Baro fuel calculation

Testing and development of Megasquirt 3

Moderators: jsmcortina, muythaibxr

suberimakuri
Master MS/Extra'er
Posts: 632
Joined: Sun May 02, 2004 2:16 pm
Location: Auckland, NZ
Contact:

Re: Baro fuel calculation

Post by suberimakuri »

You're running percent baro.
So you're not getting fuel reduction due to change in ve table.
Thus your baro correction table will be different to speed density users.
Ie at 70kpa elevation pressure, instead of using 70kpa row for WOT (SD) you will be using your 100 row.

Nothing sinister. I personally think both approaches work.
TheSilverBuick
Experienced MS/Extra'er
Posts: 356
Joined: Thu Feb 02, 2012 9:08 am

Re: Baro fuel calculation

Post by TheSilverBuick »

I run %Baro now because after two years of running speed density and having my tune all jacked up every time I drove off the mountain I switched to something that worked and maintained my AFR's where I wanted them.
"Hey, at least the Skylark proves that even a messy hack can patch together a reliable EFI system. I can't think of a time the MegaSquirt has left me stranded since installation ~100,000 miles ago."

Drag Week 2011, 2012 & 2015. - BB N/A - 1977 Skylark w/Buick 455 EFI and TKO-600!
jsmcortina
Site Admin
Posts: 39585
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK
Contact:

Re: Baro fuel calculation

Post by jsmcortina »

Back to my original point though - I believe that the calculation was previously dubious due to the * 100/baro that was built-in. So all other baro tuning would have been working around that.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
TheSilverBuick
Experienced MS/Extra'er
Posts: 356
Joined: Thu Feb 02, 2012 9:08 am

Re: Baro fuel calculation

Post by TheSilverBuick »

jsmcortina wrote:Back to my original point though - I believe that the calculation was previously dubious due to the * 100/baro that was built-in. So all other baro tuning would have been working around that.

James
As dubious as the equation may look or be, when I move these dots up or down at different barometric pressures (from 64kPa to 103kPa) the AFR adjusts accordingly, with no other changes. Something in the programming is right, rather the scale is off or not as I mentioned (maybe 30% variances go to 10% variances with the new coding) is something different but has been easily tuned around so it functions correctly.

Image
"Hey, at least the Skylark proves that even a messy hack can patch together a reliable EFI system. I can't think of a time the MegaSquirt has left me stranded since installation ~100,000 miles ago."

Drag Week 2011, 2012 & 2015. - BB N/A - 1977 Skylark w/Buick 455 EFI and TKO-600!
jsmcortina
Site Admin
Posts: 39585
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK
Contact:

Re: Baro fuel calculation

Post by jsmcortina »

I put your numbers into the spreadsheet I had for the 100/baro effect and what it looks like you are really getting is:
65kPa = +20% fuel
75kPa = +9% fuel
94kPa = +0% fuel

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
TheSilverBuick
Experienced MS/Extra'er
Posts: 356
Joined: Thu Feb 02, 2012 9:08 am

Re: Baro fuel calculation

Post by TheSilverBuick »

Because I live and tune at 80kPa atmospheric pressure, it will probably look like -10% to +10% from my base tune, which sounds reasonable :D
"Hey, at least the Skylark proves that even a messy hack can patch together a reliable EFI system. I can't think of a time the MegaSquirt has left me stranded since installation ~100,000 miles ago."

Drag Week 2011, 2012 & 2015. - BB N/A - 1977 Skylark w/Buick 455 EFI and TKO-600!
Nightstalker1993
Helpful MS/Extra'er
Posts: 75
Joined: Tue Jun 03, 2014 11:09 am

Re: Baro fuel calculation

Post by Nightstalker1993 »

TheSilverBuick wrote:What do airplane pilots do? They manually lean the mixture out as they go up because the engines start to run richer, despite fixed throttle position and rpm..
http://flighttraining.aopa.org/students ... xture.html

Holley recommends going down 1 jet size for every 2,000 feet of elevation gain because it starts to run rich....

Bonneville racers tuning at sea level have to pull upwards 15% of their fueling when they get to the higher elevations of Bonneville.
http://www.speedtalk.com/forum/viewtopi ... 9&start=15

There are dozens of similar examples and experiences like the above with simple google searches, everything from motorcycles, to miata's, to landspeed and drag racing.

