jtmiller92

iTrader: (42)

So, Ive been doing some research but cant find what i am looking for. Basicly 02 LS1/T56 with 4.10 gears 275/40/17 Tires. What has to be changed in the LS1 ECM to make my 92 Speedo work right? or do i absolutley need the aftermarket box. Guy programming my ECM wrote this:

See if you can find out what needs to be changed for the speedometer. On a
LS1 t56 the speedometer settings are
VSS pulses per revolution= 17
VSS output pulses per mile= 4000
It is probably one of these settings that needs to be changed.

GMTech

The '92 speedo uses the 4,000 pulses per mile, so you can wire it straight to the computer.

jtmiller92

iTrader: (42)

OK, so your saying nothing has to be changed and my speedo will work correctly? I was under the impression it had to be changed or the speedo wouldn't read the right speed.

Klortho

You will have to have the PCM programmed with the gear/tire combo for it to read correctly, but output pulses are like GMTech said, 4000 ppm, just hook up the VSS output wire from the PCM to the speedo input where the buffer box is on the dash harness, which is under the passenger side of the dash harness. If the guy programming the PCM isn't using a program that a simple speedo calibration on it, I would get it back and probably send it to someone else so it would be right. A lot of guys where I live use Bryan at PCM4Less and love the work he does.

GMTech

Its the Tachometer that won't work right. The speedo is a 4,000 Pulse Per Mile signal, which is what the PCM outputs, so it will work wired straight to the thirdgen speedo, but like Klortho said, if you have different tires/gears then whats in the LS1 Calibration, you'll need that changed.

The Tachometer is a low voltage 4-cyl signal, so you need a Dakota Digital or equivilant to make the Tach read.

GTA91

iTrader: (1)

You guys are kidding me, right?? I used my dakote digital box I had laying around from my old 355TPI/T56 setup and wired it up. We did change my tire size and gear ratio in the LS1 PCM. I guess I can unhook it and run straight from the PCM to the speedo?? Sounds great... I may as well do that and sell this box.

*I am having some issue with my tach though... I'm using the Baker electronics tach signal converter box and my tach works fine until about 5k rpms or so and then it drops way down. WTF?!?! Anyone else having issues like this?? I guess I could use this Dakota Digital box for my tach but I don't know which output to use and what settings to have the box on. Anyone???


Thanks!

GTA91

iTrader: (1)

Also, why did I need this dakota digital box to make my speedo work with the LT1 T56 (& 355TPI setup) I used to have, but not with my LS1/T56 setup? I'm assuming the LT1 T56's VSS put out a different signal than the LS1 PCM does now? Is that right?


Thanks again!

Z28ricer

iTrader: (2)

With the T56 and your TPI computer you needed the box, because the signal the T56's VSS outputs was different than the normal signal a thirdgen vss provides the ECM. It has nothing to do with LT1 vs LS1, just that you werent using a LT1/LS1 pcm which uses the signal from the T56.

GTA91

iTrader: (1)

That's basically what I was saying/thinking. thanks man!!


Sooooooo, if that is the case... then TPI, LT1, and LS1 ECM/PCM's all output the same signal to the speedo (4000PPM), it's just that the VSS signal to the computers differ from a TPI to a LT1/LS1. Right?

Z28ricer

iTrader: (2)

Correct. Course if you want to go into it a little more the SD TPI computers output a 4000 and a 2000, the 2k goes to the cruise control box, a TBI car this happens within the buffer, the buffer gets the signal from the VSS, outputs a 4k to the cluster, a 2k to the tbi comp and a 2k to the cruise.

GTA91

iTrader: (1)

I see, thanks for the info!