, Normal 5300.000000 RPM
{D0941} WOT 1->2 Shift RPM, Performance 5300.000000 RPM
{D0942} WOT 1->2 Shift RPM, Hot 5300.000000 RPM
{D0945} WOT 2->3 Shift RPM, Normal 5300.000000 RPM
{D0946} WOT 2->3 Shift RPM, Performance 0.000000 RPM
{D0947} WOT 2->3 Shift RPM, Hot 5300.000000 RPM
{D0950} WOT 3->4 Shift RPM, Normal 5300.000000 RPM
{D0951} WOT 3->4 Shift RPM, Performance 0.000000 RPM
{D0952} WOT 3->4 Shift RPM, Hot 5300.000000 RPM

or
Engine Calibrations\Rev Limiters

LABELS Fuel Cut-off Limiters in Gear (RPM)
In-Gear Cutoff Fuel In-Gear ReEnable Fuel
First Gear 6800.000000 6400.000000
Second Gear 6800.000000 6400.000000
Third Gear 6800.000000 6400.000000
Fourth Gear 6800.000000 6400.000000
Fifth Gear 6800.000000 6400.000000
Sixth Gear 6800.000000 6400.000000
Seventh Gear 6800.000000 6400.000000
Eighth Gear 6800.000000 6400.000000
Not In Gear 6800.000000 6400.000000
Reverse Gear 6800.000000 6400.000000

[white2001s10]

Shift points in the first one,
and rev-limit in the second one,
so both.
Shift point set at 6300
rev limit set at 7300
hits rev limit at 6400

:nixweiss:

edit: see since I can't get it to rev to 6400 or more, I had to lower the shift point down to 6300.
the shift points are working fine... or at least trying to. It's the rev-limit that's kicking in for apparently no reason.

[dbaxter_ss]

Strange? The A4 GTO I have setup with the rev limits at 6800 and trans cal upshift by VSS and have no problems.

Those are the 2 areas I know to change RPM limits.

[white2001s10]

I'm not sure changing the upshift to VSS instead of RPM would do anything. It already shifts fine based on RPM.

It just seems the PCM thinks it needs to cut fuel at the wrong time.

:help2:

[dbaxter_ss]

Well its a vette, does it have ETC?

Or maybe even VSS failed RPM limit?

LABELS ETC Controlled RPM Limit (RPM)
Value
First Gear 9000.000000
Second Gear 9000.000000
Third Gear 9000.000000
Fourth Gear 9000.000000
Fifth Gear 9000.000000
Sixth Gear 9000.000000
Seventh Gear 9000.000000
Eighth Gear 9000.000000
Not In Gear 9000.000000
Reverse Gear 9000.000000


LABELS Selection
Parameters Value
{B2201} ETC Rev Limit Enable Disable
{B3330} Fuel Cut-off in P/N 6200.000000 RPM
{B3331} Fuel Re-enable in P/N 6199.023438 RPM
{B3332} Fuel Cut-off, Low RPM 41.992188 RPM
{B3333} Fuel Re-enable, Low RPM 50.000000 RPM
{B3301} Engine Overspeed Time Allowed 0.025000 Seconds
{B3322} VSS Failed RPM Limit Upper 6200.000000 RPM
{B3323} VSS Failed RPM Limit Lower 6199.023438 RPM

Do you have a log of this cutting out and the tun, I will take a look, another set of eyes may see something.

[white2001s10]

VSS fail = 7000 RPM

ETC limiter is disabled, and I'd see it on the scan if the TPS changed, and it doesn't. I do see a sharp lean spike on the wideband log when it hits fuel cut.

[white2001s10]

Ok well I lied, the TPS % does change from 99.6% down to 99.2%, and up to 100% sometimes, but since the change is so small I discounted it as a problem.
i worked on it all day today and failed to solve the problem.
The rev limiter either don't work, or it does work uncontrollably or almost randomly sometimes.

Shaka when the walls fell :bawl:

[jfpilla]

Have you tried logging transmission converter clutch slip speed, Trans input speed and Trans output speed? See if it's slipping.

[white2001s10]

Have you tried logging transmission converter clutch slip speed, Trans input speed and Trans output speed? See if it's slipping.

I'm willing to try that too, but please tell me how that would make the limiter malfunction.
The limiter is now set to 7800 RPM, and the logs show the limiter cutting things off either at 6400, or 6000 RPM. There's no way the engine is spinning faster than that or I'd be able to tell.

[jfpilla]

I'm willing to try that too, but please tell me how that would make the limiter malfunction.
The limiter is now set to 7800 RPM, and the logs show the limiter cutting things off either at 6400, or 6000 RPM. There's no way the engine is spinning faster than that or I'd be able to tell.


It won't. Sorry, I should have read it closer.

[jfpilla]

Does it do it without the EFI cable plugged in?

[white2001s10]

I didn't try that.

[white2001s10]

It does show these error codes though.
C1281 C $28 TCS
C1288 C $28 TCS

I think at least on of these is for the TPS mounted on the gas pedal.
I could see that messing up the shifting maybe, but not the rev-limiter.
The shifting seems to work well.

besides having the MAF codes as well from running SD mode.
The car has always had this problem, even two years ago when first trying to raise the limit with Edit, and I'm pretty sure it was happening even with no cable hooked up to the ALDL.

