Help needed reading Ford EEC-IV data stream

[Daniel R Burk]

>
>>
>>It could be that error codes are all that it stores -- kinda like
>>my 85 Grand Prix used to do (it used to not have a serial data pin on the
>>ALDL connector)  ...  I've priced the Diacom and think it is a little
>>high --- So I'm gonna try to build my own version (at least I'll learn
>>something in the process -- that should be worth something)... ...
>>It could be that Diacom just doesn't interface to the Ford EEC-IV and they
>>are just telling you that it only stores error codes. ...  Do you have a
>>shop manual for the car?  And, does it show a "serial data" pin --- if
>>so, it should be able to communicate some how to a pc...
>>
>
>I have a 1984 Riviera (probably similar to your Grand Prix) and also
>thought that it did not have a serial data pin and only stored error codes.
>However, I took the car to a mechanic friend of mine who hooked a scan
>tool (OTC I think) to the ALDL connector and was able to read the TPS
>voltage on the display!
>
>I would love to know how this is done and perhaps build a PC interface, I
>got a lead from auto.tech newsgroup about a device called device called
>AutoXray,  contacted one Bill Miller (wjm at goodnet.com) who apparerntly
>works there and asked him how you get data out of thesee cars, this was his
>reply:
>
>  Lloyd:
>
>  In order to monitor data from a General Motors Car,  It is necessary to
>  enter into an agreement with GM to get the data and protocol by which the
>  card communicates.  Once that is accomplished There is much product
>  development work.  The AutoXray XP240 should serve your purposes well
>  because of its ease of use and affordability.
>
>I phoned them for an information package on there product but so far no
>reply (almost a month).
>
>If anybody knows how this data is extracted please let me know, just for my
>peace of mind.
>
>Lloyd Ferguson
>CBC Engineering
>7925 Cote St. Luc Road
>Montreal, Quebec
>H4W-1R5
>Tel:    (514)485-5340
>Fax:    (514)485-5364
>E-mail: ferguson at srcing.login.qc.ca
>
>
>
>

Lloyd: What he has not told you is that the '84 Riv uses an ALDL interface,
which is termed "Assembly Line Diagnostics Link".  It is in essence, a
one-line serial data link that spits out information at something like 46.7
Kbaud. (from memory. be warned.)

The data is tagged with a two-byte address code, followed by a one byte data
code that represents the current data value. (Again, from memory, NOT from
experience!!)  

The two-byte address code is just that, an address.  Each ECM function has
an assigned address.  So, if you knew the address of, say, throttle
position, you could scan the ALDL line for the moment when that address came
up, and grab the current status of throttle position. My guess would be that
it would be a value between 00 and FF, corresponding to 0% and 100% throttle
opening.

--- Dan.