Need help with altitude compensation.

[tech3sandcars]

Can I get someone to look at this MSQ and see if I am doing something wrong with MAP correction? Here is what I have. I do have the system built with 2 map sensors, and can see with tuner studio that both sensors are working. I am doing Alpha-N tuning only. This is a Fuel only computer, no ignition.

I am trying to get the altitude compensation figured out. The first race we went to at 2000 feet I had to readjust the ReqFuel to get it to run right, I realized after the race that the barometric correction was a flat line. I readjusted the line to what I had back-calculated from the adjustment of ReqFuel at the 2000ft race.

So this last weekend we went and raced at 4000 feet and had the exact same issue again. It acted like there was no barametric correction going on. I had to drop the ReqFuel about twice what I did for the 2000ft elevation race.

We are now doing a race that will change in elevation from 2000ft to 7000ft and really need this system dialed.

I did dyno tune this motor at about 500 feet and the mixture was really nice at about 12.8:1 under full power, so I am pretty confident my base tune is really good.

Base tune: ReqFuel: 7.0
2000ft: ReqFuel: 6.6
4000ft: ReqFuel: 6.3

In the MSQ I left the ReqFuel at 6.3 and have not turned it back to the 7.0 yet.

Fallon63 main fuel.msq

(25.95 KiB) Downloaded 58 times

[tech3sandcars]

I see 7 have down loaded my msq, any thoughts yet?

This race we are entering is a 550 mile offroad race that goes from Las Vegas to Reno, I want Microsquirt to be in the front of the pack. This race climbs anywhere from 2000ft to 7000ft in elevation. I have been very happy with the Micro so far and it has been the least of the worries on keeping the car in race form.

I also have a few other thoughts about keeping things in check for changes in altitude, I do have an LC1 that I could use to do AMC but there seems to be scattered information around the forums, maybe someone can direct me to a good thread to look at. Also I do have a ford MAF sensor around that I could try but not sure how they will work with radical camshafts, I have to use Alpha-N because the vacuum signal is really bad, this motor idles at about 80kpa. Maybe MAF/MAP blend would be a good option since my MAP is actually TPS (in pure Alpha-N) and I could use that for the idle area only and use MAF everywhere else.

Any replies and thoughts would be appreciated trying to get this dialed ASAP

[904svo]

Just a WAG, The 2 map sensors have to be same!! It sound like you have mismatch in sensors and the correction won't work right.
PS you only need the MS Map sensor unless you have blown engine ( turbo or blower).

[tech3sandcars]

Thanks for the reply, I built a board with 2 map sensors, one for engine and one for atmosphere, they are both the recommended sensors for the Micro. I can read both the values and see that one in reading manifold (although I am in pure Alpha-N) and one is reading atmosphere. So I think that part is OK, I just don't know if all my settings are correct or if I don't have something turned on. There is the 2 point barometric correction, which is set with the default numbers, and then they is the barometric correction table, which I have modified with a certain slope but does not seem to be making any difference.

[grippo]

I believe the terminology is incorrect in the alphaN menu. You have set pure alphaN and I think that is why baro is not having any effect. Try selecting alphaN blend and setting the rpms so that you are always above or below them. I forget how it goes, but I believe if you set both lo and high rpm to a very high number like 15K, you will effectively have pure alphaN but baro will work.

You have to select the rpms in a menu called "Alpha-N Blending".

[tech3sandcars]

Ahhh wise one, makes sense, I will make adjustment ASAP, thanks

[tech3sandcars]

Tried the recommendation and no worky, The minute I go to the menu and switch to Speed Density/Alpha-N the motor dies, my second MAP sensor reads 99.6 (I am at about 600 ft elevation) so there should be almost no compensation going on according to my "Barometric Correction" table. I have the blending way up at !2 or 13K. as soon as I switch it to pure alpha-N it fires right back up. Here is my msq, maybe someone else can peek and see if there is some other setting messed up. All I am after is to add altitude compensation to my Alpha-N program that works pretty good.

I've looked at the formula from the manual: barocor = baro correction from 2-point table + baro correction from new 6-point delta correction table both corrections should be adding almost zero at my altitude. When the motor dies I cannot get it to start at all until I switch back to alphaN only.

I will try a few things over this weekend and report back, would it be helpful to post a datalog file?

[grippo]

There is a switch that does not show up in the ini file that allows you to use the rpms so that pure alpha is above the max rpm or is below the min rpm, and vice versa on the opposite ends. I need to fix the ini file and the nomenclature, but won't be able to do that until Tuesday. Meanwhile, I believe you can get it to work by setting both rpms to say 10 rpm instead of 15000.

[tech3sandcars]

I had a chance to have a good look over the weekend and looked closely at a few things. I hooked a vacuum hose to the second map sensor and used the mighty lung to suck on the hose to see if there was any affect. Under the Tuning/Real time displays/All channels of Tuner studio I was able to see that there was correction going on. I put the slope in the barrometric correction table steep enough that I could hear the difference in the motor as I sucked and blew on the hose. So I think that is working. I have made the selection under the General tab of tuner studio to use Table for "Prime, Crank PW, & ASE tables" , but when I look in Megatune at the same option they add the Baro Tables to the end of the "Prime, Crank PW, & ASE table" string in the SW. So I am assuming by making the selection to use table it also includes barometric even though it doesn't say so in tunerstudio. Anyways it seems to work on the bench.

In Tunerstudio there is also another selection under "other fuel setup/other fuel settings", there is a drop down under the "VE table adjustments" that asks Fuel/Ign load index adjustments, I have it set for "Use MAP for Baro" is that correct?

I found some information on the internet that states how much HP is lost for changes in elevation, its documented a few times on some recognized sites. If I take that info and change the elevation to KPA and enter that into the table it should get me in the ballpark....thoughts?

And finally this last race we were at where I was explaining that I had to readjust the ReqFuel for the elevation may have been more to correct for the temp and humidity we were at. At race time (4000 ft) it was 103deg. outside and about 10% humidity. I am thinking that maybe I need to do a little more air temperature correction...thoughts? I looked at my table and there was nothing except a flatline there.

[grippo]

I would not use MT for 3.4x code - its not supported and may not work correctly in all cases. I am going to fix the TS ini file and hopefully clear up the confusion.

Using "Adjust MAP for Baro" only affects the index of the VE table. So in your case you have a fuel pulsewidth something like:

Pw = ...... x (alfaN x barocor) x VE(alfaN, rpm) without the option,

and Pw = ...... x (alfaN x barocor) x VE(alfaN x 100 / baro, rpm) with the option.

I have heard conflicting information about which is correct. And when you throw in alfaN it becomes a real mess. What we really want is to measure the mass air and using tps does not directly do that. To do it right requires using special throttle eqs which we have not had time to test. And this has to be compared to MAF which does measure air directly and then determine where, if anywhere, MAF doesn't work and TPS does. Until we can do that we have tried to give enough options so people can try many things. If you have a short time fuse, I would tend to leave the VE index the way you have it and focus on: (1) get the air temp right at a fixed altitude. Use ducting to heat the air or ice to cool it. Once the air temp correction is established, it should be correct at all altitudes.
(2) then build your baro correction table - you can make this anything you want. So yes if you have info on baro correction vs elevation put it in the table. If you are still not satisfied, only then would I fool with the "Adjust MAP for Baro" option.