Here is an old screen shot of one of my car's baro table, and they all have the same general shape. Fuel subtracted with elevation gain and added with elevation loss and my AFR's stay in the same place without EGO correction turned on.


You can disagree, but some solid examples other than a web page citing a sketchy test that probably caused the goof in the megasquirt calculation and why my corrections are over 30%, and with the new calculation will probably drop to a more sensible number, but until I take the time to re-tune with the new calculation, I won't have an answer to that.
Leaning out when elevation increases applies to carbs or alpha-n strategies as the airflow pulling the fuel out would be the same, but the density of the air is lesser thus lesser mass. If in our case we are already running speed density which measures the pressure in the manifold directly and directly affected by barometric pressure. If on an NA engine, you go WOT at an elevation with 70kpa barometric pressure, your MAP will read 70kpa and will base all it's calculations on 70kpa MAP and so the reduction in airflow is already calculated in that. What barometric pressure affects is the pressure at the exhaust which affects the engine VE and due to reduced pressure in the exhaust, VE will go up, thus requiring the addition of fuel. Curious though, is your vehicle NA or boosted? Mine's boosted.

http://www.efi101.com/forum/viewtopic.p ... highlight=
At 8000 ft / 75 kpa Baro and full throttle the MAP is 75 kpa and the Atmospheric pressure resisting the exhaust flow is 75kpa.

At sea level and 75 kpa MAP (discounting VE loss for the partial throttle closure to achieve 75 kpa) the Atmospheric pressure resisting the exhaust flow is around 100kpa.

For the same MAP (Manifold Absolute Pressure) the 8000 ft engine has less atmospheric pressure resisting the exhaust flow. So even if the sea level engine had a restrictor to limit the MAP to 75 kpa at full throttle the atmospheric backpressure on the exhaust will result in a lower VE than the 8000 ft engine.

I have dynoed an engine at sea level and then checked it in Leon, Mexico for the WRC round (at both Leon and the highest stage altitudes). I tried the ignition timing with MAP only and then MAP corrected with Baro. Without Baro correcting the Load higher than the MAP the engine would ping (detonate) at manifold pressures that had been no problem at sea level.
I can confirm that my map based engine was tuned (without barometric compensation) at 800m (2625ft) above sea level and when driving back to sea level the engine was clearly running richer.
Car was running on a HKS Fcon Vpro ecu at that time.
Hi Turboivo

Volumetric Efficiency of a motor increases with increasing altitudes.
With higher altitudes there is less back pressure in the exhaust resulting in a higher VE.

Regards,
Henk
__________
http://www.motec.com/forum/viewtopic.php?f=11&t=170
Paul
In the case of MAP sensing you would do MAP/BARO for effcy right? In the case of MAP sensing in theory for a given engine speed and manifold pressure the fuel requirement is the same so there should be no need for a barometric compensation. BUT barometric air pressure may have an effect on the VE of the engine because if its effect on the exhaust as you and Martin have pointed out. If the VE of the engine changes the fuelling requirement will also change. You could use a barometric sensor to compensate for this but the values in the table would not be as per a normal barometric compensation.

And lastly, before I installed my 2nd map sensor, I personally encountered lean-out as altitudes climb until my AFR safety system kicked in, The mountain road I climb up, drops to a baro of around 80kpa but noticeable lean-out happens before even reaching 90kpa baro.
savagerocco
Master MS/Extra'er
Posts: 756
Joined: Thu Oct 20, 2005 11:09 am
Location: Ogden UT USA
Contact:

Re: Baro fuel calculation

Post by savagerocco »

What would decent real world settings look like on the baro correction screen? I live about 4500 in altitude and have baro pressure around 86.4 most days. I do go to higher and lower altitudes fairly regularly.
Last edited by savagerocco on Mon May 11, 2015 3:25 pm, edited 1 time in total.
Brent Savage
life behind the zion curtain
90 audi RS2 20VTQ 6sp MS3, MSX COP and Sequential and now MAF
87 Scirocco 2.0 ABA 16v EIP tubular cast MSII COP
86 Audi 4K20VTQ MSII
90 Audi 90 sedan 3.6l DOHC V8TT (project car)
89 VW cabbie (bitch basket) 2.0 ABA Turbo MSII
TheSilverBuick
Experienced MS/Extra'er
Posts: 356
Joined: Thu Feb 02, 2012 9:08 am

Re: Baro fuel calculation

Post by TheSilverBuick »

Okay, baro correction calculation aside. What are your pulsewidth values doing at a fixed 80kPa, fixed RPM and fixed AFR but at 6,500ft elevation, 2,500ft elevation and at sea level? I watch my PW's go up as I go down in elevation.

