PUL/MILE and speed DIVISOR understanding

[Bruce Plecan]

----- Original Message -----
From: Mike Rolica <mrolica at meridian-mag.com>
To: <gmecm at efi332.eng.ohio-state.edu>
Sent: Monday, November 29, 1999 2:01 PM
Subject: RE: PUL/MILE and speed DIVISOR understanding

1227730 (AUJP)  to use optical speedo sensor (2,000 ppm), 0018 from D8 to
98, and speedo input to C-6
Grumpy

| Yes you are correct.  Changed  the valve at 0015 to basically 2000, to
make
| up for optical sensor  (2000ppm )and also changed another bit  .. forget
| where it is.... Bruce will know as it is an option flag for either optical
| or mag speed sensor  Seems to work as I have tried a few chips with
various
| values. Tcc locks up sooner and sooner with lower value and higher with
| higher value, telling me this is what it does :-) Also have to change
input
| on ecm for differnet sensor type... bruce knows this as well.
|
| As for 0014 this is for the digital dash option used to calb signal to
| speedo  I think.
| Mike Rolica
| Meridian Magnesium Products
| Strathroy, Ont
| Ext. 260
|
|
| -----Original Message-----
| From: Marc Randolph [SMTP:mrand at pobox.com]
| Sent: Monday, November 29, 1999 12:24 PM
| To: gmecm at efi332.eng.ohio-state.edu
| Subject: PUL/MILE and speed DIVISOR understanding
|
| Here is something for both the beginners that want to learn
| about code and tables, and a question for those that already
| understand most of it:
|
| In the ANHT 90 L98 ECMGUY .pdf listing, there are two entries that
| I'm very interested in and was wondering if anyone could help me
| understand them better before I go blindly changing my PROM and
| getting myself really confused (or worse).  Here's the details of
| what I know:
|
| Two table entries of interest:
|
| 8014:   FCB $00    ; INSTRUMENT PANEL DIVIDER ARG
| 8015:   FCB 230    ; PULSE/MILE ROAD SPEED CONSTANT
|
| Code of interest:
|
| At code offset BEF7, the 8014 value is OR'ed with whatever is in
|
| memory location 0x32 (after 0x32 is masked with 0x0F right below
| BEE9).  0x32 appears to be a word that gets clocked out of
| the ECM serially (on YZ body, 0x32 contains, among other things
|
| I'm unsure of, a bit to enable the secondary fuel pump, and a
| bit to control the shift light), I assume to the CCM for display
| on the instrument panel.
|
| At code offset BF9A, the 8015 value is read into accumulator A and
| then multiplied by accumulator B (which contains a count of some
| kind from the vehicle speed sensor, read from memory location 0x8D).
| This is then divided by whatever is at memory location (0x8B).
|
|
| Concepts of interest:
|
| The ECM converts the vehicle speed sensor signal to 4007 pulses
| per second and feeds that to devices like the CCM, ABS, and ASR.
| The value at 8015, 230dec, is the internal representation of
| the 4007.
|
| My main question:
|
| When I go to install taller gears in my car, I'd like to modify
| the ECM to make up for the installation so that my speedometer
| reads the correct speed.  My initial guess is that I should change
| the value at 8015 so that the ECM puts out fewer than 4007 pulses
| per mile.  Since everything else is expecting 4007 pulses per mile,
| if I feed it a few less pulses, they will think the car is traveling
| slightly slower (which is true because of the taller rear end).
| Can anyone think of a reason this wouldn't work (or would do any
| harm)?
|
| Second question:
|
| Would the correct pulse / mile value be based upon a percentage
| of the original?  3.45 gears stock, 4.10 gears new, would result
| in an 18.8% difference - is that the right amount to adjust the
| pulses / mile?
|
| Third question:
|
| What in the world is the value at 8014 for?  Any ideas how much
| it would divide/multiply the speed by?
|
|
| Thank you, and have fun,
|
|    Marc
|
| --
|   Marc Randolph     -    mrand at pobox.com    -     PGP keyID:
| 0x4C95994D
|      If you have any info on the mid-60's car called the Bill Thomas
|        Cheetah, or know anyone that might, please contact me.
|