Dies during coast-down to idle

[96GS007]

Looooong time lurker, well before I ever registered or bought the MPV13.

I'll cut to the chase. I have a 2019 Corvette Grand Sport with the LT1 and 7spd manual transmission. It has the following mods....

- Ported cylinder heads
- Nick Williams 103mm throttle body
- Mamo ported MSD intake manifold
- AFE cold air intake
- LG full length headers
- G-sport (GESI) Gen 2 cats rated at 500hp/bank
- DoD deleted
- GPI SS3 LT cam (pic of cam card below)
- RPS Billet Carbon Street Twin Clutch w/Aluminum Flywheel. This setup is ~42lbs lighter than stock. The revs are awesome and Active Rev Match works fantastic. However, I have to believe the lack of mass is what's contributing to my issue

Dyno: 570 rwhp / 493 lb-ft of torque

The idle is fine, LTFTs look very good. Nothing wonky with the timing that I see. The Idle External Load table lines up very well with the delivered engine torque. It drives very well and as a track car it does outstanding on the road course

Issue....When slowing to stop (coasting in gear or using the brakes) and I push the clutch in, the RPMs rapidly drop and 25% of the time the engine dies.

Help Needed: Can someone point me in the right direction regarding what table(s) and/or factor(s) to work on please? It seems like I just need the rpms to not drop as quickly. As soon as I go "clutch in", the rpms drop so low the engine often can't recover


GPI SS3 LT Cam Card.jpg


Attachment 132438


Thank you very much for any assistance you can offer. I've searched but have come up empty.

[GHuggins]

Have you tried increasing your adaptives and then cutting your decreasing rate limits in half? You can also increase your base airflow some more and then you're going to want to get your idle timing up and torque down just a touch.

[Ben Charles]

VT and VVE will fix it

[96GS007]

Have you tried increasing your adaptives and then cutting your decreasing rate limits in half? You can also increase your base airflow some more and then you're going to want to get your idle timing up and torque down just a touch.

Thank you for your feedback! I've tried the following without success ....

- Moved the Adaptive Idle / Integral Min back to the stock settings and left the "Integ Max" table alone. The Integ Min was half the stock values previously.
- Increased the base airflow within the MAF Airflow vs Frequency table a minor amount using the LTFT percentages as my guide
- Bumped up the timing in the idle areas by a couple degrees and blended it

Wasn't sure where/what table to adjust torque so I left that.

Long story short, the car was not happy with the above

[96GS007]

VT and VVE will fix it

Looking at it, I think the VT table needs to be nudged back towards stock. I'm a total noob with this so it'll be lots of minor experiments. Any recommendations regarding what parameters to log? I'll date myself...the last real tuning I did was with the Gen 2 engines...LT1 and LT4. Gen 5 is a foreign language to me

[GHuggins]

This is something close to what I meant. Ben recommended doing the VVE on top of what I recommended - not a bad idea to fail the MAF and dial that in too.

These corrections may overshoot it or may not even help, but torque should be lower and idle timing a little higher. It should also help slow the rpm drop.

[96GS007]

You absolutely nailed it! Sent you a PM

Thank You!!!

[GHuggins]

Replied to the PM. Just glad I could help you out. You'll want to put about an hour on it then see if it needs any tweaking.

[96GS007]

Replied to the PM. Just glad I could help you out. You'll want to put about an hour on it then see if it needs any tweaking.

I have about 90 minutes of a variety of driving situations on it with the car sitting overnight and morning temps of around 70 to it sitting nearly 8 hours in a parking and outside temp at startup in the mid 90s, and the IAT >100*

Out of all that driving, it did die once (after sitting 8 hours and it being hot outside) but otherwise has been flawless. I logged a bunch of parameters to see if there was any knock, how the timing looked, LTFTs, etc. To this rank amature it looks pretty darn good. I'll drive it a bit more next week but to not wonder if it's going to die every time I stop is a huge relief!

The latest log is attached.

[GHuggins]

I'm going to say that your VE and lower MAF cells might clean that up. Looks like it's really lean when it stalled (as the rpms were dropping) You can set the tune up to idle lower and dial your MAF and VE areas in for the lower rpms better. Other than that, it wouldn't hurt to have idle torque a touch lower - this will drop with the VE tuning and timing looks great.

[96GS007]

I'm going to say that your VE and lower MAF cells might clean that up. Looks like it's really lean when it stalled (as the rpms were dropping) You can set the tune up to idle lower and dial your MAF and VE areas in for the lower rpms better. Other than that, it wouldn't hurt to have idle torque a touch lower - this will drop with the VE tuning and timing looks great.

Thanks Greg! I'll go into the MAF and VE and get those squared away and then adjust the torque in the Airmass A and RPM A tables a couple percent downward


Screenshot 2023-06-03 235335.jpg

Screenshot 2023-06-03 235520.jpg


Or conversely should I just go into the Virtual Torque tables? Trying to be deliberate since as I mentioned above I'm still way up high on the learning curve with the Gen 5

It'll be a week or so before I can test it out. Caught a nail on the way home from work last Thur so I need to get that taken care of. Always something....

[96GS007]

Been away for a bit and between catching a screw in a tire and rain, I haven't been able to get the car out much but did so yesterday and today. I made a few final adjustments to the MAF table and the External Load table. The car hasn't died and the fuel trims and timing look pretty good to me. I'm sure this is one of those things that I could tweak forever, but at this point I'm happy with how it runs. Doesn't die, little to no surging, and the data looks good. I need to finish the VE tables but that's more of a "nice to do" sort of thing vs mandatory.

