OK T56 swap guys...really need some help here. I am attempting to avoid purchasing the Dakota Digital converter box after my T56 swap by adjusting the bit settings for the VSS in my 1992 RS with a 1228746 ECM. Take a look at the following web page that I believe was written by Dave Zug (thanks for the T56 shift pattern indicator plate, by the way):

http://www.eecis.udel.edu/~dzug/92z2...0-vss4T56.html

Dave was working on a 1227730 ECM, but I was guessing that the same logic applies to the 1228746 ECM. His VSS bits were numbered b7, b6, and b5 while my bits are number b6, b5, and b4 (see attached image). He was able to get his speed pretty closely corrected by setting bits b7 and b5, so I used the logic that I could get my speed close by setting bits b6 and b4...WRONG! I'm still pegging 110 mph (max speed on my speedo) when I'm going about 5 mph down the road. Of course, this is tripping my speed limiter and killing fuel to the motor, thus rendering the car useless.

Does anyone know which bits to turn on/off to get the speed pretty close? I'm running a 3.08 gear with 275/40R17 tires, by the way.

One other thing...my SES light is constantly flashing while the car is running. I have checked the trouble codes and it gives me the "12" code first (which indicates the ECM is working properly) followed by the "51" code which means there is either a PROM or ECM problem. This may be from when the legs on the EPROM chip were not properly lined up the first time I popped it in, though.

 

You can't do what you are attempting. The '8746 doesn't have the same hardware as the '730.

First thing is to go to the 'patch method demo' sticky up top and apply the rev-limiter patch. That will protect your engine while allowing you to drive the car (also apply the code43 patch from same thread).

As for the speedo, a DRAC may work to correct the problem. Used ones can be found in "automotive recycle yards" (that was supposed to be a funny). If diy-efi ever wakes up there is a pdf file on incoming that details the calibration jumpers on the DRAC.

(Anyone here ever use a DRAC for the T56? Does it work?)

Else it will be the Dakota Digital . . .

RBob.

 

As for the flashing SES, if a rapid flash, then you didn't checksum the bin after you modified it, or the chip isn't seated properly.

RBob.

 

Thanks a ton, RBob...glad to know that it wasn't some crazy electrical problem causing the bit change to not work. Oh well...it was a good learning experience .

As for the DRAC (took me forever to figure out that meant Digital Ratio Adapter Controller), I did tons of searches on thirdgen and all over the internet but found very little. The only site of interest I found was http://www.birfield.com/archives/htm...msg02087.html, but I'm not sure if it is relevant. On first read of the thread, I thought it was indicating that the DRAC from a 93-95 TBI truck would work...but I think I'm wrong. Most of what appeared to be "good" information on my search engine was located on the diy-efi site, which is STILL down.

While we're on the subject of VSS, there seems to be some confusion about the VSS output on a T56 and the expected VSS input for the ECM and speedometer. There are two ways of expressing thing signal: pulses per mile and pulses per driveshaft revolution. From what I've read, the T56 outputs 40,000 pulses per mile, the speedo needs an input of 4,000 pulses per mile, and the ECM needs and input of 2,000 pulses per mile. However, I have also read that the T56 outputs 40 pulses per driveshaft revolution, which makes more sense to me because pulses per mile will be dictated by the differential ratio and the height of the tires. Using a 26" tire, a 3.08 ratio, and the 40 pulses per driveshaft revolution, tell me if this math is correct for converting pulses per driveshaft revolution into pulses per mile:

Feet traveled per tire revolution = 26" / 12" = 2.167'
# tire revolutions per driveshaft rotation = 3.08
Feet traveled per driveshaft rotation = 3.08 * 2.167' = 6.673'
# driveshaft rotations per mile = 5,280 / 6.673 = 791.2
VSS pulses per mile = 791.2 rotations * 40 pulses per rotation = 31,650 pulses per mile (compared to 40,000)

I'm probably way off base here, but I was just curious.

As for the code patches you mentioned...man, that goes over my head FAST. I think the thread states that this code is located on the EPROM, but that's confusing to me because I thought that my 32K chip was only large enough to hold the binary file (unless you mean it is located within the binary file). I'm really eager to learn all about programming, but I'm just now cutting my teeth on burning updated binary files on my EPROM...I probably just need to pace myself.

SO, I guess I'll go ahead and fork over the $80 for the Dakota Digital SGI-5 box and be done with it. Has everyone else mounted their box inside the console? I was trying to think of somewhere else to mount it since I JUST got through spending a couple of hours putting my console back in the car after the T56 swap. Any other mounting location ideas are welcome.

