[Gmecm] ALDL MPG Information

[Gary Evans]

If you are thinking of turning your XJS onto a "lump" ;-) here is the  
definitive resource on calibrating the trip computer for a V8:

http://www.jag-lovers.org/lumps/faqs/tripcomputer/index.html

-Gary


On Dec 1, 2005, at 4:17 PM, Kristoffer M. Hain wrote:

> 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
>>>>> _______________________________________________
>>>>> Gmecm mailing list
>>>>> Gmecm at diy-efi.org
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