Fuel cutoff settings- Softer rev limiter?

[GHuggins]

As far as the ecm side of the traction control settings goes - on Camaro's or Vette's running different sized rear and front such as drag race setups - I increase the torque settings for those still wanting to run traction control to keep traction from activating the brakes on and off while cruising down the road - it'll actually feel like a misfire going down the road when this is taking place... So by adding 100 or 160 to the tq input it helps keep traction from kicking in by allowing "some" seen wheel spin... Don't know the specifics and thinking about it now - it doesn't make a whole lot of sense, but that's what it seems like it's doing because if you have actual tire spin - it does still kick in...

[10_SS]

I'm actually very appreciative of you doing this I can prove time and time again that with a load on the engine a belt driven pd supercharger builds more boost just because its spinning up slower - explain that one when you figure out why they build 3 more psi hitting the rev limiter - perhaps the answer is one and the same I think it has to do with the physical air molecular makeup and how it flows as to a degree it has a weight, but no clue?

Maybe it's this: The combustion event creates heat, creates allot of expansion, then all that heat exists out through the exhaust with one push of the piston, and your left with cooling air which is shrinking, creating a bit of a vacuum which helps pull in manifold air. Now take away combustion, and you have no heat, so the additional vacuum inst there and piston intake stroke alone pulls in less air, creating more of a backup in the intake, resulting in more psi.

But, I also played around with the spark timing limiter and having it working great during wheelspin BUT I dont think -15deg timing alone will be enough to hold back, or is it healthy to, all that burning fuel from boosted LS3 alone.. I did play with it quite a bit but could never bring myself to floor it while limiter was set to say 3000rpm for longer than 0.5 seconds to see what would happen for the simple fact that all that heat and energy would be burnt in the exhaust manifolds.... I think throttle cut like you described here should be used instead. I'll have to play with these settings, thanks for relighting the candle, I was thinking there was no other good way.

[10_SS]

Been a long time since i looked at this code...

The two looked up values are added together for the final torque request. You are correct that making the numbers more positive (or more negative) as the RPM error gets larger will make the response faster.

The ECM will also switch from fuel/spark to ETC if the RPM limit timer exceeds the switchover delay table. The extreme limits are a hard fuel cut.

I played with this before but forgot.. With only Fuel Cut and ETC enabled, will the Extreme Cutoff always hold true.. or will the Extreme Cutoff always cut fuel regardless of any combination of Spark, Fuel Cut, ETC settings?

[Chris@HPTuners]

I played with this before but forgot.. With only Fuel Cut and ETC enabled, will the Extreme Cutoff always hold true.. or will the Extreme Cutoff always cut fuel regardless of any combination of Spark, Fuel Cut, ETC settings?

extreme will always cut fuel

[10_SS]

I have a whippled LS3 camaro and just want to confirm that this really works good.. at least good enough for a "pre limiter" and not to take place of the Extreme limiter in any way. gmtech16450yz is the man for sure, I know I would not have went WOT with boost on a stock LS3 experimenting with this, no way no how, especially with Spark OFF, fuel cut ON, ETC ON.. lol, this is completely opposite of my thought on safely limiting RPM on a boosted motor... but so far appears to be the way to do it. Now I get now knock at all.. but I still dont know what adverse affects it has long term if any. It works awesome under many conditions which is basically when your spinning wheels and hit the limiter in a manual trans car and sick of the fall on your face OEM setup. It also works good if you just want to floor it in neutral and let it float around the limit that you choose in the gear table... Neutral, stopped, does work good if you want to limit to something like 5500rpm when not moving but the problem is the tail shaft wiggles which triggers MPH, this makes the ECU think it's not in neutral and then uses 1st gear settings.. so it takes a bit of tuning to get it right, but definitely worth the time, thanks gmtech, really appreciate it.

