JHEBERT

You would need to have both stock and tuned files, open one and select open compare file. Differences will show instantly, do not alter any negative values. Other than that I have no idea why it would do this, but it’s disturbing for sure...

TurboLX

That's actually the runaway throttle safety check.

It's usually not a problem unless something else is wrong. Typically, the tuner hasn't modeled the airflow and torque models correctly, and the actual airflow gets driven up to a point that is way beyond what the driver really wants. If P0068 is tripped, the engine goes to REP (Reduced Engine Power) mode in an attempt to save it from the runaway as you describe. If this safety check is turned off, any mistakes in the rest of the calibration can lead directly to a runaway like this.

jimxms

Thats worrying! However, I've got two tunes from totally different (and well respected tuners) and both have P0068 disabled - so maybe this is quite common practice?

Today I actually managed to get a log of the over-rev issue. I played it back on HPT and this is what I can see happening:

- Rev matching disabled (so this doesn't seem to be the cause)
- Full throttle in 2nd to 5.5 - 6k
- Foot off accelerator and clutch in in preparation for switch to 3rd
- Throttle position starts dropping to 0%
- Revs begin to drop towards 5k
- Revs then start increasing up to 6k and beyond with TPS at 0%
- Change to 3rd

Basically if I'm slow in changing gear, or abort a gear change for whatever reason (like I did at the beginning of this thread), the revs self-increase, and I would assume that they continue to increase until it bounces off the limiter.

If I'm quick in changing gear It isn't as noticeable, but I can still hear it beginning to happen.

My tuner is going to diagnose it now we have a log, so fingers crossed I can report back what was done to resolve it.

TurboLX

Just because multiple "pros" made the same mistake, doesn't make it OK. I've seen LOTS of "professional" tunes with some very questionable practices employed, by some of the "biggest names" in the industry too.

If you have a datalogger, carefully watch the torque requests (both predicted and immediate) while this happens. Compare these to the reported engine torques and look for a discrepancy. Even better, look at the airflow and cylair while it's happening (IF you can believe their MAF, SD tuning, and fuel injector data) and see if that correlates. 99% of the time I see this, it boils down to the tuner taking shortcuts on very fundamental steps of the calibration process, then wondering why they got caught later. Newer GenV controls with the torque models are unforgiving of many of the shortcuts these guys used to get away with in tuning the GenIII/IV engines.

Mikec7z

well, i have no idea what caused it, but next time put it in neutral and hit the ignition switch and shut the thing down. Man, i would be mad. Sorry about your loss

jimxms

Does this help to confirm your theory:

Predicted Engine Tq: 106
Immediate Engine Tq: 637
Predicted Axle Tq: 268
Immediate Axle Tq: 2904
Pedal Position: 0%

This is right in the middle of it happening. My foot is off of the accelerator, and the revs are rising.

douglee25

Do you have any links (youtube?) that reviews the HOW and WHY of tuning these engines? More curiosity than anything.

TurboLX

In that case, the Predicted Torque (which is based on airflow) is very low compared to the immediate. This tells me that the torque models do not agree and opens the door for discussion as to why it might try to open the throttle to bring it back up toward the other. We'd also need to see the commanded torques to bring it all together. But in short, if the predicted is lower than commanded, don't be surprised when it opens the throttle to fix it. The system is just doing what it has been told by the tooner.

I have had plenty of live classes and a few DVDs on the older stuff. We have a mostly finished GenV video pretty much done that I'm waiting on my production team to finish. But honestly, this is not something so simple that a 5 minute YouTube video is going to properly explain it. Sorry. There are torque control specialists at the OEM who spend a career mapping this stuff, and then someone modifies it in the aftermarket and expects a quick fix. The best thing I can say here is that the better job one does on the absolute fundamentals of the calibration (fuel charge, air charge in MAF and SD, spark vs MBT, and throttle body model), the better one can expect the torque based controls to work. Every time you lie to the ECM about something in one of these, it gets compounded along the way with unpredictable results like this.

douglee25

Appreciate your insight. What do you recommend as a good read/vid on the fundamentals, not just torque mapping.

