I am putting an Auto Meter electric programable speedo in my 91z28 and have the t56 tranny but I have no clue on how this needs to get hooked up the right way. There is an OUT and SIGnal on the back of the gauge. I need my ECM to read the correct pulses from the tranny. Does this auto meter speedo have the ability to correct itself for the different pulse rate of the t56? If so then can someone shed some light on hooking this up. the wire that use to go to the back of the OEM cluster should go to the ECM box correct? which direction does the VSS signal take after it leaves the tranny? Does it go to the ECM then gauge or what? where do the 2 VSS wires go to under the car?

 

The Autometer speedo can be calibrated to run off the T56 VSS (I know this because mine works great, and is accurate according to police radar) but to my knowledge, it can't convert the signal to the proper pulse rate for the ECM. This is what most T56 swappers buy the Dakota SGI-5 for.

To set up the Autometer speedo for the T56, here's what you need to do. Run one wire from the VSS to ground and the other to the "SIG" terminal on the speedo. Also run ignition power and ground to the speedo. Take the car to the beginning of a measured 2-mile stretch of road and shut the car off. Hold down the trip reset button while you crank the car. The needle should go to the middle and then peg out (I can't remember if it's high or low but it goes somewhere.) Press the trip reset again and the needle should move back to the middle. Drive 2 miles exactly. The closer you are to exactly 2 miles, the more accurate the speedo will be. When you get to the end of the 2 miles, press the trip reset button again. That's it, it's calibrated.

The original VSS ran through a buffer box to the ECM and from there to the gauge cluster. You DO NOT want to run the T56 VSS through this buffer, so you'll need to run new wires for the VSS.

 

i'm using an autometer elec. speedo with my t56 and don't have a sgi-5 box... car runs fine, ses light is on all the time, but if not running one effects how the car runs... it's very minimal and not noticable.

 

It'll effect gas mileage and idle quality mostly. When there's no VSS input the ECM will disable the highway mode fuel and spark tables which means you lose a bit of highway mileage. It also uses the speed input to help control the IAC when decelerating and a few other varied functions.

 

thanks for the tip greatJ. I just sold my SGI 5 box thinking I didnt need it anymore. How would I go about telling the ECM the PPM? what do I do with the orignal VSS wires that went into the old tranny? Is there anything that plugs into the OUT on the back of the speedo.
i do not believe my car has a buffer box. it is a 91.

 

I believe in '91 the buffer was built into the cluster, but don't quote me on that.

The OUT terminal on the Autometer speedo is for sending a filtered (smoothed out) VSS signal to any other device that needs it (i.e. aftermarket cruise control, or the ECM) but there's a big issue with the pulse rate....the T56 VSS pulses MUCH faster than the 3rd gen VSS, and the Autometer doesn't change the pulse rate...it just calibrates itself to work with whatever pulse rate it sees.

The stock VSS wires you can just leave hanging, or you can put the T56 connector on and cut them at the ECM end and use them to drive the Autometer gauge. Just don't hook the T56 VSS to the ECM. It'll have a duck.

If you're an electronics technician you can build a counter circuit to reduce the VSS pulse rate to something close to stock (roughly a 10:1 reduction IIRC,) but if you're not, that's what the SGI-5 is for.

 

Ok sounds good, Nowi have to buy a 2nd SGI 5 box. Now for a twist, Do I still hook up the SGI 5 box the way the directions say? There is a SIG and OUT on that box as well.

 

Hook it up like the directions, but to simplify the wiring you should be able to run the OUT terminal on the speedo to the SIG terminal on the SGI-5 instead of running it straight off the VSS.

 

ok so how does this sound:
ground 1 wire from the VSS on T56(shouldnt matter which one)
ground 1 wire from ECM VSS wires(shouldnt matter which one)
take 2nd wire from t56 VSS and connect it to SIG on speedo
connect the OUT on speedo to SIG on SGI-5
ground the SGI 5 box
power the box


where does the other wire from the OEM VSS wires go to?
what goes into the OUT on the SGI 5 box. should these 2 wires be connected together?

 

Yes they should. But it does matter which of the 2 stock VSS wires is grounded. One of them is a signal wire and the other is a reference...the ref wire should be grounded. According to my 7727 ('Vette) ECM wiring diagram, the ref wire is purple and the signal wire is yellow. I'm not sure if the 7730 (F-body) ECM is the same.

