'14 S/C C7 engine run-away to rev limiter

[jimxms]

Hi guys,

I have a C7 LT1 M7 with a D1X running a 3.5" pulley, Tial Q BOV with -2 spring, LT4 fuel system, MTI Secondary Low-Side Fuel Pump, Alky Control Meth, long tubes (no cats), forged pistons...etc

When I rev the car at a standstill, not in gear, above about 5000RPM, the engine runs away and hits the rev limiter. It will continue to bounce off the rev limiter until I switch the engine off.

Similarly, when I'm driving the car relatively hard and change gear around 5000-5550rpm, if I do not perform the gear change instantly, the revs run away up to 6500 and start bouncing off the limiter again. As soon as the gear change is completed, the revs drop back down again.

I've had a brief look at the HPT logs and it shows the desired throttle position as being a realistic number (not 100%) so i dont think its a problem with the pedal position sensor

In fact I'm not entirely convinced that this is a tuning issue as I've had my car tuned (from oem stock tune) by two different tuners and both have encountered the same issue.

I did wonder if my BOV wasn't capable of discharging all the boost that the D1X is making, and thus forcing open the throttle blade? But, the specs on the TiAL BOV (and yes it is a genuine one) say it is rated to 1800whp which I'm nowhere near making. Unless of course this is a S/C specific issue and the HP rating is for turbo apps?

Has anyone else encountered this problem? I'm reluctant to drop $250 on a secondary BOV to test my theory unless its the most likely cause.

[tunerpro]

When you take your foot off the pedal, either throttle follower and/or idle torque routines take over. They use the torque model to determine what the proper airflow across the throttle body should be. If your torque model is inaccurate, or your MAF sensor's calibration is wrong (particularly if the MAF sensor is reporting less than actual airflow), it would cause the symptom described here.

It's extremely unlikely the throttle body is getting over-powered, if the throttle body actual position doesn't match commanded, it will be into engine power reduced mode and set DTCs for the throttle control.

[jimxms]

When you take your foot off the pedal, either throttle follower and/or idle torque routines take over. They use the torque model to determine what the proper airflow across the throttle body should be. If your torque model is inaccurate, or your MAF sensor's calibration is wrong (particularly if the MAF sensor is reporting less than actual airflow), it would cause the symptom described here.

It's extremely unlikely the throttle body is getting over-powered, if the throttle body actual position doesn't match commanded, it will be into engine power reduced mode and set DTCs for the throttle control.

Thanks for the reply. I'll pass this on to my tuner and see if they can use the info you've provided to get to the bottom of it.

[jimxms]

With no reply from my tuner (anything could have happened in the past year I suppose), I may now be looking for someone to complete this tune for me. Any takers?

[TriPinTaZ]

pm me

[SultanHassanMasTuning]

you need to post your tune

[Alvin]

I would bet that it's a problem in the driver demand tables or the torque rate limiting tables.

I've made the same mistake

[jimxms]

Here's the last tune I received from the tuner and the log file associated with that tune. I'm not sure if the log caught the issue I've described, but I've been doing my best to avoid the car hitting the limiter

[Charlie540i]

Try to find a stock calibration for the car and do a compare. Check in torque management tip in mapped gear... the guy that worked on it before me copied and pasted all the parameters from a 8 speed car to a 10 speed and it was all messed up and it revved to the moon in neutral by just pressing the pedal.

[jimxms]

Try to find a stock calibration for the car and do a compare. Check in torque management tip in mapped gear... the guy that worked on it before me copied and pasted all the parameters from a 8 speed car to a 10 speed and it was all messed up and it revved to the moon in neutral by just pressing the pedal.

My tuner made a point of requesting my stock calibration when he started working on my car, so I'm pretty sure he worked from that. I will see if I can find that file again though and do a comparison.

EDIT:

No differences between stock and modified maps

[TriPinTaZ]

Any idea why the MAF is scaled so far below stock values? That is definitely throwing off some torque calculations. Your engine torque is way above your max engine torque which it should not be but I guess its working? As for the hanging throttle, your Driver Demand Increasing Torque Rate limits look suspect. Your Virtual Torque Tables haven't been touched either but I guess the car is staying at full throttle.

Do you have a 3 bar MAP sensor?
And your only complaint is a hanging throttle?

[jimxms]

No idea about the MAF scaling. I'm using the stock MAF with an IAT and BARO breakout harness. I've marked the location of the MAF (red), IAT (green), BARO (blue) in the image of my engine attached.

Yes I have a LS9 3Bar MAP (yellow location in pic).

It's more than a hanging throttle (unless that the term for it). I will let off the throttle at anything above 5000rpm it will continue to rev up to the red line.

Other than that issue though, the car is fairly well behaved. It can be a little bit jerky when cold, and also when the bypass valve closes at about 2500rpm the car surges a bit. But other than that its a freight train.



Some more notes about the car:

* The fuel rails you see are non functional at the moment and plugged up. They are for future expansion.
* I am running an LT5 95mm Throttle Body
* Vengeance Racking Stage 3 Cam
* Weapon-X Cylinder Heads with 10.7:1 CR
* LT4 HPFP, Injectors
* MTI Low side secondary fuel pump
* Alky control 100% meth

[veee8]

Try this. You will need to have the latest HPT Beta to open the file.

[jimxms]

Thanks veee8, I'm going to load that up and give it a test asap. It looks like you made quite a few changes, so thanks so much for taking the time.

[jimxms]

veee8 - I just gave it a try and it is MUCH better. Instead of hitting the limiter between slow changes it now seems to hold the the RPM. So If i change at 5k, it will sit there for a few seconds before dropping down. I'm assuming that this probably still isn't the ideal scenario, as the rpms will need to drop in order for me to make best use of the power band?

I also revved the car in stationary, and it got stuck at 6000 rpm (better than bouncing off the limiter) and sat there for a few seconds before dropping.

I logged the test drive if you'd like to check it out.

Thanks again for your work on it.
Edit: I just looked at the log and it said my TPS was at 30% when it was stuck at 6000rpm after i revvd at a standstill. Is that weird? I thought TPS was the pedal position?

[veee8]

Not really spending too much time on this, and didn't mess with fueling, but here is another one to at least try.
TPS is the throttle body, the accelerator pedal is the pedal.

[jimxms]

Not really spending too much time on this, and didn't mess with fueling, but here is another one to at least try.
TPS is the throttle body, the accelerator pedal is the pedal.

Thanks so much veee8. I can see you've made quite a lot of changes, so I really appreciate the time you've spent on this. I will try this one tomorrow and keep my fingers crossed

[jimxms]

veee8, WHAT DID YOU DO TO MY CAR MAN!!! Before my car was "damn thats fast", and now its "arrrgggghhh holy *&!@ thats fast!!!!!!!"

That second tune you sent me, wow! Not only have you totally fixed the rev hanging issue, but I swear you just added like 300whp! I just did a couple of 3/4 throttle pulls and its acting like my 315 R888r's are space saver wheels!

I'm definitely hiring you to hone in the rest of this tune, because you seriously know your stuff!!

[TriPinTaZ]

Crawford Racing for the win!