Chris, per your previous question all the systems I'm familiar with are capable of running in closed loop. But once they are tuned, you can run them open loop without any trouble, and avoid any questions re the O2 sensor. They all have compensation for air and water temp, altitude via the MAP sensor, etc., whether running in closed loop with the O2 sensor, or open loop where the O2 sensor does not provide A/F feedback to the system.
Jay, I know yours has a great ability to respond to conditions, and how much a system needs to compensate depends on the varying environmental conditions and range of use, but a couple points. This one is long, and generally I don't hang onto anything, but I just feel that there is more to be said about the EFI.
First one is goofy and I am not part of the word police, but just HAVE to say it as a career aviator...your MAP adjusts for
elevation by allowing inputs to calculate air mass. You are fast, but altitude is where your ALL wheels don't touch, I am very impressed with you hanging the hoops, but it's not altitude LOL That being said, all over the net they say MAPs adjust for altitude, but until you call "gear up" it's elevation
Seriously though a MAP measures manifold pressure, and also true, a MAP and BAP are often the same sensor, one with a vacuum source, one sensing atmospheric pressure, but they are quite a bit different in the gonkulation. A MAP, usually combined with an air charge temp sensor (ACT) is used as an input to calculate air mass that is going into the engine in lieu of a combination of measuring it with a MAF (Mass Airflow meter) and a BAP (barometric sensor). You know how yours works, as you said it in your last post
Now, knowing that cylinder fill is a function of relative pressure of an evacuated cylinder, those forces acting upon emptying it more, and those restricting filling it, versus atmospheric pressure trying to push it in, a MAP does technically account for it
mathematically and it is pretty good at sensing engine load differences, but the function is very different than a BAP, and honestly I do not think either MAP or BAP sensors measure very precisely.
Again, how precise is needed? It depends, however, OEM applications do not use MAPs and Speed Density calculations anymore (that I know of), they use MAF and BAP or MAP because they give more exquisite data than the one sensor alone. One reason is the sensors are dedicated to measure one thing (although a lot of new MAFs also measure air temp too, older ones like mine use a separate air charge temp sensor), another reason that EOM shifted from MAP in many applications, is that MAPs are fed by a relatively violent source (think Kaase's clear intake manifold test).
Now, that doesn't mean MAPs are bad or obsolete, they are still used with MAF, the line to the BAP will of course dampen the signal and the BAP itself has some mechanical damping and the ECM has smoothing in the program, but it is by no means a precise sensor IMHO. One thing the MAP does do better than a BAP is measure actually changes in load though, especially when compared against the TPS data with changes in throttle, however, it is used with the temp sensors to calculate changes in air mass where a MAF measures changes in airflow and compares to air temp and baro to come up with the data.
I have seen guys add a BAP to a SD system, so it measures baro and still uses intake pressure from the MAP to have a more precise air density calculation, but I would be surprised if it changes in use much other than adding difficulty to the programming and tuning. It's an attempt to be more reactive though when calculating adjustments.
You and I may never agree, but looking at our complete systems:
My MAF, BAP, and ACT measure all the characteristics of the air coming in, the ECT adds engine temp info, the TPS translates what the guy behind the wheel is doing, then O2 senses what is coming out. All of those provide near-real-time info to adjust well calibrated tables and adjust them within the limits the guy tuning it (or the ECM) allows.
In a SD system like yours, you have a MAP and ACT that provide input to calculate air density, the ECT provides engine temp, and the TPS translates what the guy behind the wheel is doing, all of that is compared to well calibrated and well thought out tables (as you pointed out) but in open loop, you only adjust for changes in
inputs, you don't measure
output when you exclude the O2 sensor info. To me, that is cheating the decision maker by not providing the whole story (
stay with me though, because I actually think for you, it is a smart choice)
I cannot explain your O2 sensor calibration changes and failures, FYI, Brent says he sees some similar things on the dyno, and I cannot say for your application and your environment that your system does not compensate enough,
because it clearly DOES for you and many other guys. You are essentially taking a very precise program and still allowing it to compensate it for many things that a carburetor would have to use physical airflow and fluid/aerosol management (bleeds, boosters, orifice sizes, throttle blades, venturi designs etc) to manage.
Your stuff is WAY more adjustable than that, likely significantly more responsive to environmental changes than a carb, and way cool as you knowHowever, measuring both sides of a process and providing information by design allows more information, and if the sensors on both sides of the process measure more and rely on less calculation, there are less chances for errors. That is true in any human or non-human decision making process, including the ones you ask an ECM to make
It comes down to is where I started, I am not saying open loop is wrong, as a metaphor...how much information do you need to order a pizza vs a big investment decision?
Although there is no way I can ever agree that an EFI without an output loop has as much data and therefore as much ability to respond as one with one, I am not asking or recommending you change
yours, because it clearly is responsive enough for your conditions. How do we know? You are measuring output using your eyeballs on plugs, your O2 sensor during testing and are not burning up pistons.
Additionally, another reason I wouldn't recommend you go closed loop at WOT (even with a very narrow learning factor) is because your environmental conditions change less than the risk you are seeing with a bad O2 sensor. If the O2 sensor fails at WOT you could hurt your car, if it fails cruising around town at drag week, probably not, but my position is, in my tuning, I go open loop at WOT in many tunes, just not in all conditions
Therefore I cannot argue with your technique,
I think it is SMART. However, I just have to stand by my guns that you have chosen to limit the information to your ECM (for good reason) and therefore our academic discussion about ability to respond I still hold my position. You have good reason, but you took an output sensor out of the loop.
Similarly, I think that the setup I have,
for the use of my car and a bunch of street cars out there, is clearly proven by my experiences
and the way modern cars have evolved for precise emissions (read: a/f and timing) control, but again, we use our vehicles very differently and I do not think that the wide range of fuels, elevation, driving conditions, part throttle load, etc, that open loop would provide an ECM used like mine enough data.
One last comment to everyone, Speed Density systems have come a VERY long way, and I think the modern versions like Jay uses, as opposed to 90's OEM, are very good for street use, and I am very happy with the TB systems I have installed using Speed Density (aside from a lack of good interface on most) In fact, SD solves some packaging issues that MAF systems have, and MAF systems are very tough to build, but I generally tune both MAF and SD systems for closed loop where I can, and open loop only when the engine or risk won't let me ( so far...only idle with too much cam/not enough vacuum or WOT).
Again, there is a gradient on how adjustable and then how responsive a system needs to be, and it is a combination of risk/reward and environmental conditions that determine that. Like I said, I do not need a financial prospectus to order a pizza, or even to go out for a night on the town, but as the environment gets more complicated, mo' info is mo' better to be able to respond to varying environmental, load, and fuel changes IMHO and I want that O2 sensor to provide that data at the times I want it to
