Is it impossible to run a type IV in closed loop?, Megasquirt Options

[DNHunt]

After about a month of tuning I have a fueling map that seems close. Most of the map yields air fuel ratios of about 13.8. From what I have read this is about where the motor was designed to run and it runs very well.

However, I continue to have problems with overrun. Between 2600 and 3600 rpms under very light load the air fuel ratio is much richer. This is quite disappointing as I would hope to gain some economy here. The solution would seem to be closed loop with the oxygen sensor leaning out the air fuel mix. The problem is that the pulse widths are so short that O2 correction leads to large changes percentage wise in pulsewidth and fuel mix and the car bucks. I have one more idea to try. I am waiting on some new injectors since it feels as if one cylinder goes dry.

If that doesn't help, it appears to be run open loop and send fuel ou the exhaust or run closed loop and suffer some loss of smoothness.

I'd appreciate any advice,

Dave

[DNHunt]

Mark and Ben

Thanks for the help

I do have the closed loop set to turn off at 1200 rpms and it is hard coded to turn off above 5000 rpms There is no adjustment governed by MAP I am aware of in Megasquirt.

The pulsewidths in the area I am having trouble with are 2.3 to 2.5 ms (1.0 ms of this is a constant applied to the whole map they call openning time.) 2.5 ms is too rich ( about 12 afr) and 2.3 ms is too lean (about 17 afr). I realize that as pulsewidths get shorter each ms chage in pilsewidth will cause a larger charge in afr, but this amount seems too large to me. That has led me to suspect a bad injector ( maybe it is openning very slowly) causing a cylinder to drop out. It seems it is worse when the car is warm.

I was having this same problem with the D-jet prior to converting so I doubt it is the ECU or software. I already replaced one injector and this helped some.

At any rate I'm getting a little frustrated. I want to do this right, I really believe in the megasquirt system, but I'm not sure I have the expertise to get it done.

Dave