I spent two years chasing this problem. Tuning WOT here at 80kPa was good and well, solid 12.5-13 AFR's, then I'd rattle the engine at part throttle climbing a dinky hill around sea level because it's so leaned out, and timing was set conservatively around 30º for WOT power at 80kPa, and was still at a conservative 30º at part throttle at 80kPa at sea level (that's why I've left my timing table as speed density). I'd richen it up to get it to stop rattling, and when I got back home WOT would be stupid rich in the 11's. Got to the point I had the "California coast" tune and the "Home" tune queued up in the laptop and switch them over in Las Vegas at 2,500ft. Same cells on the VE table, different AFR results.
"Hey, at least the Skylark proves that even a messy hack can patch together a reliable EFI system. I can't think of a time the MegaSquirt has left me stranded since installation ~100,000 miles ago."

Drag Week 2011, 2012 & 2015. - BB N/A - 1977 Skylark w/Buick 455 EFI and TKO-600!
R100RT
Super MS/Extra'er
Posts: 1038
Joined: Thu Jun 30, 2011 12:45 pm
Location: British Columbia

Re: Baro fuel calculation

Post by R100RT »

I realize this post is somewhat stale and inactive for some months, however wanted to "wake up" a consideration of the going lean/ going rich discussion as elevations are changed. (my other recent post regarding "Baro Corrections" is clear).

"Suberimakuri" & "Nightstalker" both supported the "Going Lean as Elevation is encountered" through their experiences, while "TheSilverBuick" presents compelling evidence and experience to the contrary that richer fueling develops as elevation is encounterd.
What about both? As I recently operated up to around 4500 feet I was noting a richer development on restarts (guessing at 1 point lower via afr gauge, no lap top on trip). However as we continued towards 8000ft and higher, the opposite occured (2 points leaner) or more as EGO corrections were trying to help normalize. This is a turboed BMW boxer engine, no lap top on trip hence no logs.
As mentioned in my other post, I mitigated the wide swings by manually blowing ( :roll: ) into map hose while keying to force higher kPa snapshot.
The idea is that exhaust flows more easily at higher elevations, does the "double edge sword" behaviour of mine suggest something worthy of note from a mechanical plumbing standpoint?
Or perhaps just a byproduct of the thought to be "zero effect" baro correction settings I had choosen and not been able to test here @ sea level?
2015-08-09_14.56.59.msq Baro Correction.msq
I realize this is MS3 and my microsquirt is MS2, however still curious.
1983 BMW R100RT Motorbike
Turbocharged - Water/Meth
Sequential Ignition & Fuel
"Perky Sleeper" that excites bike enthusiasts once discovered (or being passed)
Newest project - 1995 BMW K75 is V3 Microsquirt, "Turbocharger - Of Course"
jsmcortina
Site Admin
Posts: 39585
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK
Contact:

Re: Baro fuel calculation

Post by jsmcortina »

R100RT wrote:I realize this is MS3 and my microsquirt is MS2, however still curious.
It's the exact same calculation (and change.)

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
R100RT
Super MS/Extra'er
Posts: 1038
Joined: Thu Jun 30, 2011 12:45 pm
Location: British Columbia

Re: Baro fuel calculation

Post by R100RT »

Guess I missed the bus on this discussion, will push onward and post anything I find.
1983 BMW R100RT Motorbike
Turbocharged - Water/Meth
Sequential Ignition & Fuel
"Perky Sleeper" that excites bike enthusiasts once discovered (or being passed)
Newest project - 1995 BMW K75 is V3 Microsquirt, "Turbocharger - Of Course"
AbeFM
Super MS/Extra'er
Posts: 875
Joined: Wed Dec 05, 2007 1:40 pm
Location: San Diego, CA
Contact:

Re: Baro fuel calculation

Post by AbeFM »

subwoofer wrote:I once made the mistake of having initial baro on while running VEAL, driving down a mountain. VEAL pulled a LOT of fuel all over the place, and everything was hunky dory until I had to stop at a service station. Restarted the engine and it was undrivably lean. It took some time to figure out what had happened, I actually thought the FPR or an injector had quit on me.
Years ago on MSIIx I couldn't get my car to start at 10,000 feet. Probably took me half an hour, finally I just bumped either VE or REqFuel by some 50%, and watching the AFR's kept adjusting as I went downhill to sea level. I *think* it was getting leaner as I went down (since I forgot to watch it for a while, it was VERY lean. Burnt pistons that showed up a week later may or may not have been related).

