Need help solving surging deceleration and idle

[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.

[Chewy1576]

I will try those changes in the morning. I was also reading this article (http://www.dynamicefi.com/Tune_Intro2.php) about deceleration and it indicated the injector offset may be too low, especially for engines with different injectors or increased fuel pressure. My application has both, as I am running 80# BBC injectors at 18 psi. I modified the BPW for the larger injectors and injector bias according to the values from Dave W's TBI Calculation spreadsheet, but maybe the bias is too low? I also noticed that the battery voltage in the datalog cycles between 13.3 - 13.8 volts indicating the alternator could be on it's last leg. Increasing the bias means I will need to do more work with the VE table, but that needs to be done anyway. I'm also looking at other injector related parameters in a 7.4L manual transmission bin for comparison to see if I may have left anything out. I just have tomorrow to tinker before I leave town for the weekend, so I may not get to it for a few days.

[91dime]

Do you have a wideband o2 hooked up?

Not trying to hijack the thread but im also having similar issues but i have an automatic. I have the 350 injectors running at 20psi on a 5.7L so its a big change from stock and never had the issue before the fuel system overhaul, from what i can remember at least. Now the truck drives and idles fine but on deceleration it acts like DCFO is turned on although iv tried turning it off for testing. At any speed when i let off the throttle, i can feel the fuel shutting off and the wideband confirms that. It starts kicking to max lean, around 22 afr, then back to normal then back to max over and over until i apply throttle then its smooth until i let off again. From what i can see it happens no matter how fast im driving. Even shut off once while slowing down for a light.

[Chewy1576]

Unfortunately, no wideband O2, yet. I was looking at the Innovative Motorsports LC-2 to replace the stock O2 sensor and use the narrowband simulation output to feed the ECM and put in a gauge also, but that will be down the road.

The suggested O2 parameter changes and a few BPW/injector related tweaks have helped with the surging, but it's not completely gone. There are times where it will decelerate while in gear and transition to idle smoothly, and others where it will surge and jerk when getting to idle. My next change will be increasing the injector offset a little bit more, but that will have to wait until next week. I have attached my last data log from today. This one was for VE corrections.