TheDarkSideOfWill wrote:
mk e wrote:
MS does somehting weird. If you don't add the baro sensor it goes way lean driving up a mountain and they all thing thats normal. but it you stop and reset the mixture becomes normal again. The only thing I can thing is they sample baro at startup and are doing a MAP/baro thing somewhere in the math....so adding a real baro fixes the issue. So they might already have a stable load calc. Just guessing though.
I don't see why it would get lean going up the mountain. A WOT with 10 psi of ambient pressure, it should need exactly the same fuel/ignition as it did with 10 psi of MAP at part throttle at seal level. Unless you want to richen the mixture to get a couple more ponies to pull up the grade.
GM uses the MAP to sample baro at key on (IE, does NOT have a baro sensor) before the engine starts turning, but also has PE mode and apparently better baro/load compensation than MS does.
Well....yes and no.
Setting aside the concept of the PE mode for the moment and just doing MAP load sensing as you cruise at constant load up a mountain will need more and more throttle to maintain constant power and stay at the same point in the load. So that's the yes part, the mixture should stay constant just like it does on every other ECU.
The no part is if you are at WOT you can't maintain constant power....but you want to. What the ECU see is the MAP reading dropping which it reads as decreasing load and goes to the fuel/spark for the lighter load. If you tuned your whole map for the same mixture its no problem but normally at lower loads a leaner mixture is used because at lower loads (part throttle at sea level) you aren't trying to make all the power you possibly can. So as you go up the hill you get the mixture gets a bit leaner and you give away some hp. This can be a pretty big problem is the engine only pulls a few inches of vacuum at best anyway because now WOT could get you basically idle timing and mixture. WRONG!
This doesn't happen when you use TPS load sensing.....WOT tells the ECU you want the full power mixture and then it's corrected for the baro where you happen to be. perfect! but you need to tune pretty much every single cell in the fuel and spark tables you can't just do some and linearize things because they won't be linear.
MS though seems to do something different. i think they use a normalized load that is MAP/baro and that solves the load % varies with baro issue, but in the cheapest setup they use MAP at key on for the baro value which is a worthless scheme is you are driving on a mountain. So most add a baro sensor I'm told and have no further problem.
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