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| Was there a MPG display for Fiero Era GM vehicles? (Page 1/2) |
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Romsk
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JUL 10, 04:10 PM
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My Fiero ECM constantly spits out 5 data words when in Normal Mode.
In DMDIAG Mode, I get the 25 words and I know what they mean. I am referring to NORM Mode where 5 words come out of the ECM 160 baud pin when the ALDL Diag Select pin is left open (not grounded) like when just driving normally.
Recently I read that these 5 words may be for a MPG display that was not offered on Fieros, but maybe it was on other GM makes and models.
Is that true? Does anyone know what these 5 words mean?
The first word seems to be Mode Word 2 (just like in DMDIAG Mode).
So it down to just the 4 words after that.
Thanks
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Paul Romsky
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fieroguru
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JUL 10, 09:24 PM
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Several mid to late 80s cars has driver information screens. They were even working on a rally computer for the Fiero.
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buddycraigg
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JUL 10, 09:35 PM
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I don't know what you are trying to accomplish.
There were some cars with a needle, or a green/yellow/red light that responded to a vacuum sensor.
The less vacuum, the less fuel efficient you were.
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Romsk
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JUL 10, 09:41 PM
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Fieroguru,
Thanks. This is a piece of the puzzle. So there was such a device, at least on paper, so those Normal Mode words must somehow control it.
Cadillacs at the time had a unit that displayed Range, MPG Instant, MPG Average, and Fuel Used. That is 4 parameters, and there are 4 Normal Mode words after the MW2 word, so this is starting to coalesce.
This is a comment from my code as I investigate this and watch what it is doing from the ALDL data:
0 is WM2, 1 to 4 may be: Range, MPG Instant, MPG Average, and Fuel Used
as these were available in some GM cars like a Cadillac. Needs more research.
Words are indexed logically (from 0):
Engine Off:
0 MW2 0 Steady
1 192 Steady
2 0 Steady
3 X Alternates between 128 and 0 every couple of frames
4 80 Steady
Engine On:
0 MW2 X Varies 132:OLDCELL and REF625, 128:OLDCELL
1 X Varies Mostly:192, Sometimes:196, Rarley:128
2 X Counting 000 to 255 various steps, rolls around
3 X Alternates between 128 and 000 every couple of frames, sometimes 001 and then 129
4 80 Steady
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fierofool
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JUL 11, 08:25 AM
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An ECM from a Beretta might have that function. I believe it used the 7730 ECM. My wife's 88 Beretta GT had a digital instrument panel and a convenience center that told temperature, current mpg, average mpg, miles to empty, and other info.
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Romsk
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JUL 11, 01:28 PM
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buddycraigg,
I developed an ALDL Diagnotic Tool for Fieros. One of my users is asking me how to interpret the 5 bytes (9-bit words) the ECM spits out when in Normal Mode (NORM) .
There is no official GM documentation on the ALDL. So, for DMDIAG, DMFACT, and DMALDL Modes, I have done tons of research on what those modes spit out and I know what they mean. It is only NORM Mode that I have not yet figured out. All I know is (and it is just a clue at this point) that the NORM data "may" have been for a MPG or Rallay display or something like that, but GM never brought it to fruition for Fieros. Some Cadillacs at the time had a simple 4 parameter MPG display. Since I am seeing 5 bytes, I figure that the Fiero data may be close to that (as GM probably shared ECM software among models). Another poster showed me a drawing of a Rallay Display for Fieros (which I don't think we're ever made). But any clues can help at this point.
In my other posts, you can see what I am getting from the ALDL in Normal Mode.
So my question is what do those 5 bytes of data mean that come from the ECM when in NORM Mode.
If you are not familiar with the details on how the Fiero ALDL works, then you may not be able to answer, but I appreciate the effort.
Thanks,
Paul
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Romsk
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JUL 11, 01:45 PM
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fierofool,
Thanks, that may be another clue. I am guessing the Normal Mode byte stream from the Fiero somehow refers to the most rudimentary of MPG displays - like what Cadillacs used at the time.
The data might have been for the Rallay Display they were working on for Fieros, but from what little we know about it, it was a comprehensive display and never offered, I am only seeing 5 bytes across the ALDL in Normal Mode, MW2 is clearly the first word, so the other 4 that follow are the "nuts I am trying to crack".
It may require finding an Fiero era GM car with a simple 4 parameter MPG display, putting an o-scope on it and capture the data stream from the ECM as another clue as to what Fieros are spitting out.
There are a few forum members that know the Fiero ECM code inside and out, if I can reach one of them I am sure they can look in the code and see what the ECMs are spitting out in Normal Mode.
Do you know of any such members?
Thanks,
Paul
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theogre
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JUL 11, 04:00 PM
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Rare to find "info data" display because mostly only installed on some High $ models.
Go dig thru Cadillac, Vet, and some other models in the 80's.
If tied to ECM, then should show in FSM and Maybe AllData because most data there is copy/past from FSM and have TSB too.
| quote | Originally posted by buddycraigg:
There were some cars with a needle, or a green/yellow/red light that responded to a vacuum sensor.
The less vacuum, the less fuel efficient you were. |
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Doesn't need a sensor/sender. JC Witless and others sold a simple Vac Gauge relabeled like this w/ long tube kit so can watch it anytime. Some cars had them built into the dash pack w/ rest of gauges.
Some Vac Gauge for shop use have marks when have a "problem" at idle w/ different low vac for stuck valve(s) etc and even for "MPG."------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
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Romsk
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JUL 11, 04:28 PM
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theogre,
Thanks, I will do some more digging.
It could be 1 of these 4 bytes are for some kind of vacuum indication. The ECM does report MAP in ALDL Mode, and I do display that in both Absoulte inHg, and relative from standard 1 atmosphere inHg (so called vacuum), so the ECM could be spitting that out (or related value) in Normal Mode.
I will keep looking to see if the stream ever correlates to vacuum.
Do you know of anyone that has dug into the ECM code, maybe one of those that have made performance PROMS? I am sure someone could take a look at the code and see what these Normal Mode bytes are for.
It would take me months for find the ECM schematics, source code, and reverse engineer it (and weed through conflicting/incorrect info buikt up over the years). Someone must have done this already.
Thanks,
Paul
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Fie Ro
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JUL 11, 05:50 PM
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