Dipping idle after coming to stop

[Alvin]

Pretty sure the help file says the MAF will not work.

A well tuned SD setup will drive better especially on a setup like this because of reversion.

[phuz]

Pretty sure the help file says the MAF will not work.
A well tuned SD setup will drive better especially on a setup like this because of reversion.

Good to know. I've just always been told that MAF has better drivability / SD is better for high HP setups.

[bk2life]

always been told that MAF has better drivability

in all seasons, elevations and soccer moms, yes, the maf has better ability.
SD tuned in hot summer, will not drive very well in humid raining seasons, or really cold winter.
But, if you can make a few changes in your tune, youll be fine.

[reubone]

Screenshot (89).png
Try lowering the highlighted table to about half the stock value. This will also a lower minimum injector pulse width. Could be that on decel it is getting too rich and causing the oscillation due to the injector not being able to close enough. Just something to try.

[blindsquirrel]

The speed density custom OSes can still use the MAF just like stock, or even in 'MAF only' if you set up the Dynamic like that. The tooltip thing/official description is incorrect.

[phuz]

Screenshot (89).png
Try lowering the highlighted table to about half the stock value. This will also a lower minimum injector pulse width. Could be that on decel it is getting too rich and causing the oscillation due to the injector not being able to close enough. Just something to try.

I'll give it a shot, but this also occurs when coming to a stop.
Take another look at this log file: perfect example of it happening while I'm coasting to a stop in neutral.
Look around the 7:40 mark.

28-mar-2023.hpl

The speed density custom OSes can still use the MAF just like stock, or even in 'MAF only' if you set up the Dynamic like that. The tooltip thing/official description is incorrect.

That's good to know! Is there any tutorial or writeup on this, especially if the tooltips aren't accurate?

[reubone]

Screenshot (92).pngScreenshot (91).pngScreenshot (90).png
Try these changes and lets see what happens

[reubone]

What I am attempting to do here is to give the idle circuit a chance to catch and stabilize your idle sooner

[phuz]

What I am attempting to do here is to give the idle circuit a chance to catch and stabilize your idle sooner

OK, I'll give these a shot. Unfortunately, I caught this after going out for a drive and now it's parked for the night.

[phuz]

Incorporated some of these changes and no dice. It seems better for the most part, but there are still occasions where it drops way too low such as yesterday while turning into a parking spot. I'm surprised it didn't actually stall out, but it dropped to about 200rpm. On recovery, it did not overshoot the idle; instead, it just came back up slowly. Unfortunately I was not datalogging at the time.

[phuz]

If my Base Running Airflow is set for 13.5g/s, and in my datalog I see the Idle Desired Airflow is only 8-9g/s, I'm wondering if this is why I'm getting dipping. After throttle blips (0mph), I never see default to 13.5g/s. With a STIT of 0% right after the blip, I would expect to initially see it at 13.5.

01-apr-2023.hpl
2001 Corvette_with_Procharger_idle_changes.hpt

[reubone]

2001 Corvette_with_Procharger_idle_changestry.hpt
Try that

[phuz]

2001 Corvette_with_Procharger_idle_changestry.hpt
Try that

Funny, I was actually looking at that thinking about making the proportional/integral negative error a bit more aggressive.
Thanks, I'll give this a try. Unfortunately rain is just about here so it won't be happening today.

[phuz]

@reubone, loaded most of those changes, and it's a tad better, but I also raised my idle from 850 to 900 and bumped up the BRAF a smidge.
There was one instance yesterday where it dipped to 700rpm

One thing I am still trying to find out is how the STIT is calculated. Under Idle -> Airflow -> ST Adapt Airflow Max, I have it set for 0.5 g/s, yet the second I come off throttle, my STIT value is -3.2 g/s.
And also, where is Idle Desired Airflow coming from? It's not the BRAF, or BRAF + STIT.

I also have now tied in my wideband as maybe this will assist in some of the fueling issues as my fuel trims at idle are still much higher than I would like them to be. I'm also experiencing a couple spots where I see it go lean momentarily under cruising, but I'll save that topic for another thread.

Yesterday's log:
03-apr-2023.hpl

[reubone]

Ok load the tune that your currently running so I can see where all our settings are currently sitting. Also, add injector duty cycle to your channel list please. I believe that the negative adaptive is coming from trying to run such a high base idle spark advance. This log looked way better but its crazy rich on decel so there a couple things that I want to check.

[phuz]

I've stepped aside from the dipping idle issue so that I could work on tuning my MAF and VE, because as mentioned earlier this in thread, my idle AFRs are too rich. On each iteration of logging & adjusting today, I reduced the VE value for the idle cell(s), yet the idle continues to stay rich. You can see the commanded AFR is right around 14.5 yet it doesn't really get close to that.
I've been logging the injector pulse width, too, and noticed that I never see it get any lower than 2.1ms. My minimum injector pulse is 0.122ms and none of the other injector settings appear to be holding it back, either.
It's as if the PCM knows it needs to go lower, but something is preventing it.

2001 Corvette_with_Procharger_VE_tuning.hpt
10-apr-2023-vetuning-5.hpl

[reubone]

2001 Corvette_with_Procharger_VE_tuningtry.hpt
The min fuel milligrams in the transient table can cause this issue. I think i mentioned these earlier. After this adjustment, you may find some areas too lean. Please let us know

[phuz]

2001 Corvette_with_Procharger_VE_tuningtry.hpt
The min fuel milligrams in the transient table can cause this issue. I think i mentioned these earlier. After this adjustment, you may find some areas too lean. Please let us know

I don't want to mess with any of the transient stuff until the VE table is good, which I'm still working on. (but curious how anything under the transient tab would have anything to do with idle AFRs?)

Take a look at the fuel offset for voltage. It was over 1ms for the 14v range. This was from a data sheet provided by A&A Corvette. I reached out to Fuel Injector Connection and they supplied me with an updated sheet which has drastically different values, so I plugged that in, and essentially had to start my VE table over again, but it's made a huge difference. It's now 0.27ms for the same cell region of the offset map, and I'm able to get the idle region of VE pretty close so far. I'm sure I'm going to have to dabble with transient settings due to the added supercharger, but I'm trying to do baby steps right now.

[phuz]

Here's a log from earlier.
With VE somewhat dialed in for the idle region, a hot start of the car will show lean AFRs, but at the end of the drive, in the same idle region, they are rich.
The only thing I see different is the IAT (90 at startup / 72 after drive). Maybe I'll have to add some After Start IAT enrichment when I'm done with VE.

11-apr-2023-vetuning-5.hpl

[phuz]

Current log and tune. Was OK for the most part for several days of driving around. Didn't really see it drop too much below 750 at any point, until today when pulling into the garage.
Dropped to 270rpm (4:48 in the log). One of the things I am logging is the Idle Air Control Position. This value never seems to change from 310. Is that because of the ETM?
Not really sure what else I can be doing to catch it when it drops this severe.

2001 Corvette_with_Procharger_2bar_VE_tuning.hpt
25-apr-2023-vetuning-4.hpl