My reason for really needing is is I have wheel spin on accel and it usually hits the limiter when I have 10-15mph difference between actual speed and rear wheel speed... then I shift and am low on RPM and power but I cant normally keep it below the limiter and since it cuts so violently RPM, power, and time, this is all I can do is shift. Now, if you look at the log, I am able to keep it floored, and the smooth RPM limiting keeps putting down power while the car picks up speed to match the front wheels... this is literally priceless. 3:54:38.120 - 3:54:38.600. I know its a short period of time but it starts with 15mph difference, ends at less than half of that difference just because I let off the gas.. before I would hit 6400rpm and it would basically shut down with 20+mph difference in rear wheel and front wheel speed, then I figure I should just shift and be low on RPM due to this... ANNOYING. I understand why these tires do this, that's so they can stick when your sliding in turns, but on street when you floor it they spin and quickly melt, but not as fast as drag tires or even DOT drags... they never acted like this.

Also notice I hit the limiter which I think it starts to predict the limit coming just a bit early and starts cutting fuel which is fine, so it feels pretty smooth as it tries to first use Throttle cut to limit and if it cant maintain with just that then it uses fuel cut which actually works really good... I was worried about knock but I have a whipple and none with all that boost.

Attached is just one snippet of a log at WOT and hitting my temporary 5500rpm limiter at WOT and it holding RPM while the car picks up speed to match (i have front and rear wheel speed logged) , then shifting and hitting it again. I should note I have these Goodyear ZL1 tires and they act strange as you cant tell it's spinning and the problem is I would hit the stock hard limiter and have to let off gas and shift, but then RPM's would be lower than normal since the car was never up to speed. Now... that problem is solved I can just hold it to the floor and wait until I stop feeling acceleration (while RPM is constant).

When I find the original poster/discover.. I'll link it here.. It was discovered about 2-3 weeks ago.

YOu can try it in neutral also, it will bounce pretty mildly. A couple times I floored it while moving in neutral and it hovered completely smooth at the limter just like my 2016 Silverado does.. no limiting other than ETC.. Other times when completely still or moving it would bounce a bit, but it is always using throttle to limit RPM when not in gear.. I think thats happening since I removed all of the 0's in the main limiting table and made it sharp the pull power if over revving, but slow and gradual to add power if under speed.

When hitting the limiter in gear with load (slower RPM increase) it tends to pull fuel while limiting RPM and I kinda like this sound vs the throttle limiter... not sure if the ETC still kicks in first and doesnt cut it then switches to fuel cut, but this is what I see. Wondering what affect the filter has on this.. mine is set pretty low.

Attachment 67691

Attachment 67692

Attachment 67693

[10_SS]

DAMNIT. I knew it was too good to be true. Now with these soft limiter changes that work great during the limiter action.. re-entry to WOT after shifting is DELAYED. This Sucks.

I noticed it while driving since I would buck a bit during throttle shift and WOT transition like power just wasnt there but under 1/10th of the second very minor.. well it's true.

Two logs attached.. one immediately before the changes were made showing immediate throttle response "134 WOT Fast Response" (pedal going WOT then instantly the blade moving but the rate is reduced on purpose - labeled as PE THrottle).

Second log attached labeled "136d Limiter Active but Throttle Delay" shows just a complete delay from start of pedal movement to start of the throttle blade movement.. cant have this.

Crazy to think the brain can notice this slight bog instantly though it's under 0.1sec.

Any ideas?

134 WOT Fast Response.hpl
134 Fast Response.PNG

136d Limiter Active but Throttle Delay.hpl
136d DELAY GOING WOT.PNG

[gmtech16450yz]

Hahaha! I'm glad I encouraged you to go out of your comfort zone and it didn't result in disaster! If you try this stuff out at a lower rpm I think it's pretty safe no matter what you screw up. I actually started my experimenting at a cutoff rpm of 3500! Then I moved it to 5000, then 6000 and now it's back at 6200.

