GM speed sensors & ECM suggestions

[Curtis L. Martin]

>  The 1st things that scares me are the vehicle speed sensor and the
engine
> speed sensor & position sensor. I would appreciate any input/insight into
> these obstacles like whether they use a magnetic missing tooth or hall
effect
> set-up, etc.

Nothing so complicated.  The speed sensors are either in the transmission
tailshaft (late model) or in the speedometer (early models)

The speedometer mounted ones use an photo sensor to pick up light from an
led being bounced off the speedometer basket.  A "Buffer" module amplifies
that and I believe the output is a square wave with a frequency of one
pulse per every half turn of the speedometer drive cable.  Signal level is
TTL.

Different sets of plastic gears inside the transmission calibrate both the
speedometer and the VSS signal to the rear axle ratio and tire diameter of
the car.  There are also aftermarket "buffer" boxes that will allow
adjustment of the VSS signal to a certain extent without swapping speedo
drive gears (messy task on a 700R4/4L60 transmission :)

Late model versions have the VSS signal generated right at the same place
the cable drive would have been plugged into the tailshaft.

The speedo drive gears are a reduction gear..so the speedo signal is always
a small percentage of the driveshaft RPM.  You could also get away with
hall effect sensors on one of the axles to fake a VSS signal.. the axle rpm
is probably within the same range as the speedo cable rpm.

Give me a little time and I can do the math to say what the frequency of
the VSS should be based on actual vehicle speed. 


 
>  Does anyone have a suggestion for a particular GM ECM that would work in
this
> application? Or any references available that might help me choose the
right
> one? Below is a list of requirements for this injection system.
>  -8 injector drivers for sequential injection
>  -Speed-density system (saves me the hassle of fabricating a tight intake
&
> MAF upstream of the air door.
>  -Ability to interface with a GM transmission control module (I'll be
using a
> 4L60E behind the engine)
>  -Can't be an EEPROM type GM ECM since the CarPROM software can't handle
those
> boxes.
>  -Knock sensor inputs (I think GM calls it ESC) since this engine will be
10
> to 1 CR
>  - And all the other stuff that should be a gimme on a GM box like Idle
air
> control, EGR control, canister purge control & cruise control servo
control.
> 
>  -- Michael Baxter, 74172.1164 at Compuserve.com


Sorry, can't think of any GM computer that will meet all the requirements
you listed.  All of the ones I'm familiar with will do everything except
the sequential injection and connection to the 4L60E.  The ones that meet
those two requirements are EEPROM style calibration (except perhaps the
early LT1 Y-body & 4th gen F-body computers.. somewhere in the back of my
mind I recall that the first year of the 4th gen Camaro/Firebird having an
odd-ball computer that was still programmed via EPROM, not EEPROM...not
sure about that, you might want to get an informed opinion from a '93
owner)

You could make you life a little simpler by going with a standard
700R4/4L60 instead of trying to mate the 4L60"E".  That reduces the
transmission control from the ECM to just TCC activation.  You still have
all the benefits of an overdrive tranny with the only downside (if you want
to call it one) being the shiftpoints are adjusted via springs and
alterations to the valvebody, instead of electrically via the ECM.   I like
to think of the non-electrical 4L60 as being "better" than the "E"
model...but that's a personal point of view, since I learned how to adjust
the sucker the old fashion way (grr.."where did that damned 2-3 upshift
spring bounce too.." :)

You also missed one.. what are you planning on using for an ignition
system?  You are almost forced into using one of the computer advanced HEI
ignitions (either distributor based or Opti-spark) in order to make use of
the computer controlled timing (which has to be there in order for the
knock sensor to work)

Getting that Great GM Feeling yet? ;-)

Curt Martin (cmartin at america.com)
Ormond Beach, FL
http://www.america.com/~cmartin
'87 350 TPI Camaro, '94 3.4L SFI Camaro