Need help solving surging deceleration and idle

[Chewy1576]

Hey all,

I recently started over with my 383. I used stock AWSY (Originally AKWH) as a base, then updated for 90# injectors and disabled EGR. I have done one tuning run for the VE table and it probably needs a few more to get it right. It idles pretty smoothly at 700 RPM with IAC counts around 5 when warmed up. The issue I am seeing is that when I let off of the gas pedal and coast, I can feel the engine surging as it's decelerating with the transmission in gear. It's soft but noticeably in 4th and stronger in 3rd. I will go to neutral after 3rd until I come to a stop, then the RPM will drop suddenly, almost die, then come back to normal idle. It has only actually died once, but fired right back up.

I have read that a lean condition during deceleration will cause surging. I have tried changing some of the DFCO parameters to keep from pulling too much fuel or introducing more air but they haven't helped. This morning I disabled DFCO entirely but it still hasn't helped. Does anyone have any other ideas of things to look at to eliminate the surging and smooth out deceleration?

[buddrow]

The surge could be caused by too much spark advance as well as a lean condition. I'm guessing you are using a manual transmission according to the bins you noted. If not, then there is part of the problem.

Buddrow

[Chewy1576]

I guess it would help if I attach my bin and xdf huh? Yes, manual transmission. This morning I burned another chip real quick before leaving for work. I removed 3 degrees of timing and bumped the idle speed up from 700 to 800 RPM. I was using the spark table from the chip that came with the crate engine and it has about 6 degrees of timing added across the table. It seemed to run more smoothly, but I can still feel a little surging when decelerating in 3rd. I will put some more drive time on it today and see how it does.

[Roadknee]

Look in your datalog and see if the surge in engine speed coincides with the O2 sensor switching from rich to lean. Some engines with increased overlap just don't handle lean AFR's at low rpm during coasting or light throttle very well. You'll need to adjust the fuel trim parameters, which start with "O2" in your XDF, to reduce the amount of time the O2 sensor output dwells in the lean position.

[Chewy1576]

You mean these guys?

Attachment 9019

I'm trying to look through some of the other more developed xdf's for comments on what these parameters do exactly. What about the "prop gain" parameters? Would those have an impact in this case?

Here is a log I took when I first created this bin. Only differences between then and now is the decrease in timing and increase in idle RPM I did this morning.

[Roadknee]

Yeah, those are it plus the tables. I've only tuned a few trucks with the 427 PCM and $OD. The parameters are similar to yours, but there are differences. I reached out for help on various message boards without luck. Tuners seem to hold this information pretty close. Maybe you'll have better luck than me.

The surge you're experiencing doesn't look too bad. I've worked with a pretty hot vortec headed 350 that would surge between 1200 and 1500 rpm when the throttle was cracked in Park. Deceleration under 1,800 rpm wasn't much better. You might try reducing the first three cells of the proportional gain table by 33% and blend the next three cells into the upper cells. The end result would look something like this:

9.17
11.78
18.33
25.37
33.99
43.78
56.29
56.29
56.29

You might also reduce the High O2 Limit Slow Filter (scalar) from 851 mv to 800 mv.

These revisions might make it better, worse, or have no affect. Other changes might be needed. I had to experiment with a lot of trial and error to deal with the surge in the 350.