I'm also thrilled that somebody had success with this. I think it's pretty cool, it's so much nicer to have a REDUCTION of torque instead of an ELIMINATION of torque. The stock rev limiters basically bounce from full power to no power, how is that a good idea? I actually went even further on my settings because when it's really easy to gain the power and rpm's back up, like in 2nd gear, the limiter was still giving back too much torque. I went kind of crazy and tried putting negative values all the way down the Delta table. It works! My theory was I wanted to make it not give ANY torque back once it's dropped it down initially. Even if the rpm's drop 800rpm below the set point, it still won't give it back any more torque. Even with the table with these crazy looking values, the limiter still gave back some throttle and torque. So far these settings are working even better, but I may find some part of it I can improve on later!

The hardest part is that all "rev limiter" situations are different. The amount of torque reduction when spinning the tires on wet pavement will obviously be different than if you're hooked up and hit the limiter on dry pavement. That and the fact that all of our cars have different power and will require very different values to limit the torque properly. So don't get discouraged if anyone has tried this and had mediocre results. This CAN be made to work better than stock. It just takes a little time to find the right values. When you do though, it's friggin awesome! Situations like holding a gear a little too long and losing ALL power because you hit the limiter will be gone. Instead you'll have a nice soft indication that it's time to shift! lol. Like I said before, not to mention the benefits for guys that drift. I would think this would be exactly what you would want in a drift car.

Thanks for posting your results 10_SS, I'm happy you've had success with it!

[10_SS]

gmtech16450yz I added some newer feedback right before yours to a new post probably while you were typing.. yea I started at 3500rpm too, worked up fast that's when I immediately noticed delay going back to WOT.. what do you think it could be? I think if this delay could be deleted then this would be perfect. It really would.

BTW, GM has since changed to a smooth rev limiter cutoff, i just think they are rushed and dont fine tune these types of details, either becuase it's just not ready or the code has weird side effects like I noticed after doing this.. not sure at this point.. One thing I do know is just like us, when you get a tune that works great then you change one thing weird things can happen, and when they finally get something working and validation approves it, last thing they want to do is change one simple thing.

[gmtech16450yz]

Hmm, are all the other tables except the delta and torque limit tables stock? How about trying all the gear rows as the same value in case it's having trouble realizing what gear it's in?

[10_SS]

I mean the only things I changed were these limiter tables...

Accell THreashold: all 0's except last column, 1000 top header = 500 in the cell
I did have Wheel Speed Limit set to 5000rpm at 0.0mph and 9.9mph then 7000rpm at 14.9mph, but shoudlht be a problem, changed all to 7000 now.

The one thing I haven't changed since I smoothed the Torque Delta table is the Cutoff RPM Hysteresis.. still at 300. THought about putting back to 150 that I tried early on.

Supposed to rain tomorrow... could be a bit before testing. It sure was nice flashing 5 tunes in 30mins driving earlier for instant feedback before losing the feel for what's going on.

[07GTS]

so the ecu even being manual still guesses the gear ? could u then use the neutral/park limit set to say 2500 rpm as a launch control ? or when the clutch is in during shifts at speed will it cut back to the 2500 ? thinking its neutral or will it use the gear values knowing its moving

[gmtech16450yz]

so the ecu even being manual still guesses the gear ? could u then use the neutral/park limit set to say 2500 rpm as a launch control ? or when the clutch is in during shifts at speed will it cut back to the 2500 ? thinking its neutral or will it use the gear values knowing its moving

I could certainly be wrong, but my understanding is that it simply uses the speed signal vs the rpm signal. IF that's the case, it would seem to me that it could get "confused" pretty often. I'm also guessing it disregards the calculations when it sees the clutch pedal is depressed. Otherwise it would also get confused seeing engine speeds and vehicle speeds that didn't directly correspond to a certain gear. That's why I rarely use gear choices in tables with manual trans cars. I usually put the same value in all the gear rows, that way if it does get confused, it won't matter.

[gmtech16450yz]

I mean the only things I changed were these limiter tables...

Accell THreashold: all 0's except last column, 1000 top header = 500 in the cell
I did have Wheel Speed Limit set to 5000rpm at 0.0mph and 9.9mph then 7000rpm at 14.9mph, but shoudlht be a problem, changed all to 7000 now.