One last thing...I'm almost positive that the GMECM software automatically recalculated the checksum for me after I made the bin edits. Also, I did have a couple of pins on the chip out of alignment the first time I installed the chip, but I have since corrected that problem. That's why I was thinking that the code 51 was still showing up from the first time. I have disconnected the battery since then though, which I thought would "clear" the trouble codes on the ECM.

Man, this reply could pass for a novel...sorry for the rambling...

 

Feet traveled per tire revolution = 26" / 12" = 2.167'

Should be 26" * PI / 12" = 6.81'

# tire revolutions per driveshaft rotation = 3.08
Feet traveled per driveshaft rotation = 3.08 * 2.167' = 6.673'

Should be 6.81' / 3.08 = 2.21' (drive shaft if spinning faster than the wheel. )

# driveshaft rotations per mile = 5,280 / 6.673 = 791.2

Should be 5280/2.21 = 2389 (this should equal third gear(auto) 4th gear (manual) RPM at 60 MPH)

VSS pulses per mile = 791.2 rotations * 40 pulses per rotation = 31,650 pulses per mile (compared to 40,000)

In the back of my mind I seem to remember 11 and 13 pulses per rev. I dont know for sure but if you want to know for sure just count teeth on the wheel.

Also I looked for the DRAC document and could not find it. I will look again when I am at home.

HTH

John

 

Man...I should have my engineer title stripped from me...can't believe I forgot that C=2*pi*r...what an idiot

Thanks for the math lesson (ha)

 

Now I have a few questions...How did you get that picture of the check list for B1, B2..etc...I assumed you use some sort of ecm scanner?

The reason I'm asking is I have a '91 Camaro and I just swapped some 3.23's for some 3.73's and now my speedo is off. It seems like I should be able to reprogram the VSS signal to tell the ECM that I am running 3.73's ? does that make any sense?


-Mace

 

Well, here's where I get to look kinda stupid...I was using the wrong mask file. I downloaded it from diy-efi.org on the page for the 1228746 ECM, so I assumed it was correct. However, it was for a 165 ECM instead.

In other words, the "checklist" you referred to was actually for a different ECM. I was using the GMECM software to edit my bin but with the wrong ecu file, which resulted in some really strange constants...guess I should have figured that out earlier. I'm glad that my error was brought to my attention (on a different thirdgen thread) because I was going nuts trying to figure out why my SES light kept flashing after I burnt a new bin on my EPROM. I haven't tried it again with the correct mask yet, but I'm somewhat certain that was the reason.

ANYWAY, I think you have two options for getting your VSS signal corrected. You can either change the speedo gears or purchase an SGI-5 Dakota Digital converter module. You can learn more about the speedo gears in the tech article section at https://www.thirdgen.org/newdesign/tech/gears.shtml...however, I think you may have some trouble finding the right gears since I'm pretty sure a thirdgen Camaro never came with 3.73 gears. Your local dealer may be able to help you out, though.

If you go the SGI-5 route, you will basically just wire it up in-between the transmission and the ECM. I just ordered one myself, so I'll be able to tell you more about it after I install it this weekend. The nice thing about it is you can make adjustments every time you change gears or tire height. It will also allow you to run a T56 6-speed tranny if you get tired of that automatic (assuming you have an auto...I think they came with 3.23s). It costs $80 compared to about $25 for the speedo gears (if you can find them).

Hope that helps...let me know if you have any other questions.

 

Yeah, that helped a lot, thanks

I have an auto, and I'm running 255's in the rear instead of 245. I plan on doing an LS1/T-56 swap as well as getting some 17's with at least 275's in the rear. So it sounds like the speedo swap for me would be putting a band aid on a shot gun wound

Let me know how the install goes and it does what we all hope it does.

-Mace

 

By the way, have you ever heard of Electronic Ratio Adapter (ERA)?

Here is their website,

http://www.transmissioncenter.net/sp...n_______va.htm

I didn't know if this was anything like the SGI-5?

-Mace

 

I think I have the DRAC PDF you are looking for.

http://kmoore.phzero.net/my%20pictures/drac2.pdf

 

Thanks for the DRAC info! That is one of the documents I was trying to find on the diy-efi site. Now for the questions:

1) It looks like this information was generated for 92-94 GM trucks...did my 1992 Camaro RS use the very same DRAC as a 1992 GM pickup?

2) Under "Method #1" the Input Ratio formula uses a 128,000 ppm output to the RWAL (whatever that is)...I just swapped in a T56 and I believe that I have read that it has a 40,000 ppm output (see my confusing post above...I still don't quite understand how it is calculated). Should I just plug in a value of 40,000 as opposed to 128,000 to calculate my input ratio?

3) Just to make sure I'm doing this right, let me run through my car's example. I haven't measured the "actual tire circumference", but let's just use a 26" tall tire for now.

RC = 3.14159 * 26" = 81.681
XR = 3.08
P = 40 pulses per revolution (is this correct for a T56?)

