The recent MAP as related to Throttle Position thread got me thinking about something and I figured it might make for some interesting pondering (and/or help me understand better) why folks claim that using the MAP signal is a better way to signal how much load is upon an engine. Hear me out...

I guess you could say I'm a ThunderMax fanboi. Actually, I understand Tmax's TPS vs RPM IS one way of tuning, but I also understand those tuning H-Ds have been using MAP for fueling and timing for years. I figured that would be a good way to bring out information and delve into the "whys" of each form of tuning for load. It's a given that MAP is a great tool for quantifying load. But, is TPS vs RPM that far behind? Think of it this way.

When tuning for TPS vs RPM, it's obvious that the throttle setting is the key factor, which is then potentially "adjusted" as the RPM changes. It's safe to assume that if there is less load on the engine and the throttle position doesn't change, then RPM will increase, right? Conversely, RPM drops as you start to head up a hill (higher engine load), right?

If this is true in both situations, then adjusting the fuel or timing at the same throttle setting for higher or lower RPM would have the same affect as adjusting for higher or lower MAP, right? Now, I understand that most folks increase throttle when going up hill, but for the sake of not introducing another variable, I'd like to focus just on a steady throttle setting for now, if possible.

Has anyone thought about this. It doesn't keep me up at night, but I do try to better understand things. Thanks for any input you might have. I want to learn, not start an argument. Let's discuss.
Thanks!

 

well, a big factor is EPA
honda used the tps/preprogrammed injection system and it was flawless with very rare failure, just went through a vt750 for a guy. they eventually added a map to the system. there are soooo many factors that effect an engine that a tps system alone cannot compensate for. you say up/down inclines but what about elevations like mountains? the ole cv carbs could compensate for minor adjustments but there are timing lead requirements that must go with it, hence the map.
what about gearing, 3k in 3rd is a big diff 3k in 5th. now factor in road, ambient and fuel selections, a computer with map can make many decisions a second, a tps not so much. can you use other things like a mass air flow, well yep but more complicated and for to fail. a pressure sensor is way more responsive than a heated wire mass flow sensor and to boot easier to troubleshoot.
even the very old mechanical systems were like map. you had a base mechanical set timing and a pressure controlled aux which pulled back timing as load increased to prevent detonation and such. so nothing new under the sun.

 

@bustert I had thought about elevations. I mentioned the ThunderMax, which of course has oxygen sensors. I figured the O2 sensor would adjust fuel for the thinner air. Timing is a different issue. No "spark sensor" for that one.

Also, your point of which gear you are in is well taken. Would definitely change the amount of load, even at a set RPM. Good stuff! Thanks!

 

I went to a Thunderheart class a number of years ago and the guys there said that the use the map sensor to estimate fuel corrections. I expect that they take the measurement some time when both valves are closed and the TPS is open.. They were kind of vague on the details but I suspect that it works. I've ridden to the top of Mt Evans and Pikes Peak with my 07 EGC and a Tmax. Bike ran fine. It actually got better gas mileage..

The use of map sensor definitely helps with mileage and emissions. It's the reason why HD switched from Magneti Marelli to Delphi.. The MM EFI was open loop Alpha-N.

 

For fuel delivery calculation Thundermax uses an on-board baro sensor that's incorporated into the ECU

 

That's good to know!

 

@fuelmoto you guy’s really need to open a Southwest location!!😎👍🏻

 

The most simple answer is that MAP is a much more accurate way of measuring the load on an engine. When using TPS you get the same answer when holding a steady TPS setting regardless of anything else happening. So think about riding down the highway at a steady TPS on flat ground. Using TPS you get one answer to load and using MAP you many many different ones and the engine changes. Riding at say 20% TPS gets you 20% TPS period. Now looking at a properly setup MAP sensor as you go slightly down hill area the MAP will change or silghtly up hill the MAP will change or on flat ground yet another reading. So all in all, using a MAP sensor is much better for getting a properly running engine in more conditions. While using TPS was one of the original ways of doing it, and was named Alpha-N tuning method, it was replace by MAP based systems in the automotive field back in the late 1970's

 

In the 70s! Don't feel so sohifsticated now!

Thanks for the insight @Steve Cole. As I mentioned in the first post, I've thought about it a few times, and your, and @bustert's responses have helped me think about scenarios I hadn't considered before. Good stuff! Thanks!

 

MAP is pressure. 0 MAP is 0 pressure. 100 MAP is atmospheric pressure which is approx 14.5 psi. A cylinder can't fully fill and achieve its maximum VE potential if the throttle is partially closed and there is only say 50 kpa of pressure or approx 7 psi in the intake. Obviously there is more to it then that but thats the general idea. Diesels are a different story as they don't throttle the air. Nor do they tune for AFR. But that's not a discussion for here. Anyways The ECU uses the ideal gas law to calculate fuel requirements at any given moment in time. MAP is one of those variables. The ECU needs to calculate VE before it calculates fuel. It starts with number given in the VE table and modifies that value according to a set of variables or multipliers. Air intake temp, Engine temp, Engine speed and MAP being major players. The easiest way to understand it is high MAP = high pressure. High pressure = better cylinder fill, Low MAP is less pressure so less cylinder fill with everything else being equal. And if 14.5 psi isn't enough there is always forced induction. In which case you should be tuning with MAP and not TPS. That's as simple as i can make it. The problem with TPS based VE tables is that there is no correction for engine load. It assumes that if the VE is say 80 percent at 1500 RPM with 15 percent throttle, then that's the fuel you get with no correction for load in the equation. Correction does occur after the fact with the 02 sensor, but only if you are in the closed loop portion of the fuel map. Thundermax uses widebands so you get the bigger closed loop window for correction. The Cats clean up the rest. Well that's the theory anyways. A 4 gas machine will say differently. But obviously TPS VE tables do a good enough job to meet current EPA requirements on a Harley V Twin. Would you notice a difference in performance or fuel mileage with a MAP based tune ? Probably not. Its just that MAP is the only way the ecm can determine load under all conditions. TPS just can't do that. All that being said, even though most of us only get TPS based VE tables to work with, Im not convinced the Delphi ECU completely ignores MAP for fuel delivery. I say that because MAP is a variable required by that magic ideal gas law equation. But getting that information is near impossible even though there are at least two guys on this thread that would likely know.