math to calculate mpg from injector pulse width - Page 2 - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 05-15-2008, 10:56 AM   #11
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
Whoops, come to think of it, the vacuum bias on the FPR really only compensates for the manifold vacuum the injector is spraying into.
__________________

__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Old 05-15-2008, 01:34 PM   #12
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
correct. there's nothing electronic about it. it's just a spring loaded diaphram.

obviously the problem is that at high vacuum the fuel pressure is about 8psi lower than at ambient/low vacuum. that number even varies between honda engines with DOHC VTEC typically having fuel pressure at 50psi ambient versus ~42 for SOHC and non-VTEC engines
__________________

__________________
EH3 is offline   Reply With Quote
Old 05-15-2008, 01:47 PM   #13
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
Yeah there's 8psi less push, but 8psi more suck on the other side of the injector.
__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Old 05-15-2008, 01:50 PM   #14
Registered Member
 
Join Date: Jan 2008
Posts: 152
Country: United States
Quote:
Originally Posted by EH3 View Post
obviously the problem is that at high vacuum the fuel pressure is about 8psi lower than at ambient/low vacuum.
Correct. But, since the manifold is 8psi lower (due to the vacuum) the amount of fuel flowing per % of on time is the SAME as if you were at WOT and there was no vacuum (and higher fuel pressure to match!)

Should be able to calculate fuel consumption soley based on the injector's duty cycle and rated flow at your operating nominal fuel pressure. The catch is, some of the 'on' time is taken up by the amount of time it takes to open (and close) the injector, during which time it's not flowing at 100%. There should be some math to correct for that effect, which is primarily noticed at very low duty cycles...
Dalez0r is offline   Reply With Quote
Old 05-15-2008, 05:38 PM   #15
Registered Member
 
Join Date: Mar 2008
Posts: 408
Country: United States
dalezor: "Should be able to calculate fuel consumption soley based on the injector's duty cycle and rated flow at your operating nominal fuel pressure."

That idea makes sense to me, and it seems like a very good way to calculate fuel consumption.

There seem to be a bunch of products/systems that do it in a way that seems to be inferior: they calculate fuel use indirectly, based on airflow. I think they do it this way because they're relying on OBD2, and OBD2 delivers airflow data, but not injector data (I'm talking about generic OBD2; the statement I made doesn't apply to certain specific manufacturers). SG is an important example of a product that seems to have this problem (although it has many other strengths).

Anyway, does anyone know of any existing product/system that does it the 'right' way? I'm a little surprised that I'm having a hard time finding such a thing.

Of course one example of a project doing it the 'right' way (in this regard) is this one:

http://forum.ecomodder.com/forumdisp...mputer-26.html

Any other examples?
monroe74 is offline   Reply With Quote
Old 05-15-2008, 05:45 PM   #16
Registered Member
 
Join Date: Mar 2008
Posts: 408
Country: United States
The SuperMID, of course. I forgot to mention that one (as an example of a product that watches the injectors).

Any others?
__________________

monroe74 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuelly API, Remote Update hufman Fuelly Web Support and Community News 6 11-26-2017 11:28 AM
Not very precise mpg calculation larjerr Fuelly Web Support and Community News 4 08-20-2012 02:03 AM
Keeping my distance in traffic khurt General Fuel Topics 8 09-07-2008 04:23 AM
Electrical power and cars. DracoFelis Automotive News, Articles and Products 2 09-16-2006 02:31 PM
Honda TPS Sensors - $15/ea Matt Timion For Sale 7 06-27-2006 12:05 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 10:04 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.