Input Ratio = (63360 * 3.08 * 40) / (81.681 * 40000) = 2.389

Considering that the tables only go up to a 1.977539 ratio, I guess that means that I can't use my factory DRAC to correctly convert the VSS signal from the T56...right? Or did I just make a mistake in the calculation?

4) If for some reason I CAN use my factory DRAC, where is it located? Is it sitting right next to the ECM underneath the passenger side of the dash?


One more thing...I may have been a little confused regarding the speedo gears I discussed above. I got to thinking about it and I don't even know which cars CAME with speedo gears...was it only in 700R4 auto trannys, only through 1989 Camaros, or what. I am not sure if the gears only apply for a mechanical speedo, or if they are actually used to "drive" the VSS electronic signal. Since you have a '91, I know you have an electronic speedo...I just don't know if you have any other option aside from purchasing an SGI-5 (www.dakotadigital.com) or possibly modifying your factory DRAC.

 

T56 is 17 pulses per rev. So you'd need to modify your existing ratio by a factor of 17/40. That's less than 0.5 so I don't think you can modify your DRAC. I think something like an SGI-5 is required. I guess you could half-*** it and make up the rest by a change in tire diameter...

EDIT: I did some thinking and it occured to me that it all depends what your current setting is. By your calculations, what is your current setting?

 

can anyone verify that the 90-92 VSS equiped cars, do have a DRAC on them? i did a gear change, and have been to lazy to look for speedo gears, and too cheap to by a DD box. this would be an easy fix if the electronic speedo TBI cars can do this.

 

Well my 93 Caprice with a C3 ECM has a VSS with gears. In other words, I can't change the divider in the EPROM.

 

number of tire revolutions should be 1/rear end ratio, no the other way around correct? If you have 3.08's the driveshaft turns 3.08 times per wheel rev, so wheel rev is 1/3.08 per driveshaft revolution.

Feet traveled per driveshaft rotation =.3246*2.167=.70357

 

some "pulses per driveshavt rev" info for varying trannies is here:

http://www.jagsthatrun.com/Pages/Spe...eedometer.html

The bit flags that you change on the '7730 account for the SPEEDO READING AT THE SPEEDO, there is another setting that changes the speed that the COMPUTER sees... the 2 are INDEPENDANT. the speed that the ECM sees can be more precisely set. Without doing this, if you've made the chip mod for MAX RPM shutoff, you will trip it.

I realize the '7730 chip mods are NOT what you need, but I figured I'd put this info here anyway.

I do NOT have that extra info on my site, and I just noticed that the link is dead on my new site, dzy.org, so I'll fix them and make the mods to the speedo doc a little more complete... sorry bout that.

Oh, and thanks for the kind words about my shift plate! I see in CHP, in the LS-1 swap article that my plate is mentioned, although no one else but me whould have even known :/

I still sell about 1 per month average... with no advertising, lol...


-Dave Z

 

It's very easy to tell if you car has speedo gears or not. If wire is going to the tail shaft housing, you don't. No 93' cars will have gears. I've seen jap cars with gears to drive a sensor. WTF
Trucks came with 3.42, 3.73, and 4.11. But 28" tires. Bins for trucks may have the settings you need. A 3.42 with a 28" is very close to a 3.08 with 26's. A 4.1 is about a 3.8 though.
This won't help your speedo problem unless they use a DRAC too. Which I assume they do.
This site is fun, I learn something new everytime I'm here. Now I have something else to go find in my bin.

 

Did you mean F-body or all GM MY1993 vehicles? And are you talking about a gear-driven speedo or simply a VSS that is gear driven off the tailshaft, instead of a magnetic pickup?

 

93' 4L60/4L60E cars and trucks. I try not to work on front drivers.

I have seen gear driven VSS w/ a cable
drv speedo on jap cars.

Anyway, if you have a cable, you will have gears. Wires, probably not.

Stock anyway. There's an aftermarket VSS driven cable adapter too.

I haven't checked to see if a cable drv fits a VSS case yet. Looks closes at a glance.

 

I guess what I was getting at is that my 93 Caprice VSS is gear driven off the tranny's output shaft. I think it performs a mechanical-electrical conversion in unit and sends that to the DRAC under the dash...So I would have wires coming out of mine. Yet there is actual contact with the output shaft with gears.

 

I use the Dakota Digtal SGI-5. It will not only correct the signal, but also comes with a calculations table to fine trim your correct speed via the switches on the box itself. When you get it accurate, a speedo correction required for a gear change is just a switch away! It works great for me!

 

I've heard they don't go bad too often, but can be "hurt" during an improper installation, and that the company isn't too willing to work with you on warranty replacement. Again, "hearsay", so if anyone wants to offer any first-hand warranty experiences please do.