[Gmecm] ALDL MPG Information

Fri Dec 2 00:17:25 UTC 2005

Hi guys!

Great information here!   Those links that Greg Etchell sent are great too!

I actually, oddly enough, have a 1986 Jaguar XJS that has the in-dash 
computer.  I do want to rip out the V12 and put a small block in it 
someday and will need to modify it to work - or just go nuts and rebuild it.

Thanks for the formulas and great info!   I'm going to start drafting 
some circuits soon - I'll share with the group what I got when I get 
it (or when I get questions!!!!)

Thanks again!!
Kris

>You can calculate MPG quite accurately from the values available in
>the ALDL stream.
>
>Since you have a vacuum referenced fuel pressure on TPI cars, the
>injector flow rate is fairly constant, and the following calculation
>should be accurate enough for casual use. You're not going to create
>a lab instrument with this, but it will be the equal of typical
>factory fuel economy computers.
>
>You need three variables from ALDL:
>
>BPW
>RPM
>MPH
>
>and two constants
>
>Injector flow rate (volume per ms)
>Number of injectors on engine
>
>WIth this information, you can calculate as follows:
>
>BPW * injector flow rate * # of injectors = fuel per rev
>
>then:
>
>fuel per rev * RPM = fuel per minute
>
>finally:
>
>fuel per minute / MPH / 60 = fuel per mile.
>
>Cram it all together and flip it over to get miles/gal and you get:
>
>MPH / (BPW * injector flow rate * # of injectors * RPM * 60) = Miles
>Per Gallon
>
>You will need to make sure the units (ms/sec/min/hour, etc)  all line
>up when you do the calculation, but that is how it is done. You will
>probably also also need a fudge factor to dial in the calculation and
>account for variances in the fuel system components.
>
>In the 80's Jaguar used a purely analog version of this idea for the
>in-dash display. It didn't even receive data from the computer,
>rather it was wired directly to the injector harness. Aside from
>normal car-to-car variance in manufacturing tolerances, it was
>acceptably accurate. You could theoretically do the same thing with
>your micro-controller box by tapping the injector harness, VSS and
>TACH leads to accomplish the calculation thing without ever touching
>ALDL at all.
>
>-Gary
>
>
>
>On Dec 1, 2005, at 2:08 PM, Greg Etchell wrote:
>
>>You might be able to modify the ALDL stream to output the
>>calculated airflow
>>or injector pulse width or other internal variables.
>>
>>Injector pulse width and speed might give a Rough mileage value.
>>Probably
>>not to accurate but with some tuning it might be close....
>>
>>g
>>
>>-----Original Message-----
>>From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org]
>>On Behalf
>>Of lostrecep tion
>>Sent: Thursday, December 01, 2005 1:01 PM
>>To: gmecm at diy-efi.org
>>Subject: RE: [Gmecm] ALDL MPG Information
>>
>>those are very interesting articles is there anyway to derive mpg
>>with a TBI
>>computer 1227747  being as it does not have MAF ?
>>
>>
>>>From: "Greg Etchell" <Greg at WildoaksRanch.com>
>>>Reply-To: gmecm at diy-efi.org
>>>To: <gmecm at diy-efi.org>
>>>Subject: RE: [Gmecm] ALDL MPG Information
>>>Date: Thu, 1 Dec 2005 09:20:01 -0800
>>>
>>>Check out
>>>
>>>http://www.circuitcellar.com/avr2004/wabstracts/A3805abstract.pdf
>>>http://www.circuitcellar.com/avr2004/wentries/A3805.zip
>>>
>>>It is kind of what you are looking for and it might give you some
>>>ideas.
>>>Let us know what you figure out!!
>>>
>>>G
>>>
>>>-----Original Message-----
>>>From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
>>>Behalf
>>>Of Kristoffer M. Hain
>>>Sent: Wednesday, November 30, 2005 5:57 PM
>>>To: gmecm at diy-efi.org
>>>Subject: Re: [Gmecm] ALDL MPG Information
>>>
>>>I meant TPI not TBI.  It's a Tuned Port Engine
>>>
>>>
>>>Kris
>>>
>>>>Hi!
>>>>
>>>>I have a 350TBI with a 1227730 computer and would like to know if
>>>>anyone has any information about gathering information for MPG
>>>>from it.
>>>>I want to connect the stream to a microcontroller to build an
>>>>outboard
>>>>display.  Ideas?  Thoughts?
>>>>
>>>>Thanks in advance!!!
>>>>Kris Hain
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>>
>>
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