here is the back story.
92 Camaro RS, 305 auto.
I did an LT1 & auto trans swap. everything worked fine including speedometer. scattered the auto on the highway. Installed a T56 and now the speedometer does not work. if some one has a diagram of how to wire the T56 and a 92 speedo may be I can figure this thing out, or some one could help me out.

 

Doesn't the T56 have a different output signal/ VSS setup to the earlier trans?

Might need a conversion box like the Dakota unit

 

shouldn't need a conversion box, that is just for pre-89 camaros and pre-86 firebirds with the speedo cable as opposed to digital dash.

 

Wrong, the VSS signal from the t-56 is different from the VSS signal the stock speedo needs. You need the converter box to correct it. Or you can be like me, and use a programmable speedo and not need the box.

 

so is the VSS signal from a 4L60E from a 94 Fire bird (donor car) than the T56 from A 95 Camaro ? the speedo worked with the auto.

 

well now I know why my speedo hasn't worked, thought it did the 4000ppm out of the PCM that the dash needed, just had to route it through the factory buffer box.

 

IM unsure as to the vss signal from the 4l60e, but seeing as the speedos arent diff from auto to manual, im assuming they use the same ppm.

 

routing the vss through the factory buffer box will make the speedo move, but it wont be anywhere near right...take the car for a drive and youll see what i mean...

 

my speedo doesn't work and my tach is eratic above 3000 RPMS like there is interference. Could have sworn I read that the PCM sends out a 4000 PPM signal for the interior of the car, you just need to select auto/manual in the PCM for it to understand the auto/manual VSS, and i know the 3rd gen ecu used 2000 ppm and the gauges use 4000 ppm in the 3rd gen cause the buffer box seperates that out and re-routes it where it's needed...i'll have to dig through my schematics.

 

One puts out a "sine" wave the other is a "sqaure wave".
They do not interchange with each other.

If you used the PCM from the LT1 it should work.

 

you either gotta get the dakota box, a programable speedo, or have the t-56 machined to accept the t-5 vss...

 

not trying to hyjack the thread, but it seems like we're on the same page, both of us are using LT1 PCM and T56's, so the PCM should be issuing a 4000ppm signal that the digital gauges will understand, mine is a wiring issue, and his is something else. One thing I can do, not sure if the OP can do, is use software to see what the PCM is seeing. I forget the name of it, it was free, but when my laptop is plugged into the port, it can read live data, of which I can see that my VSS is communicating with my PCM, it's a problem between my PCM and my gauges. Can you test any live data with laptop/serial cable? At least make sure the PCM is seeing the T56's VSS signal properly.

 

I should read more carfully, i completely missed the part were youre both using the lt1 pcm's. you pretty much need the digital converter box to get the correct signal to the gauges. you just have to split the vss signal and send the raw signal to the pcm and then a raw signal to the converter box and then the converted signal to the gauges.

 

OK my Dakota digital converter box showed up today, now which lead from the T56 VSS is the ground & which is the signal wire?
so the LT1 PCM uses 4000ppm?
I think mine is a wiring issue, must have something to do with an automatic wiring harness, for the manual. I cut out the unused leads.

 

I've been following this thread and I am relatively confused now. I am in the process of starting my T56 swap (currently have a stock 305 TPI with the 4L60 auto in my 92 camaro) and from the research I have done, I seem to see that the PROMM is set for 4000 ppm (AXXC PROMM). This corresponds with the T5 which produces up to 4000 ppm. Based on the info I have found, the T56 produces up to about 17,000 ppm which is why the Dakota Digital VSS is needed. As best I can figure it, the VSS off the transmission needs to go into the Dakota Digital VSS and paired down to 4000 ppm (so that it will provide the correct signal for the ecm) and then from the Dakota Digital VSS to the ecm. This will provide the correct signal to the computer which will provide the correct signal to the speedo. Am I not correct in this assumption/process?

Given the stock 305 as compared to the LT1 engine and PCM that was talked about earlier in this thread, is there a difference? From what I read, the TPI PROMM from the 92 Camaro and the LT1 PCM both look for 4000 ppm so the process for fixing the speedo should be the same. I guess it comes down that I don't understand why it was stated in the thread that the T56 produces 4000 ppm when it produces 4 times that number of pulses (17 pulses per rotation in fact).

Anyone able to help me work through this? I thought I had it sorted until reading this thread. Also, the 4L60E auto in the 4th gen camaro produces around 40,000 ppm which is why the VSS is needed even using the LT1 PCM with the automatic that was switched out.

Thanks for the help on this. I'm relatively new to this type of work and am trying to wrap my head around it all.

 

Not on the same subject as the op but a Dakota digital sgi-100bt will convert 17 pulses or to 4k for the 730 ecm

 

Pretty sure the way you'll have to wire up the system is to use the T56 VSS,... to the DD box,... then out to the ECM,..... the ECM will feed the Speedo.
** You could probably bypass the ECM and send DD box output directly to the speedo. I *think* the only thing the ECM MIGHT uses speed for is MAYBE the auto tranny lock-up and if your going stick,... ! )

I have a digital dash in my 84 and my ride uses the the T56 VSS,. to the DD box,.. then to the Speedo. (I removed the factory VSS BUFFER and replaced it with the DD box, No ECM,... use LT1 PCM to run the Engine.)

Here is a schematic of tour TPI car speedo system,... Hope this helps !

 

The Vss needs to go to the ecm for fueling calculations and iac control or stalling or bucking will occur.

 

I have a lt1 t56 swap. You do t need anything so long as you feed the t56 to the pcm. Then the pcm feeds the gauge.

unless like me you have a 93 t56 that outputs at a lower rate than the 94s and up. My speed to reads but it’s high.

 

I have a lt1 t56 swap. You do t need anything so long as you feed the t56 to the pcm. Then the pcm feeds the gauge. You use the sgi box to adjust the pcm signal output so it reads correct at the gauge.

but the pcm will always read the correct speed even if the gauge is off. I actually don’t have a sgi box at all. I feed the gauge directly off the pcm. I have a 93 t56 that has a different signal rate than the later 94 t56s.