One MAF sensor per engine or one per throttle body?

[Flexifueler]

I'm investigating running MegaSquirt on my motorcycle (KTM SuperDuke, i.e. 75° v-twin) and for various reasons, the alternative that seems most appealing to me is running MAF exclusively, together with wideband oxygen sensors. This particular motorcycle has an, as it stands from the factory, indenpendent control of each cylinder, i.e. sequential ignition and fuel injection with one oxygen sensor per cylinder. As far as I can tell from the documentation, there's only one input for a MAF sensor on any of the MegaSquirt variants. However, to be able to adjust each cylinder optimally, wouldn't I need one MAF sensor for each cylinder/throttle body?

[grippo]

The single MAF + O2 sensor per cylinder would be a good way to go if there were an ecu that could handle it. But single MAFs are in the minority in the aftermarket, and dual MAFs would be extremely rare. If it were me, I would run both MAFs but add their signals together to produce a 0-5V signal whose flow was scaled so the sum of the two signals was 5V at max flow. This could easily be done with a PIC processor and probably even easier with a summer + 50% voltage divider circuit. The assumption would be that there is nothing significantly different between the 2 cylinders, so they should flow approximately the same. I don't think you would see much difference between the two and with a microsquirt and v3.x code you can get individual fuel and spark trims for each cylinder.

[Flexifueler]

Thanks for a quick reply (and apologies for not following up sooner).

I'm not sure if I understand this correctly but what you're saying is that automatic O2 adjustment (i.e. closed mode) is not available when using MAFs? It of course makes senses, since I did see that AMC is disable when using MAF-Only, just didn't connect that for some reason.

Thing is, I plan on using MegaSquirt (well, MicroSquirt ideally) for a flexifuel system but running fixed maps, even though I suppose I can switch between an alcohol and a gasoline map using the flexifuel sensor. The issue would be the mixed fuel scenario when I run a blend of gas or e85. Was trying to avoid messing with VE tables by using MAF but I suppose the only option is Automatic Mixture Control and MAP-Only really. Is there a technical reason for not being able to use AMC with MAF or simply a lack of demand for such a feature?

I suppose the ideal ECU would be a MAF+AMC (WB O2) while also having the possibility to select maps based on lambda correction (i.e. when lambda correction is more than a certain percentage for a certain time, it switches to the other map). That's how most flexifuel cars do it, as far as I know. It would elmiminate one fault point, apart from the fact that the GM flexifuel sensor is both expensive and hard to find here in Sweden. I realize that my needs are a bit exotic compared to the majority of your customers though.

[grippo]

What I meant was 1 MAF + 1 O2 per cylinder (total 2 MAF, 2 O2s) would be a good system, but none of the MSs can handle the 2 MAFs, but all the MS2s handle 1 MAF and 2 O2s and they all handle closed loop with MAF or no MAF. The AMC uses closed loop O2 to adjust the VE table, but when you have MAF you don't use the VE table. You can turn AMC on and I believe it will update VE, but the VE won't be used. However, this is something that could easily be changed in the code if there was a need for it. You could initially set VE to all 100s (no correction) and then let AMC fine tune it.

As far as flexfuel, yes it does require the sensor to do it right, but I believe the extra code has a dual table option that can be switched for different fuel. I don't know if it does it automatically as the egocor correction becomes large for a long enough time.