 

I though one wire was HIGH and the other was LOW. everyone on here running the SGI box ays it dont matter whick is grounded. How can I tell which one if the reference onmine? My colors are PPL and YLW as well.

does it matter which wire is what on the t56 connector?

 

On the T56 connector it doesn't matter, it's just looking for continuity. And the ECM may be fine with either wire grounded, I just know that my wiring diagrams show a distinct positive and negative, so I figure the negative should be the one that's grounded. It may just be a terminology thing and not really make a difference at all.

Since the wire colors are the same, I'm sure the functions are the same. I'd ground the purple wire.

 

ok I will take a look at this thiswekend. Thank you very much for the info onthis. I have been loosing sleep over this issue. You see, last summer I was driving the car with the t56 and no SGI 5 box and the SES light would come on all the time and when it did I could never get the car to idle when I stopped the car. well, one day the I guess the light came on and I didnt know and pushed the clutch in to coast into work and I had the radio one and dit feel the car stall. well, I had no brakes and no steering and ended up hitting an excavator at about 30mph. so,,,, I DONT want that happening again becuz of this speedo issue. but again, thanks I will sure to let you know how I make out in a few weeks with it. Now I just have to figure out with OUT to connect to on the SGI 5 box. trail and error I guess

 

I just took a look at the dakota digital website and it seems they have a newer version of the SGI5 box. it does more things but I read the directions and I dont think its gonna work right. I am gonna try calling them tomororw. What is the PPM of the t56 and the PPM I need to tell the computer?

 

I want to say the T56 is in the 20k ppm range, and the stock is like 2k. But I'm really not too sure on that. I know that the T56 VSS puts out 17 pulses per driveshaft revolution (counted the reluctor teeth when I had mine apart) so you could run the numbers and figure it out from there.

Can you shoot me the link for the new versino of the SGI-5? I'd like to take a look at it (may need something similar for my TPI 350 Jeep project.)

edit: I just ran the numbers and it adds up to more like 45k ppm for the stock T56, using 3.42 gears and a 26" tire.

 

http://www.dakotadigital.com/manuals/SGI-5B.pdf

 

Thanks for the link.

I'm pretty sure that would work...you'd have to hook up to output 3 and set the DIP switches to off/off/on/off and then use the calibration buttons to get it dead on. The only issue is that you need a scantool or something to see what speed the ECM is reading. You don't happen to burn your own chips, or know someone who does, do you? You should be able to use a datalogger to watch what speed the ECM sees.

 

I was just playing around in TunerPro and I noticed something. There is a constant in the ECM programming that tells the ECM how many ppm the VSS puts out. If you know somebody that can burn chips, it may be as simple as setting the ECM's VSS constant to match the T56 VSS. Then you wouldn't even need the SGI-5.

The stock setting on the constant is 4006.....and 4000ppm sounds like a real familiar number to me. It's adjustable from 3614ppm all the way to 460kppm.

 

I dont know anyone personal that burns chips. Is it as easy as changing the constants in the chip? I just got off the phone with Fastchip, they are custom programing a chip for my setup. This is the best i can do without driving the car somewhere to be perfect. Now I asked about this issue with the VSS and they told me it cant be done. Somehow I think there just rushing the phone call. They told me they programmed my new chip based off the 4 letter code I gave them of my OEM chip. Is it stil possible to have my OEM chip modified to fix the VSS even though I have thie new piggyback chip?

 

I think it all depends on which ECM and which stock program you're starting with. I'm putting a speed-density computer in my truck, and running a program that's based on the '92 AUJP code (although somewhat modified.) I know that I have a VSS constant that I can adjust, but since the motor's not in the truck yet I can't tell you for sure that it will do what you need. I'm fairly new to the whole chip tuning thing.

What was the 4-letter code you gave them to base the tune on?

 

my 91 HAD a 305TPI w/ a T-5 in it and I change it to a 350HSR and t56. I bought a prom for a 350tpi from the same year car. The 4 letters on the chip I have are AXYC. does that sound correct

 

Although there is a VSS constant in the calibration, you don't have much flexibility in how it's set. The constant is used to tell the ECM hardware what to do with the signal. I understand this hardware is set up such that there are only a few "valid" choices such as 4k or 2k PPM.

Maybe a fitting comparison would be the cylinder select calibration. While it would appear you have 255 possible selections to choose from, that's not *really* the case. The software is written so only a few are valid. Although, it might be interesting to see what it would do if you told it you have 8.12345564 cylinders...... Or, 255 cylinders......