I swapped out my 91's WC T-5 over the weekend for a freshly rebuilt one to use while mine is getting upgraded. The WC T-5 I got was out of an 89, which apparently used a mechanical speedo. I found out the original rear was a 3.08, I'm currently running my factory 3.42 gears (but may change to 3.73 soon).

So, here's my questions: Can't I just adjust the VSS setting in my prom to factor in the "higher" gears I actually have? Right now the speedo is ready higher than it should, meaning it's seeing a lot more pulses per mile than it should. I pulled the VSS off my T-5 and mounted it in the "new" T-5, so the only variable is the internal drive gear on the new tranny. Would I just change the original 4007 constant by the ratio of the 3.08 to 3.42 rear gears, or should some other ratio be used?

Is this a legitimate way to adjust/address this problem?

Hope somone can help out on this, doesn't sound like that hard a thing to me..... (which usually means I'm missing something!!!)

- Ye Old Phat Phart, Vern

 

if i understand what you want to do, then yes.

take a look at this thread,. https://www.thirdgen.org/techbb2/sho...hreadid=285897
the 8th post down which is by pwdbychevy has a pic of Tunerpro with the Super_8dm2.ecu file, it shows in the constants table "Vehicle Speed Sensor" which is right above the one he has highlighted, you should be able to change that to what i think should be a lower value than what it is set at now to get your speedo close, how close you can get i don't know, you will probably have to do it as trial & error & see what works best.

the 8d_v03.ECU file shows the "Vehicle Speed Sensor" constant as a number, 0 - 255, which for me is easier to set than Super_8dm2 which show it as pulses per mile.

 

Got a slight problem I thought would be easy to fix, but apparently not. Running a 91 'Bird with the VSS on a 730 ECM with SD.

I did a temporaty change of Trannies over the weekend so I could get my original T-5 "beefed up". Problem is the WC T-5 I out in had a mechanical speedo drive. So I just bolted up my VSS module from my original tranny. Went into TP-RT, played with the Vehicle Speed Sensor pulse constant, and discovered if I used the ratio of my rear gears divided by the gears in the car the rebuilt T-5 came from, that the computer is now seeing the correct (or very close to it) vehicle speed. Calculation, for other folks to use was:

(My rear gears ratio)
----------------------------- x 4000 = new constant VSS value
(donor car's gear ratio)

3.42
------ x 4000 = 5011 new VSS constant value
2.73

Now my only problem is the instrument panel (speedometer). It's still reading really high. I tried increasing the "VSS Instrument Panel Pulse Divisor" in TunerPro RT, but that doesn't seem to have worked. For one thing, the ECU info actually uses it as a multiplier. The default value appears to be zero. When I changed the value, the speedo quit working at all, the ECM no longer reports any vehicle speed in the ALDL output, and it even set an error code for "vehicle speed reading too low".

Has anyone ever got this to work?

 

Figured this may have gotten lost with the April Fool's board, so re-asking it.....

 

No one has managed to do this????

 

Sorry I can't be of any help but I'm curious about this as well, just for the pure fact I've got a t56 with a dakota box and I'd like to ditch(sell?) the box and use the ecm to "read" the right speed...

 

strange, your speedo should show close to the same speed as what the ECM shows in the data stream, changing the Vehicle Speed Sensor setting by itself should change both the speedometer & ECM readings the same amount & in the same direction.

i don't know just what the "VSS Instrument Panel Pulse Divisor" does, i had thought it would change the output to the cluster, to either increase or decreases the output to the speedometer & nothing else. seems you have show other wise.

maybe start over with the bin file from before any speed changes & just change the Vehicle Speed Sensor & see what happens.

 

Here's what happens when I did some tooling around with the vss panel divisor:

Bit 7 checked (128) = Speedo barely moves at 40mph
Bit 6 checked (64) = Speedo moved a little quicker at lower speeds but reading was still way off
Bit 5 checked (32) = same
Bit 5 and 6 checked = Speedo still way off

Didn't make any sense to check any other ones because Iknew the reading was still off by at least 20mph. Just for giggles I entered 16 in Bit 4 and checked it and the car stalled at idle. Time to get an SGI-5.

