math to calculate mpg from injector pulse width - Fuelly Forums

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

Reply
 
Thread Tools Display Modes
 
Old 05-14-2008, 07:42 AM   #1
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
math to calculate mpg from injector pulse width

i'm making some assumptions with this math. can anyone here confirm if what i'm coming up with is accurate or if my assumptions are correct?

this is specific to honda/acura OBD1 ecus


for this example:
rpm=3250
mph=59
pulse width as taken from ECU map based on load=.127ms=.000127sec
injectors= 240cc
1cc=.000264gal


my major assumption is that injectors pulse once per revolution. is that correct?


so, here we go:

cc/pulse=.03048
gal/pulse=.00000805196
gal/min=.026168
gal/mile=.0257327
mile/gal=38.86


based on the reverse math from known mpg based on my weekly fill-ups, the gal/mile calc above is spot on.


i'd like to use the above logic to request a change to FreeLog (popular honda tuning datalogging software). if the math is right and accurate, a free OBD1 honda realtime MPG display could be developed within freelog.
__________________

__________________
EH3 is offline   Reply With Quote
Old 05-14-2008, 07:53 AM   #2
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
But do you have a vacuum biased FPR? in which case you'll have to read MAP data and adjust for actual injection pressure.
__________________

__________________
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 05-14-2008, 07:58 AM   #3
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
yeah, trudat. good point. hmm... let me see what data i have.

to be truly accurate i'd have to account for IAT compensation, too.
__________________
EH3 is offline   Reply With Quote
Old 05-14-2008, 09:48 PM   #4
Registered Member
 
Join Date: Mar 2008
Posts: 408
Country: United States
eh: "f the math is right and accurate, a free OBD1 honda realtime MPG display could be developed within freelog."

I thought freelog depended on a connection via something like a Hulog (http://www.moates.net/documentation....ntation_id=25). Or is there a simpler way to use freelog? I don't want to hack my ECU, I just want to monitor some data in a simple way.

"pulse width as taken from ECU map based on load=.127ms=.000127sec"

When you say you got that data from an ECU map, do you mean via something like a Hulog? Or is there another way to do it?

Sorry if that's a dumb question!
monroe74 is offline   Reply With Quote
Old 05-15-2008, 03:39 AM   #5
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
yes, freelog connects via the logging header on the ECU. a hulog or DKU-5 nokia cellphone cable is required to interface with the ECU. at a minimum a 4pin header will need to be soldered to the board to log.

no, i opened up an OEM .bin for my ECU in CROME (free honda ROM editor) which is used for tuning fuel/timing. similar honda editors are hondata, uberdata, neptune, ecTune
__________________
EH3 is offline   Reply With Quote
Old 05-15-2008, 04:40 AM   #6
Registered Member
 
Join Date: Mar 2008
Posts: 408
Country: United States
"i opened up an OEM .bin for my ECU in CROME"

OK, thanks for explaining.

I'm dimly familiar with that world, mostly because of hanging out at pgmfi.org a little bit. I just stumbled across a page (http://www.phearable.net/tech/efibeginnerguide.html) that does a good job of explaining this business of hacking a Honda ECU.

For various reasons you can probably guess, it would be nice if I could find a .bin for my car (VX). But such a thing probably does not exist (outside of a lab inside Honda), because my ECU is not chippable. Right?

This is something I've wondered about, and I have a feeling you know the answer.
monroe74 is offline   Reply With Quote
Old 05-15-2008, 04:58 AM   #7
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
actually, i'm not familiar with the VX ecu board.

if i could see a picture of the board, i could tell you if it was. you're assumption about the .bin for it not being available is probably true. 99.99% of the individuals socketing/tuning ECUs aren't going for FE and aren't tuning a d15z1
__________________
EH3 is offline   Reply With Quote
Old 05-15-2008, 06:48 AM   #8
Registered Member
 
Join Date: Mar 2008
Posts: 408
Country: United States
"if i could see a picture of the board"

I wish I had one, but I don't.

I've seen lists of Honda ECUs that are considered chippable, and the d15z1 ECU is definitely absent from that list. So I'm going to assume that means I'm not going to find a .bin floating around somewhere.

Anyway, the numbers you posted are interesting and helpful, so I'll be paying attention as you continue your efforts. I'm also very interested in the accuracy issues that were mentioned (e.g., IAT compensation).
monroe74 is offline   Reply With Quote
Old 05-15-2008, 09:05 AM   #9
Registered Member
 
suspendedhatch's Avatar
 
Join Date: Apr 2008
Posts: 445
Country: United States
Send a message via AIM to suspendedhatch
Quote:
Originally Posted by monroe74 View Post
For various reasons you can probably guess, it would be nice if I could find a .bin for my car (VX). But such a thing probably does not exist (outside of a lab inside Honda), because my ECU is not chippable. Right?
Actually no, you can find a P07 bin. I have one on my computer. PM me if you want me to email it to you.
__________________

Civic VX, D15Z7, 5 Speed LSD, AEM EMS, AEM UEGO, AEM Twin Fire, Distributor-less, Waste Spark
suspendedhatch is offline   Reply With Quote
Old 05-15-2008, 09:42 AM   #10
EH3
Registered Member
 
EH3's Avatar
 
Join Date: Sep 2006
Posts: 70
Country: United States
i'm simply trying to nail down all the formulas so that my findings could be presented to the freelog programmers. IAT compensation is super easy to handle. the main trouble now is coming up with the appropriate scalar for final fuel injector flow based on changes in fuel pressure. that actually has a major affect on the accuracy of the calcs.
__________________

__________________
EH3 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 08:47 PM.


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