Help with Coastdown RPM - 2004 GTO - 408 - 239/247 cam

[ViaBellator]

I find myself wanting to say something like "Hi, long time listener, first time caller" LOL - I've generally been able to figure out any and all issues on the car by reading and testing rather than asking for help, so this is new. I read about half a billion threads and took a lot of time testing various things, but still having no luck.

I am having an issue with my GTO and was hoping to get some suggestions. See attached for current tune file, config, and log. Prob the best example of the issue I am referring to can be found between frames 2350 and 2500.

Essentially, when I let off the throttle after cruising at 60-70 MPH on the highway, DFCO will kick in and the RPM will drop down to 1100-ish for a moment, then it appears to exit DFCO and RPM will go back up to 15-1600 and hang there. This sort of prevents the car from slowing down much unless you apply the brakes. I can see the timing drop down to 3* or so during the DFCO entry, but then it ramps back to my normal cruise timing of 35-ish*.

I have tried lowering RAF in gear down to about half the desired airflow numbers where the car starts stalling, but it did not affect the RPM hang at all, so I put that back to my normal values. I thought it may be related to Throttle Cracker, so I adjusted those numbers considerably and if you look at the scan log, it shows around 0.035 lb/min during the time of the behavior I am referring to. It is even less than that now as I cut those values in half in the tune file since that log, but that did not make any significant difference.

Wondering if what I really need to be doing is tuning the DFCO exit criteria? Seems like the car should drop to a lower RPM even if DFCO was completely disabled, but that may not be the case.

The car has been tuned for both SD and MAF, but runs in OLMAF mode normally. I do not use closed loop at all. O2 sensors are completely removed except for a PLX wideband.

The car is a 2004 GTO A4
408c.i.
FAST 90
90mm TB
Trickflow 220
239/247 112 cam
1 3/4" Kooks headers
100mm MAF
3600 stall Billet Perfomabuilt converter (somewhat tight for a 3600 really)

Thanks in advance

[gofish7]

Have you tried disabling DFCO and putting values in the rolling idle settings to see if that helps?

[ViaBellator]

I have yes.

I disabled DFCO frequently while dialing in the MAF and VE tables. With DFCO completely disabled, it hangs the same way, but does not have that initial dip in RPM down to idle speed before ramping back up. It just stays up from the time you let off the throttle.

I have tried adding, subtracting, and zeroing out the rolling idle stuff, but it appears to make no difference. In the help file it mentions rolling idle is used in Neutral or with Clutch in on M6 cars, so it may do nothing on the A4 in Drive.

On my way home from work this evening, I adjusted the DFCO exit MAP setting and RPM exit to see if I could get it to sort of stay in DFCO longer, but that just caused a bad dip in RPM and almost caused a stall before surging back up to 1600 RPM or so.

[POWERZONE]

I took a quick glance, some pretty interesting adjustments made to several tables.

I could not see your fueling from your scans, but looking at some other tables, but a quick guess, it looks like you are in PE mode.

Look at your PE TPS% and your PE enable MAP at 15 KPA.

[ViaBellator]

I took a quick glance, some pretty interesting adjustments made to several tables.

I could not see your fueling from your scans, but looking at some other tables, but a quick guess, it looks like you are in PE mode.

Look at your PE TPS% and your PE enable MAP at 15 KPA.

I don't doubt that first statement . I've been tweaking on this thing with HPT for over 10 years now. Through two motors, four cams, multiple transmissions, etc. At this point it runs pretty damn good with the exception of this minor issue and and occasional cold start surge/stall thing.

Fueling is pretty good in 99% of driving conditions. No really rich or lean spikes anywhere in the cruise cells at all. I just used that idle-airflow config because it shows all the idle trim params. Could prob add the WB and scan again if you think its worthwhile. Or just let me know what PIDs you want scanned and I'll create a new config.

Cold PE TPS% under 2000 RPM is still over 36%? I did make an attempt at running in PE at idle a few years ago to still be able to make it run in closed loop at cruise, but it doesn't work on my model year ECM. - Long story, but big cam, big cubes, etc doesn't like to idle without surging unless it is a bit lean in the idle cells and closed loop on narrow bands the thing just wouldn't run. Stayed super rich all the time at idle. Ended up just running full time Open loop.

[POWERZONE]

I have not gone through your tune to see everything that has been done, but it looks like certain things have been changed and to cover these changes, something else was modified. What it is, I do not know.

But looking at your parameters for PE, at frame 1633,1661, those parameters are met. Now how you have set the VE/and MAF to read via lamda is a different story. I would try to set the PE TPS back to stock as well.

But I see the timing drop occuring like at frame 1724 and a few other frames.

Set your DFCO tables back to stock. You have about 3 or 4 tables that have been modified.
See if that fixes the problem.

Something is triggering this to occur around 2000-2300 rpm.

[ViaBellator]

Thanks for the input. I put the PE TPS and DFCO values back to stock along with all of the idle airflow parameters with the exception of RAF and Throttle Cracker and Follower. I drove it to work this morning and seemed to do pretty well for the most part. Cold start was actually much better.

Coastdown was smoother, but still not really what I want to happen. What I mean is: the RPM didn't hang up high, it slowly came down as speed decreased. Pretty much the way it acts when DFCO is disabled. There was no quick RPM drop and no engine braking at all.

The engine helping slow the car down is what I want to happen.

I didn't log it today, but I will on the way home this afternoon.

[ViaBellator]

I scanned the car on my way home Friday and with the stock thresholds set for DFCO, the car does not enter DFCO at all. The MAP values seem to be a bit too high to meet the entrance criteria. MAP is usually around 43-45 when I let off the throttle during cruise and creeps up to 65-70 when the car slows down enough to drop the RPM to idle speeds.

Does anyone have a good rule of thumb for changing the entry and exit MAP and timing for DFCO to account for the higher MAP values a big overlap cam generates?