The one thing I haven't changed since I smoothed the Torque Delta table is the Cutoff RPM Hysteresis.. still at 300. THought about putting back to 150 that I tried early on.

Supposed to rain tomorrow... could be a bit before testing. It sure was nice flashing 5 tunes in 30mins driving earlier for instant feedback before losing the feel for what's going on.

Haha! Don't you love it when you think you're actually figuring something out and then your results start not making sense whatsoever? I guess it's part of the fun of all of this tuning stuff! I've gotten so deep into things at times only to get more confused. I either stick with it and finally make sense of it or I just give up and figure it's smarter than I am!

[07GTS]

I could certainly be wrong, but my understanding is that it simply uses the speed signal vs the rpm signal. IF that's the case, it would seem to me that it could get "confused" pretty often. I'm also guessing it disregards the calculations when it sees the clutch pedal is depressed. Otherwise it would also get confused seeing engine speeds and vehicle speeds that didn't directly correspond to a certain gear. That's why I rarely use gear choices in tables with manual trans cars. I usually put the same value in all the gear rows, that way if it does get confused, it won't matter.

ok i might leave it then encase things go weird, but i have exhaust going on so ill be able to start tuning that and see how the limiter settings go thanks for diving into it a bit more and bringing some more understanding to the tables

[10_SS]

so the ecu even being manual still guesses the gear ? could u then use the neutral/park limit set to say 2500 rpm as a launch control ? or when the clutch is in during shifts at speed will it cut back to the 2500 ? thinking its neutral or will it use the gear values knowing its moving

The problem is you usually register MPH if you floor it while stopped, not sure about free revving but I usually get MPH showing when I rev high enough. I think this is from the tail shaft shaking, triggering pulses on the speed sensor. Then the ECU thinks your in gear and moving, changing your RPM limit. Allot of GM RWD cars do this, not sure about FWD. If it's an auto trans, if there is load on the driveshaft it might not do it, but if it's in neutral or flat ground no load it also vibrates.

[dreksnot]

Capture.JPG
^Talking about boost - this is a tough one with turbos. Throttle closes some and boost dies.

[10_SS]

disable ETC and try the fuel cut only... I actually like the way fuel cut sounds... Disclaimer if it blows up your motor it wasn't my fault.

It's actually been working pretty good for me I can floor it in 1st and second and assuming I dont have horrible wheel hop I can leave it floored and it redlines until I pick up speed... exactly what I've been wanting! Now if I can just get rid of this wheelhop (seen in the jagged RPM line on the ramp up to redline)

136g WOT RPM Log.PNG

[07GTS]

u still get wheel hop... when i fitted the blower it fixed my wheel hop issue, or what our Holdens were getting was the rear axles were different thicknesses so its stops the harmonics of wheel hop

[dreksnot]

disable ETC and try the fuel cut only... I actually like the way fuel cut sounds... Disclaimer if it blows up your motor it wasn't my fault.

It's actually been working pretty good for me I can floor it in 1st and second and assuming I dont have horrible wheel hop I can leave it floored and it redlines until I pick up speed... exactly what I've been wanting! Now if I can just get rid of this wheelhop (seen in the jagged RPM line on the ramp up to redline)

Hmmm... will give that at try. I was just concerned about lack-of-fuel and loaded up. So, if my motor blows, I will TOTALLY hold you responsible for my own actions and decisions!!! So, what does your two tables look like?
Adding some suspension to handle the hop is essential - you probably already know but our Camaros like trailing arms, toe links at a minimum to handle such debauchery.

[10_SS]

I have full BMR set up, BMR trailing arms and control arms, All Poly bushings including diff housing. Maybe it got a lot worse when I put the ZL1 wheels and tires on. After all the BMR stuff it's still will hops but definitely not as bad, which is why I think its the axles bending... too flexible

Camaro has different size CV axles, and that's where I think the problem lies actually.