[Gmecm] What does VSS do exactly?

Tue Jun 28 23:38:54 UTC 2005

Hi there!

That's what is on the trucks, too.  Perhaps my description wasn't clear...

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for now)

Rick McLeod wrote:
> Correct me if I'm wrong:
> 
> It may be different on trucks, but on the mid-late
> 80's Camaros there is a opto-buffer mounted to the
> back of the instrument cluster, a yellow box, wires to
> the opto sensor on the speedo, and an edge connector
> that the power/output lines connect to. It creates a
> ecm compatible 2K signal of square wave type.
> 
> --- Jay Vessels <jay at vessels-clan.com> wrote:
> 
> 
>>Hi there!
>>
>>The vacuum/electronic cruise system on the mid-80s
>>trucks was the servo 
>>underhood, the VSS+buffer, the turn signal stalk,
>>and a small black box 
>>which was the standalone controller.
>>
>>The underhood wiring did not have the VSS signal to
>>it; rather, it was 
>>just wiring for two vacuum solenoids, and for some
>>systems, a feedback 
>>signal (moving magnet/wire coil).
>>
>>I've never seen the VSS buffer mounted to anything
>>(seems like it just 
>>hangs in space) so I'd do just what you mentioned --
>>I'd remove the 
>>speedometer from the cluster, and follow the ribbon
>>cable.  Chances are 
>>you didn't remove the controller, so if you find
>>that (usually around 
>>the steering column) you'll find where the post-VSS
>>buffer wiring goes. 
>>  That harness already has power and ground, so it's
>>a simple matter of 
>>running a wire from your ECM to the VSS output wire
>>that's already there.
>>
>>You may be closer to having a VSS than you thought!
>>
>>Jay Vessels
>>1982 Chevrolet S-10 Sport, 2.8V6 TBI
>>1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for
>>now)
>>
>>
>>Charles McDowell wrote:
>>
>>>Well, I removed the cruise, but yes, I think I had
>>
>>the first kind you
>>
>>>described (no CCC though).  The speedo cable goes
>>
>>into the gauge in the
>>
>>>dash.  The cruise looked like a vaccum thingy
>>
>>controlled by wires.  So, you
>>
>>>are saying that my speedo is already doing the job
>>
>>for me probably?  In
>>
>>>principle, I could trace the wires from the speedo
>>
>>to the buffer and get VSS
>>
>>>from there.  Is that right?  Any guess where they
>>
>>typically mount these
>>
>>>things?
>>>
>>>Would the VSS signal go all the way out to the
>>
>>cruise stuff under the hood?
>>
>>>If so, since I removed the cruise, it would just
>>
>>be hanging open at a
>>
>>>connector and life would be incredibly easy...
>>
>>except for finding the
>>
>>>connection in the EFI harness.
>>>
>>>Thanks for the help.
>>>
>>>-----Original Message-----
>>>From: gmecm-bounces at diy-efi.org
>>
>>[mailto:gmecm-bounces at diy-efi.org] On Behalf
>>
>>>Of Jay Vessels
>>>Sent: Sunday, June 26, 2005 10:05 PM
>>>To: gmecm at diy-efi.org
>>>Subject: Re: [Gmecm] What does VSS do exactly?
>>>
>>>Hi there!
>>>
>>>A few questions:
>>>
>>>1)  Do you have factory cruise control?  If it's
>>
>>the vacuum/electronic
>>
>>>system (i.e. there is a vacuum servo cabled to the
>>
>>throttle that has about 4
>>
>>>or 5 wires to it, as opposed to the
>>
>>vacuum/mechanical system that had the
>>
>>>speedo cable routed to a module under the hood)
>>
>>then you already have a VSS.
>>
>>>1983 was a weird year for that, since at least
>>
>>some vehicles got the
>>
>>>electronic version.
>>>
>>>2)  Did it have the computer-controlled carburetor
>>
>>on it?  Some of the
>>
>>>California trucks did, and they would also have a
>>
>>VSS already.
>>
>>>If 1 or 2 is true, then the VSS is already there. 
>>
>>Find the VSS buffer
>>
>>>(small box, ribbon cable to the sensor, card-edge
