My Megasquirt adventures over the years
General settings are up next. These extrapolate more on how the calculations will work and include some sensor smoothing options:
I've seen some people get confused with the baro sensor limit settings. These limits are only for the reference air pressure taken when power is first applied to the system, not the values you might see while the engine is running. There are a couple of different ways the MS can handle barometric correction. If you drive in a place where the altitude doesn't change much, initial MAP reading should suit you fine. What happens is when you first turn the key, the MS records the air pressure before the engine is running to use as a reference for all further calculations. This of this like setting an altimeter on a plane based on the local air pressure. If you are driving up a mountain, this could cause some issues because you probably started your car either at the top or the bottom, and the pressure on the other end is likely pretty different. You can run two separate sensors to combat that issue though. One would be installed in the manifold like normal and the other would be left open to measure static air pressure. This lets the system adjust the reference on the fly.
The general sensors section describes how signals get smoothed between the sensors and the MS. Higher values mean less smoothing. Ideally, you'd have all the values at 100 if you have good clean signals with strong connections and no interference. You might smooth some signals just to make them look nicer on gauges though, like coolant temp or stuff like that.
The right side of the page goes into more detail about your control algorithms. This is related to the original selection on the last page, but I believe is slightly different. These settings determine how the y axis for the fuel table and the ignition table are calculated, independent of the actual algorithm that calculates how much fuel to inject. I haven't messed with these, though I could see how it could possibly be useful. The main setting on here is the "incorporate AFR target". The has to do with the fueling equation and setting this to include the AFR target makes tuning a little easier in my book. It will get more apparent once we start looking at tables, but if you don't include the target, you have to build you fuel enrichments into your main VE table. Functionally speaking they will work the same way, but it gets a lot easier to change things later if you keep the enrichments on the AFR table instead of the VE table, plus it makes table switching (more on that later) easier. This is also where the stoichiometric setting comes up again. It's tied to the value from the last page as well, so if you change it on either of these windows it will change the other. It's hard to explain exactly why to leave this at 14.7 vs the 14.4 I talked about before. It's easier if you think in lambda, which normalizes AFR to the fuel in use. In lambda terms, 1.0 is stoichiometric, regardless of the fuel being used. So whether you put methanol or gasoline or rubbing alcohol in the tank, if you are putting in the correct amount of air to burn it all lambda is equal to 1. I believe most O2 sensors actually read lambda natively and then convert that to whatever number you want for the fuel you are using. I am thinking about changing my tune over to read lambda, but haven't taken that plunge yet. My understanding was that the Megasquirt source code had 14.7 built so deeply into the calculations that it was hard to get away from thinking of it as "normal", even if the fuel is slightly different. Maybe that's changed, but I haven't dug into it enough to see for myself yet.
General settings are up next. These extrapolate more on how the calculations will work and include some sensor smoothing options:
I've seen some people get confused with the baro sensor limit settings. These limits are only for the reference air pressure taken when power is first applied to the system, not the values you might see while the engine is running. There are a couple of different ways the MS can handle barometric correction. If you drive in a place where the altitude doesn't change much, initial MAP reading should suit you fine. What happens is when you first turn the key, the MS records the air pressure before the engine is running to use as a reference for all further calculations. This of this like setting an altimeter on a plane based on the local air pressure. If you are driving up a mountain, this could cause some issues because you probably started your car either at the top or the bottom, and the pressure on the other end is likely pretty different. You can run two separate sensors to combat that issue though. One would be installed in the manifold like normal and the other would be left open to measure static air pressure. This lets the system adjust the reference on the fly.
The general sensors section describes how signals get smoothed between the sensors and the MS. Higher values mean less smoothing. Ideally, you'd have all the values at 100 if you have good clean signals with strong connections and no interference. You might smooth some signals just to make them look nicer on gauges though, like coolant temp or stuff like that.
The right side of the page goes into more detail about your control algorithms. This is related to the original selection on the last page, but I believe is slightly different. These settings determine how the y axis for the fuel table and the ignition table are calculated, independent of the actual algorithm that calculates how much fuel to inject. I haven't messed with these, though I could see how it could possibly be useful. The main setting on here is the "incorporate AFR target". The has to do with the fueling equation and setting this to include the AFR target makes tuning a little easier in my book. It will get more apparent once we start looking at tables, but if you don't include the target, you have to build you fuel enrichments into your main VE table. Functionally speaking they will work the same way, but it gets a lot easier to change things later if you keep the enrichments on the AFR table instead of the VE table, plus it makes table switching (more on that later) easier. This is also where the stoichiometric setting comes up again. It's tied to the value from the last page as well, so if you change it on either of these windows it will change the other. It's hard to explain exactly why to leave this at 14.7 vs the 14.4 I talked about before. It's easier if you think in lambda, which normalizes AFR to the fuel in use. In lambda terms, 1.0 is stoichiometric, regardless of the fuel being used. So whether you put methanol or gasoline or rubbing alcohol in the tank, if you are putting in the correct amount of air to burn it all lambda is equal to 1. I believe most O2 sensors actually read lambda natively and then convert that to whatever number you want for the fuel you are using. I am thinking about changing my tune over to read lambda, but haven't taken that plunge yet. My understanding was that the Megasquirt source code had 14.7 built so deeply into the calculations that it was hard to get away from thinking of it as "normal", even if the fuel is slightly different. Maybe that's changed, but I haven't dug into it enough to see for myself yet.