TurboLX

My videos are sold through Summit Racing Equipment if you want a solid demonstration of the fundamentals from an OEM Calibration Engineer's perspective. Keep in mind, these are not designed to just tell you what magical number to type into the box to make it better, but to teach you HOW the system works so you can calibrate for yourself on almost any new system if you apply the knowledge. The MAF and Virtual VE calculations are almost identical on the newer GenV systems to the GenIII/IV demos used in the videos, so they make a good starting point for anyone looking to do this right.

douglee25

Appreciate it.

Thanks.

Doug

TurboLX

I was able to put the OP in touch with a profesional shop that has some experience handling high power DI systems. Based on a few exchanges, we are narrowing in on what's really going on here.

A couple critical points for those reading along..

1) Of all the "pros" who touched his calibration, NONE of them had yet updated his speed desnity (Dyn_air, virtual VE) models. I cannot stress enough, it IS NOT POSSIBLE to PROPERLY calibrate an engine like this without taking the time to put in accurate virtual VE data based on steady state measurements. This number feeds the air per cylinder number AND the torque models. This stuff has been there since GENIV engines came out a decade ago. Lazy tuners are now getting caught for skipping steps.
2) His virtual torque values were also untouched. See #1 above. Don't act surprised when a torque based system responds incorrectly when you have a highly modified engine and a stock model (being fed by an also wrong air charge number)
3a) He also has a ported LT5 throttle body on a blow-through (centrifugal) setup. WHY? There is maybe 10hp to be had, but directly at the expense of throttle control down low. This is almost certainly contributing to his low throttle angle control issues when more air is leaking past the blade than the ECU knows. It has been my experience that the ONLY throttles that work in these applications are those with stock profiles (read: a completely stock LT1/4/5 piece or the Katech 103 that retains the blade shrouding at low angles) If you are pushing through the TB, you can get away with a smaller diameter at the same power level as compared to a positive displacement draw through throttle.
3b) If the "porting" of the TB affects the lower blade angles, EVEN MORE air gets pushed past the blade on a blow-through (centrifugal) application when it's "closed" because pressure upstream of the throttle is MUCH HIGHER than the normal atmospheric pressure. The ECU model doesn't know this and has trouble correcting., resulting in more flow than desired at the same low angle. It doesn't take much extra airflow to make enough torque to spin an unloaded engine up to 6000rpm.
4) If P0068 diagnostic had been left on, it would have caught the failures (for all the right reasons) and tripped the Reduced Engine Power condition as a safety measure. The previous tuners apparently don't care about liability.

This is the kind of stuff we teach in our classes and video all the time.

douglee25

Glad to see you're making some progress. At least it sounds like you're on the right track.

JHEBERT

No one touched his VE or edited his VTT? Now I am going to forever wonder who the “pro” tuners are that let it roll like that. I have learned a TON about our torque-based controllers in the last 18 months or so, and I understand how and why a lot of guys got left behind when it comes to tuning these things. Yeah sure, you have to get the AFR and timing dialed in...but that’s only 10% of what needs to be done to have all that new found power actually DELIVERED when you want it. Freakin’ torque ***** are hiding in the ECU and TCU, and just knowing WHAT to log goes a LONG way. You just can’t go along deleting codes and maxing values out, but that did work pretty good 20 years ago ( when we had software for logging, and another for tuning )

robert miller

I AGREE cant believe 90% of these people out here call themselves a tuner. Stuff like this is just crazy on this car that is why a big amount of guys when this c7 came out more than a few blew up a lot of guys motor & just to tell them sorry your motor gave out on the rollers... Robert

Ghostnotes

I'm an AUMATUER tuner, I have only done about a dozen or so GEN V, not counting my own which I practiced on for several months and the only forced GEN V so far. The first time I saw this code It was OBVIOUS what it was for. It in a roundabout way, it lets me know if I am headed in the right direction.

spinkick

Would anyone be willing to look at my tune after I supercharge to make sure it had been done professionally? Stuff like this scares me.

Ghostnotes

When you post it, post a scan along with it. That helps to tell the story better.