 

Yep, I'm trying to find one right now at a good price. Apparently they raised the $$ to around $90 on them...

 

I got mine for $89 incl shipping on their website.

 

I found that when I create a new ECU item and check the "flags box like the thread showed and then go to the vss panel pulse divisor and drag the bar all the way to 255, all of the boxes are automatically checked in the new ecu item I created.

 

I was under the impression that the setting changed the output that normally goes to the cruise control. (some use that output for speedo as I recall) The normal input to the ecm is 4000 pulses per mile and the output from the ecm to the cruise is 2000 pulses per mile.
I haven't messed with that (or need to) because my speedo is cable driven. I was just helping to get the item definition to work.
Maybe you still need to use one of those buffer dohickys?

ps, setting the "word" value to 255 would cause all the bits to be checked. The definition I was indicating should not be adjusted that way. Just individual bits to select the divisor/multiplier (or what ever it does)

 

is there a way that you can do without the vss. i swaped the gauges out and went with mechanical ones and the car was orginaly a carb. i went with a holley stealth ram and t56 trans and i dont have a vss. anyways around it. do i need it??

 

See chapter 11 in the Prom Tuning guide book and FAQ stickie up top.

 

Yes you need a VSS. I am running a 1967 327 in a 1977 Camaro, with a Stealth Ram. I assumed I didn't need a VSS when I first did the conversion, and I was never satisfied with the IAC throttle follower routine. I added a $70 Jaguarsthatrun.com conversion VSS, and bingo, now the IAC throttle follower varies correctly with vehicle speed. Also, you won't be able to use highway mode fueling or DFCO without a VSS.

 

And the Dakota Digital box is pretty easy to install (at least mine was).

 

Mine was also easy to install but every now and then I'm getting some kind of interference to where my speedo shows variable readings between 10-30mph while at a stand still. I have an inline noise filter installed but still have the problem. Anyone else having this problem? This is how I have it wired:

 

Yes. According to DD technical support, it is typically caused by interference from an ignition source on the VSS signal wires (in or out). They also said that the VSS wires coming from the transmission tailshaft need to be twisted around each other.

For me, it was ignition related since I have a 727 ECM under the hood on the passenger side. I mounted the wires running from the DD box (mounted under the steering column) to the ECM (mounted on pass side inner fender) on the firewall and it solved my problem. My application is probably different than most setups on this board, but I would look for something crossing or adjacent to the signal wires (in & out) that may be causing some interference. Ed

 

I have the wires twisted but still have the problem. I'm thinking that signal wire maybe routed too close to the tach or coil wire under the hood. I'll have to reroute it directly to the ecm under the dash instead and see what happens. The signal wire goes out to the engine harness under the hood and then back inside the car under the dash. I figured I'd try a "shortcut" to see if that helps.

 

I get an occasional 5 or so mph blip when sitting at a stop as well. I'll try twisting my wires to see if that helps. my wires are only 24 inches long - I spliced into the harness 3 inches from the ECM and have if along side my console temporarily....

 

in your diagram you show the box and how it is hooded up. question is where does the wire conector plug into (the purple and yellow wire) i have a custom harness made and has one wire in it that goes to vss. do i need to buy the dd and a vss also.

 

The connector plugs into the VSS on the rear of transmission. The purple wire is just a ground wire and is not needed since the ecm is already grounded elsewhere. That's probably why your harness only has one signal wire instead of 2. You will probably need to get a VSS.

 

one more question, what kind of vss do i use. i have the t56 aftermarket version and i am using the regular t5 nylon gear for my speedo. what do i need to buy and do you have anypart #'s.

 

I don't know any part #'s since i still have a T-5. The DD box hookup wiring maybe on a different output for your application. Do a search in this forum for the t56 vss. They're in here somewhere.

 

thanks for the help ill do a search and see what comes up