7427 very rich deceleration problem

[Daveo91]

My VE tables are looking pretty good these days and truck is running (seat of the pants) awesome. But I have a very rich condition in deceleration, foot off the gas, TPS=0. I've spent a lot of time playing around with both VE tables. I thought I had it figured out when I finally realized as soon as I took my foot of the gas it was going into the idle VE table, but that turned out to be not the problem.

Today I spent some quality time in Excel with a data log that I took last night. Filtered to all rows where speed > 3 mph and TPS = 0. Most rows WB is 12.5 or lower, bottoming out in the high 10s. The vast majority of those rows BPW = 0.488, which happens to be the same value as the scalar, "Minimum Synchronous BPW." There also is "Minimum Synchronous BPW Allowed" with the same value set. So it appears I'm being limited in most (not all) decel situations by that value. Can I just change it to a lower number? Should I change it in both? The XDF description for the allowed scalar is "Minimum synchronous BPW allowed if PCM calculations are less than setting." This begs a question, I am not seeing calculated BPW as one of the available outputs when I export. Is there a way I can output that (maybe it's called something else) or can I calculate it myself?

[brian617]

Some things to think about,

If you go back to the carbureted era you would remember that when you chop the throttle on decel the mixture is going to be very rich, high vacuum and closed throttle plates.

Leaning out the mixture or even cutting fuel completely, decel enleanment, causes high engine braking.

The moment you step back on the throttle the extra fuel in the manifold might help the transition without having the mess with AE too much.

With my 7427 and Manual transmission decel enleanment is very noticeable. I can feel and hear the change when the injectors quit pulsing.

[Daveo91]

Some things to think about,

If you go back to the carbureted era you would remember that when you chop the throttle on decel the mixture is going to be very rich, high vacuum and closed throttle plates.

Leaning out the mixture or even cutting fuel completely, decel enleanment, causes high engine braking.

The moment you step back on the throttle the extra fuel in the manifold might help the transition without having the mess with AE too much.

With my 7427 and Manual transmission decel enleanment is very noticeable. I can feel and hear the change when the injectors quit pulsing.

Thanks - agreed that I do not want to swing things too far that would create a lean condition when I step back on the gas. But it will sit there and hang out at 10.9-11.1 or so continuously even on long decel events. Note that the conditions I am speaking of do not involve DFCO since they are outside of the parameters that allow it. DFCO is working fine from what I can tell. I'm mostly concerned about in-town driving where RPM is not high enough to allow DFCO. Also not talking about decel enleanment. AFAIK that is only triggered when TPS is decreasing, but still greater than zero?

I have been playing with those limits a little and I'm still pretty rich on decel, but it will lean out to the 12s or even 13s as the decel event continues. Seem to be on the right track. I'm at 425 minimum BPW now and will probably not go much lower than that. I have not noticed anything amiss when acceleration starts back up. One thing I discovered is to keep the two values the same (minimum value and minimum allowed value). I'm not sure why both are there, but when the allowed value was lower than the other one, things went a little wonky on decel with TPS greater than zero (foot still on the gas). In certain conditions I would get a surge with lean/rich swings. Keeping both scalars at the same value seems to resolve that.