[jfpilla]

I'm reaching here:
I've "heard" that 98's can have tranny problems if the MAF values are changed. Wonder if SD has some role if the tranny needs the MAF?

[white2001s10]

well 2.5 years ago it had the problem then too. It was only converted to SD mode one year ago, almost exactly.

I lowered the P/N rev limiter to 3000 RPM, but it never worked.
It reved well past 3000.
I tried putting the P/N limit up to 7800 too, but fuel cut still happens around 6400.

:nixweiss:

[TAQuickness]

in your first post, you imply at one time you could run all the way to the 7300 cut off. Have you tried putting that tune back in?

[white2001s10]

Once the car ran with the higher shift points perfectly and really liked the higher RPM, but the next tries (nothing changed in the tune) all hit fuel cut especially during the 2nd to 3rd shift.

It only went up to the higher shift point of 6600 1>2 and 6400 2>3 once without fuel cutting, not the 7300 Rev-limit.
Yes I definately tried that tune again a few times, but it kept hitting the limiter on the 2>3 shift.

I think I know what the other guy is talking about with the vette and unhooking the MAF causing the power-loss thing, but this isn't the same problem at all. This problem isn't even consistent.

It makes me wonder if there's something wrong with the transmission module or shifter switches. Sometimes on the data-log it doesn't seem to know what gear it is in and says unknown or neutral.
I would've figured if that was the problem then the P/N limiter would apply, but I've since set that up to 7800 and problem still there.

[Scoota]

Just out of curiosity, would there be a slim chance you have a valet switch hooked up and the engine is fuel cutting in valet mode.

Just a thought.


Cheers Scotty.

[white2001s10]

Where in the world would something like that be? :nixweiss:

[jfpilla]

I think I know what the other guy is talking about with the vette and unhooking the MAF causing the power-loss thing, but this isn't the same problem at all. This problem isn't even consistent.:cheers:

I'm not talking about the Maf Rationality Test. I've never seen a good explanation, but it is said the 1998 MAF is involved in torque measurements and shifting. But if you had the problem with the MAF hooked up that's not it. Unless you had changed MAF values.

[Scoota]

Ahh, thats right, the 98's don't have CO's as yet, It's the Aussie in me to have thought otherwise. Sorry guy's.

Cheers Scotty.

[white2001s10]

Rev-limiter parameters:
ETC Rev Limit = enable/disable
Fuel Cut-Off in P/N = 7800
Fuel re-enable in P/N = 7700
Engine overspeed time allowed = 3.0 seconds
VSS failed RPM upper limit = 7800
VSS failed RPM lower limit = 7700

Fuel Cut-Off in gears: all set to 7800 C/O and 7700 re-enable

Abuse management parameters:
A/M in gear upper RPM threshold = 8000
A/M in gear lower RPM threshold = 1500
A/M P/N upper threshold = 7300
A/M P/N lower threshold = 1500
A/M time = 0 seconds
A/M VSS threshold = disables at 2 MPH

[white2001s10]

Anyone want to take a look at the bin ? I could mail it tonight after work.

Who's going to be the first to get a CO for a 1998 vette?
This one sure needs it.

[Techfan]

TT I am very interested in this thread also as I have the same setup.

[dbaxter_ss]

send it along I dont mind.

[white2001s10]

send it along I dont mind.

pm me with your email please.
.. that is if you meant for me to send the bin.

[dfe1]

It may be that you're chasing the wrong thing. You don't list any details about the engine, so this may be way off base, but you may be experiencing valve float/lifter pump up. When you hit a rev limit caused by a fuel cut, it's a very distinct "hard" limit that shuts the engine off, until engine speed drops to the re-enable rpm. On the other hand, if the rev limit is caused by the valve train or an ignition or fuel system problem, the engine just kind of "hangs around" near the rpm "limit". Try setting your limiter to 6200 rpm and the re-enable to 6000 rpm. That will put the limit below the speed at which you're having the problem. Then test it and log the drive. You should feel rpm go to 6200, then the engine will die for what seems like an eternity, then come back to life when rpm drops to 6000. If that works, you know the limiter and re-enable control are operating properly. Then raise the limiter to 6500 and the re-enable speed to 6300 and repeat the test. If you don't get the same type of response at fuel cut and re-enable, that pretty well proves the limiter isn't the problem. You might also check the fuel filter. If fuel pressure takes a dive, you can also experience a "soft" rpm limit-- you should be able to see this in the O2 voltage. If it would help, I'd be happy to take a look at your tun and log files.

[white2001s10]

No answer yet.
ttt.

[Kool C5]

No answer yet.
ttt.
Did you ever figure this out? I have had the same problems for years.
I have a 97 Vette and have had 3 engines, several gear changes, run CL and OL with MAF. It always seemed worse with lower gears (410 & 373). I always thought it was a nitrous problem, but I now have a LS7 in my car that is N/A.
I can't raise the shift points any higher than about 6200 to 6300 rpm with out
having the rev limiter/fuel cut out shut the car down. I could live with this when I was using Nitrous, but would like to rev the LS7 higher.
I have read about this problem before over the years, but have not got to the bottom of this. I would like to figure it out before I die:Eyecrazy: