(tried replying to other thread, but 10K character limit.....)
a little reading and i answered my own question about 3 vs 1 MAP sensor. 1 sensor connected to all 3. interesting.
i also read a little bit about how people are using the MAP sensor input to a PC-V (or whatever) to try and make the fuel mapping changes load-referenced vs tps referenced.... trying to think about whether this is a good thing or not. obviously some folks have put a bunch of effort into it and there's interest in it, so i'm going to put down some thoughts and people can feel free to pick it apart or expound on it.....
the main reason to have fuel tables referenced to load (MAP) is because it's pretty accurate way to tell the ECU what the engine needs, vs what the TPS is. say you are lugging up a hill with a lower rpm and a lower TPS for some reason, say 5% TPS..... you have the RPM, you have the TPS, you have the VE by looking up the value, and so the fuel calculation goes. but, the engine is struggling a bunch as the hill is steep and you are being stingy with the throttle. you may be at 60 kpa (i know that the R3 ECU seems to use hPA, but i think in kPA since 100 is about atmospheric, or WOT). if you have a load-based table, you're over in upper 1/2 of the map and probably asking for more fuel in that VE table. in a TPS-based VE table, the ECM doesn't distinguish between 5% throttle at this RPM whether you are going up hill or flat cruise. (obviously, you won't be staying at the 5% throttle uphill and maintaining RPM the same as cruising flat, but whatever). now, in reality what tends to happen is that at lower RPMs going uphill or with a passenger or having a headwind, your load can end up at 100kPA at throttle openings that are *far* below WOT. what i'm trying to get at in perhaps a bit of a roundabout way is that at lower RPMs, you're engine can achieve very high load, and no matter how much you open the throttle beyond that if the RPMs are staying constant (hill gets steeper, wind gets harder, etc) you aren't getting any more air (and thus don't need any more fuel). so, at lower RPMs, MAP is a good thing to use for fueling.
now i'm not a PC-V expert, i stick to flash-based tuning for the most part. piggy-back devices like PC-V work by extending (or cutting off) the pulse-width of the injector based on the internal map it has and the RPM and TPS (or MAP...) inputs. the ECM sends the injector pulse, the PC-V does a lookup based on the other inputs, and either cuts it short or extends it. what it *doesn't* do is make the pulse happen *earlier*.... why is this even a thing you might ask.... depending upon the sophistication of the ECM, it may (should) change it's behavior on injecting fuel timing depending on the operating area that it currently is working in. it's not simply sending injector pulses every other revolution and making them longer as the VE table says to (regardless of whether it's TPS or MAP)..... if it's being smart, it's timing the injection to be at a good time in the cycle as well. recall, the ECM is trying to get the right amount of fuel into the cylinder based on all the table lookups and sensor inputs..... valve timing with poppet valve engines can play havoc on this ideal that the ECM is trying to achieve..... the ECM wants all the fuel that it squirts to be actually in the cylinder when it's time to spark. a few physical things try to prevent that.... 2 of the most obvious are exhaust overlap, where some of the intake charge gets sucked out the exhaust while the exhaust valve is still open, or the piston coming back up the cylinder and pushing some of the intake charge back out the still open intake valve. so, at lower RPMs, when we've got plenty of time to get the fuel in. ex: ~2000rpm, VE = 75% with a 14.5desired AFR and 2.5% TPS in cruise, kPA in the 30s, injector pulse width is say 2.5ms. at 2000rpm, the crank is traveling 30 degrees. with my cams having 246 degrees of intake duration, we've got plenty of time to open and shut the injectors. at low RPM, the ECU wants to inject while the intake is open and the exhaust is closed. at lower RPMs the ECM is concerned with the intake valve opening crankshaft degrees. if it knows when the valve is opening (and they do), it will do a good job of getting most of the fuel into the cylinder. conversely, at higher RPMs you have way less time to inject the fuel. at 8000 rpms, you've got 15ms. (if you're smart, you're keeping the injector's duty cycle under 80%, so you really only have 12ms to get all the fuel in). what (should) end up happening is at higher RPMs, the ECM needs to figure out how early to start the injector pulse to finish when the intake valve closes. intake valve closing is known, so the ECM figures how far back to start the pulse. at high RPMs with appropriately sized injectors, you're spraying onto the back of the closed intake valve in order to get it all in. this begs the question, if you are using a piggyback tuner to extend the intake pulsewidth, at the higher RPMs when the duty cycle is close to 80%, is the injector being held open long enough so that it's now spraying onto the back of the closed intake valve? does it just average out because you've got the leftover fuel sitting in the intake now for the next cycles? when the walls of the intake get wet and puddle from the extra fuel, unless the ECM algorithm is very sophisticated (and the owner hasn't changed the characteristics of the intake system much from the as-designed system), we will have a hard time trying to control the fueling, and probably fairly impossible with a piggyback tuner. you'd probably be best off by making the injectors a bunch larger than necessary and using the piggyback to only shorten the injector pulse.
i sort of forgot where i was going with this, i have to get back to working. anyways, i'm sort of curious how well the MAP-based adjustments to fueling with PC-V are being accomplished with this ECM and isn't it just easier to use the L table instead? the L tables have plenty of granularity it looks like. combined with accurate usage of the F-L switch, i would think it'd be pretty good. maybe i'm just missing the goal of using a MAP referenced fuel adjustment add on.....