Now with MS3Pro I have no baro - but I can say that some days it runs just awesome, and some days I feel like the car will barely get there. The number of unsolved issues - like idle and flex fuel and other lingering doubts means I never even know what to checkm or why something is running poorly.

Certainly I will keep an eye on AFR's now that I know to look. What firmware has the best chance for working well here: The latest Beta or the release 1.4.0?

elaw wrote:Hey just a random thought... does the "initial MAP reading" code run when there's a sync loss?
Thankfully there's a "ignore out of this range" value - as often I'll just restart the motor while driving since sometimes this brings the performance back.
2000 VVT Miata turbo, MS3Pro

Contact me if interested in a MS-II 2nd gen NB Miata PnP board.
jsmcortina
Site Admin
Posts: 39585
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK
Contact:

Re: Baro fuel calculation

Post by jsmcortina »

If you want accurate baro then add a second sensor.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
AbeFM
Super MS/Extra'er
Posts: 875
Joined: Wed Dec 05, 2007 1:40 pm
Location: San Diego, CA
Contact:

Re: Baro fuel calculation

Post by AbeFM »

That was when I HAD a second sensor. I didn't miss it in this build because it seemed to cause more problems than it solved.


It sounds like 1.4.0 and up have this fixed? I could certainly add one, I just wanted to find out if things would be better or worse if I added one.

Is my fueling more likely to be accurate with the baro installed?
2000 VVT Miata turbo, MS3Pro

Contact me if interested in a MS-II 2nd gen NB Miata PnP board.
suberimakuri
Master MS/Extra'er
Posts: 632
Joined: Sun May 02, 2004 2:16 pm
Location: Auckland, NZ
Contact:

Re: Baro fuel calculation

Post by suberimakuri »

Definitely more accurate.
Measure the variable and build curve to suit your setup.
ol boy
Super MS/Extra'er
Posts: 1532
Joined: Mon Sep 10, 2007 3:06 am
Location: Tucson, Az

Re: Baro fuel calculation

Post by ol boy »

Does the latest MS2 and MS3 codes (3.4 and 1.4) have the extra division removed from their code? My baro correction looks like a right to left water fall. With the correct math applied should I expect a more linear baro correction?
306 SBFord, Torquer II EFI intake, 60 lbs injectors, 8 LS2 coils, VS Racing 7668 turbo, 4R70W, MS3x fw1.4 w/built in trans controller.
AbeFM
Super MS/Extra'er
Posts: 875
Joined: Wed Dec 05, 2007 1:40 pm
Location: San Diego, CA
Contact:

Re: Baro fuel calculation

Post by AbeFM »

Yeah - that's kinda my question - what's the "basic default assumption" that would let you get a "it's a lot better than nothing" correction put into place?

If there's a reasonable "best guess" then I'll hook up a BARO and put it on. If it's as likely to make things worse as it is to make them better then I'm happier without it. If the initial reading WORKS, I'm happy to use it, knowing that if I do a significant altitude change that I should power cycle the computer once in a while. Totally reasonable, but my concern is that doing so will make it worse than just shutting it off.

Can someone tell me if I'm better off using initial read versus doing leaving it off? If I add another sensor, how do I set it up so it doesn't lean when it should enrichen?
-Abe.
2000 VVT Miata turbo, MS3Pro

Contact me if interested in a MS-II 2nd gen NB Miata PnP board.
suberimakuri
Master MS/Extra'er
Posts: 632
Joined: Sun May 02, 2004 2:16 pm
Location: Auckland, NZ
Contact:

Re: Baro fuel calculation

Post by suberimakuri »

If you put a second sensor in you can adjust curve to make it do whatever you want with elevation changes.
Just like water temp correction.
ol boy
Super MS/Extra'er
Posts: 1532
Joined: Mon Sep 10, 2007 3:06 am
Location: Tucson, Az

Re: Baro fuel calculation

Post by ol boy »

I have a second sensor. I've always wondered why my curve was so crazy looking.
306 SBFord, Torquer II EFI intake, 60 lbs injectors, 8 LS2 coils, VS Racing 7668 turbo, 4R70W, MS3x fw1.4 w/built in trans controller.
Post Reply