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]

Open loop means the fuel injection ECU does not use an oxygen sensor to correct the fuel mixture. Closed loop uses this correction. Most modern fuel injection systems use closed loop to correct to stoich ~ 14.7 parts air to fuel which burns all the fuel and yields few emissions. The catalytic converters require this to be very close.

I would like to run most of the time at ~ 13.8 afr since our air cooled engines need to run rich. Under acceleration I would like to see about 12.5 or so for max power. This replicates at least to some extent what the stock D-Jet does. The challenge is that this requires a system that allows the target air fuel mixture to vary. The firmware I am trying to use allows the mixture to vary with load (manifold vacuum) so I hope to have a 914 running closed loop with variable afr (more or less a modern D-jet) that can accept almost any engine change I would throw at it with little tuning.

Dave