>>
>>connector to the truck),
>>
>>>and the pin that's not 12V or ground is the VSS
>>
>>signal.  Hook it to the
>>
>>>ECM's VSS input pin and you're done.
>>>
>>>Barring that, 3)  Do you have the stock
>>
>>speedometer?  If so, VSS is simple.
>>
>>>The factory speedometer has a rectangular hole in
>>
>>the back of it with a
>>
>>>small hole to one side.  The VSS
>>
>>phototransistor/LED pair fit that hole and
>>
>>>is attached with a single screw.  Any 1981-1989
>>>(approximately) GM car with EFI or CCC will have a
>>
>>VSS in the back of the
>>
>>>speedometer (some FWD and later-80s cars exempted,
>>
>>just look for a
>>
>>>speedometer cable).  Grab it.  It will be a small
>>
>>black module attached to
>>
>>>the speedometer with a ribbon cable to a small
>>
>>box.  That box has a
>>
>>>card-edge connector with three pins.  Get the
>>
>>connector, too.  The connector
>>
>>>is ground, +12V, and the VSS output.  Connect the
>>
>>power supply to whatever's
>>
>>>handy, and run the VSS output to the ECM's VSS
>>
>>input pin.
>>
>>>Jay Vessels
>>>1982 Chevrolet S-10 Sport, 2.8V6 TBI
>>>1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for
>>
>>now)
>>
>>>Charles McDowell wrote:
>>>
>>>
>>>>You're probably right.  Can you (or anyone else)
>>
>>point me in the right 
>>
>>>>direction for VSS stuff for an 83 K-5 Blazer with
>>
>>a 350?
>>
>>>>I think the most pain will be that I bought a
>>
>>pre-made harness with no 
>>
>>>>VSS, so I'll have to dig into that to make the
>>
>>connections.
>>
>>>>Thanks. 
>>>>
>>>>-----Original Message-----
>>>>From: gmecm-bounces at diy-efi.org
>>
>>[mailto:gmecm-bounces at diy-efi.org] On 
>>
>>>>Behalf Of Jay Vessels
>>>>Sent: Sunday, June 26, 2005 3:34 PM
>>>>To: gmecm at diy-efi.org
>>>>Subject: Re: [Gmecm] What does VSS do exactly?
>>>>
>>>>Hi there!
>>>>
>>>>VSS does several things, and the newer the ECM the
>>
>>more things it's tied
>>
>>>to.
>>>
>>>
>>>>The older 1227747 vintage ECMs do several things
>>
>>with VSS, most 
>>
>>>>notably parking the IAC at speed, and I believe
>>
>>stall saver (i.e. 
>>
>>>>sudden throttle close, such as letting off the
>>
>>throttle and pushing in 
>>
>>>>the clutch at speed when coming to a stop).
>>>>
>>>>Newer ones such as the $A1 code in the '730
>>
>>(1991-1994 3.1V6 MPI) use 
>>
>>>>VSS to determine much more, such as throttle
>>
>>follower (manual shift 
>>
>>>>assist), stall saver, idle speed adjustment, spark
>>
>>advance, etc. since 
>>
>>>>that code changes fuel and spark strategy based on
>>
>>whether the vehicle is
>>
>>>moving.
>>>
>>>
>>>>Considering how simple it is to hook up (stock
>>
>>parts abound as do 
>>
>>>>aftermarket ones) and the benefits in drivability
>>
>>(which is a big reason
>>
>>>> to go EFI in the first place), why not connect
>>
>>it?
>>
>>>>Jay Vessels
>>>>1982 Chevrolet S-10 Sport, 2.8V6 TBI
>>>>1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for
>>
>>now)
>>
>>>>Charles McDowell wrote:
>>>>
>>>>
>>>>
>>>>>Thanks for the reply.  I always thought the IAC
>>
>>"parked" itself when 
>>
>>>>>the car was shut off.  Do I understand correctly
>>
>>that I will probably 
>>
>>>>>not have a problem if my computer is the type
>>
>>that operates that way 
>>
>>>>>instead of recalibrating above a certain speed?
>>
>>Is there any good way 
>>
>>>>>to tell which I have?
>>>>>
>>>>>-----Original Message-----
>>>>>From: gmecm-bounces at diy-efi.org
>>
>>[mailto:gmecm-bounces at diy-efi.org] 
> 
> === message truncated ===
> 
> _______________________________________________
> Gmecm mailing list
> Gmecm at diy-efi.org
> http://lists.diy-efi.org/mailman/listinfo/gmecm
> 