Rich swing on deceleration
 

I've been having an issue with my tune and I'm not sure what's causing it. Anytime I lift off throttle to decelerate the car will go full lean for a little over a second, it then swings to full-off-the-wideband rich for a second, then goes back to lean.

https://www.miataturbo.net/attachmen...ichoverrun.png

I've messed with settings in overrun fuel cut without affecting it. The bottom VE table row is super low as is the Target AFR table, and EGO Correction doesn't seem to be making changes. Just not sure what else could be making it dump fuel at such a random time. Any suggestions are appreciated. Log and Tune attached if anyone feels like digging through my mess (using VE and Spark table 3, currently on E85).

maybe at first it goes lean due to your lean over-run cells and then proceeds to swing to rich because it sucks fuel from the intake manifold walls?

Thanks for the reply. I found that the rich dip is occurring right when my IAC opens (set to remain closed for 1 second during shifting) so it sounds like you may be on to something. Is that a normal thing or is there something I can adjust to fix it? I don't remember this happening before or on any other cars/ecus, but maybe I just never noticed.

It looks like the IAC is set to remain closed above 1800rpms for 1 second. I don't really see why you would need the IAC open above 1800rpms so I'm going to try changing it to 15 sec and see if that fixes the problem.

Doesn't look like the IAC was the issue. It's still pegging full rich for about a second on decel with the IAC closed.

AE and EAE is what's causing it I bet
double check both, if you accidentally put in a positive value mid-range of AE decel it will do what you're describing exactly

I don't see PW or injector duty going up at that time, so the ECU isn't commanding more fuel, maybe Eunos91 is right with the manifold walls. It doesn't look like Decel Fuel Cut turns on either, is that configured?

18 and I have fought this kind of thing pretty hard. These are my present thoughts:

Think about what is happening. Slam the throttle closed, almost no air in the manifold. No control. Any tiny change in fuel is going to effect AFR massively. You are also in a horrible range of even the best injectors, so imperfections in temperature, dead times, low pulse non-linearity will haunt you.

Also, there is little flow going to the O2 sensor, so all kind of time delays come into play making evaluation pretty hard.

In the end, you are asking exactly ZERO power output from the engine, and the duration of these events are short.

This is a time to look the other way.

OTOH, 18 is correct that the fluctuation can be reduced by perfect EAE, or no EAE (no EAE will go really rich, but no fluctuation). However, as stated above, you would likely chase this forever (it is good today, bad tomorrow) and IT DOES NOT MATTER.

Here's a pretty good throttle drop from yesterday... the last one shown (no special actions on my part, this is my tune): Note that it only went 10.3 rich and 16 lean. But most importantly, it goes right on back to proper almost immediately (less than a second).


https://cimg4.ibsrv.net/gimg/www.mia...8f6172323d.png

But you see, the one before it was a little more dramatic. And if you look at the bottom graph, you can see what EAE was doing to try to control things.

Thanks for the replies. I'll go back and check over AE and injector settings to see if anything look suspicious. I figured it wasn't particularly hurting anything, just annoys me to see it doing that. I do feel better that I'm not the only one seeing this kind of thing.

I thought for sure it was turned on, but looking at the tune it is disabled. I'll turn it back on and see what happens. Thanks.

Actually, this is a softer let-off, more like what you are talking about. You can see only a slight going rich, then 18 lean, then fuel cut comes in. So, yeah the rich swing should be able to mostly be tuned out with AE / EAE, but over-run areas of VE do not stay consistent for me. And I presume for most people as it is common wisdom to not let VEAL mess with those cells.


https://cimg0.ibsrv.net/gimg/www.mia...b0e4d67bee.png

Now I'll go back to work and stop bothering you.