Big shout out to Greg for his assistance!

I attached my log from the first drive today. Prior day logs are similar. I've been trying to do 2 drives/day 4-6 hours apart in order to hit cold start and warm start

[GHuggins]

Just glad I could help. If you want fueling and torque to stay the same from cold start to hot engine idle you'll need to dial your density table in. You'll probably have to tweak the VE and MAF again slightly after that, but shouldn't be to bad to do with it already being that close. If you want the method for doing that just shoot me an email. I have a step by step for doing it that I give out to my customers. It's time consuming, but in your case you could probably just make minor changes driving around using the math formula for it.

Everything else in that log looked pretty good.

[96GS007]

Sent you an email! Thanks Greg!

[96GS007]

I've continued to play around with things, both VT and VVE, as well as some very minor tweaks to idle and such. Long story short I think that I'm in pretty good shape and figured I'd share my results.

Fuel trims look good vs VVE, and MAF (screenshots below). On occasion it'll die if I'm trying to gently edge the car forward or "clutching in" at a very low rpm such as 1100 so I think those conditions are more a function of the lightweight flywheel and clutch which are ~45lbs lighter than OEM and me, particularly when trying to feather a clutch that doesn't lend itself to feathering. The only real street driving this car sees is to/from the track so I can live with this.

My latest tune is attached.

I tried to attach the log but it seems to be too big. I'll just mention the outside air temp today in Dallas was a balmy 109*. Beside highway cruising I did some stop & go driving and saw IATs at one point exceed 130* In the log is a few places with some knock retard but I think that's really due to the heat. Something to keep an eye on.

Anyway.....feedback welcome. It seems like there are a lot of people that put in big cams and lightweight flywheels/clutch components that battle this so I wanted to share where I ended up.

Screenshot 2023-08-04 220247.jpg

Screenshot 2023-08-04 220136.jpg

Edit: Broke the log file into 3 pieces.....Highway, Stop & Go, End of Drive. Right at the end of the drive is where it dies once...probably due to me

[GHuggins]

Take a look at your torque model - 1200 rpms on the arimass side - now look straight down it - your 1200 and 1800 rpm points are higher - smooth these down by selecting from 2000 to 900 and going up from the bottom a couple of rows. That will bring throttle down slower. Now for the map side - 1200 - raise it back up to stockish or slightly higher. From everything I've found out the map side will mimic - ever so slightly - the VE table. AS for the idle region itself you need to fail the MAF and dial each model into one another.

Then if you have user defined parameters there is another pretty important table that needs changing too. It's pedal progression. As best I've found out so far pedal progression directly influences idle torque and timing, decel rate, rev matching, dfco entry, neutral revving and throttle behavior in general. Seems like DD does jack squat for most of that. If you have user defined parameters Will_974 on here can find the coding and build the table for you to edit through her online store.

You can also slightly alter and use idle controls from this one - it's a factory car cal. For throttle closure you're going to want to lower your current left hand side of the throttle adaptives and then increase spark control at the same time.

The above corrections should fix what stalling you still have.

[96GS007]

Thank you for your help!

Attached is the updated file if you wouldn't mind taking a look. Unfortunately as you can see, "prime tuning hour" for me is after the little one is asleep so I may not be fully understanding what you said

I adjusted the Virtual Torque table on the airmass side in the 1200 range and extrapolated around that to smooth things out a bit between 950 and 2400 on all the tables. On the MAP side, I dropped in the stock cells and then smoothed those as well since just dropping them in looked really rough.

For the Idle Adaptives, both Immediate and Predicted under Speed Control I lowered the left hand side. Not quite as much as the stock file you sent...about 60% of the way there.

I don't have a "User Defined Parameter" license, so I can't change any of those items.

For spark control I wasn't sure. Below are pics of the current table and the OEM table values. I wasn't quite sure if those are the values you meant and how far to take them

R23 file:
Screenshot 2023-08-05 005139.jpg

OEM values:
Screenshot 2023-08-05 005200.jpg

Thanks again!

[GHuggins]

Sorry didn't mean those tables. Spark adaptive is your "immediate" adaptive table. Throttle adaptive is your "predictive" adaptive table.

You smoothed the wrong end of the airmass tables - meant the lower or "negative" value region - there's a hump there you're trying to get rid of at 1200 and 1600 going to idle. Raise the upper side back up - lowered there can cause trans problems.

Map side - raise it up more on the 1200 and 1800 upper cells. Won't hurt to stick up then drop back down.

[96GS007]

Hi Greg,
Sent you a PM

[96GS007]

Got it sorted! After I sent the PM, I held my nose and jumped in with both feet. Just finished a 40 minute drive. Lots of stop and go and I was intentionally clutching in at very low RPMs....frankly driving just like when it was stock. I also spent a lot of time doing stop & go where I'd gingerly edge it forward or just barely get the car moving enough where the clutch was fully out and then I'd clutch in. In all cases, 0 stalls. The final test was getting it uphill and turning to get into the garage which also takes some finesse. Did that multiple times and again...0 stalls

I'll keep testing..."1 data point does not make a trend"....but I'm cautiously optimistic!

After a few more logs I can nip and tuck as necessary in the idle regions and perhaps have it idle at 850.