I just put a 2002 5.3/4l60e into my 1994 full size P/U. I have a few bugs to work out-just got it fired up for the first time about 6 hours ago! Anyways my speedo is inoperable and I was wondering if anybody on here has ran into this. The truck has a DRAC module that controls the speedo and I hooked the VSS out wires from the 2002 PCM to the VSS in on the DRAC but the needle doesn't even attempt to move. Is there something I have overlooked? I have a couple other issues, but the speedo is the main thing. I hope to have it all done by Friday and start putting some road miles on it.

 

That would be hooked up wrong. You need to find the VSS out of the DRAC, cut it, and hook up the LS1 PCM VSS out to that. Then the speedo will be fine.

If you had ABS on the truck, it won't be working now because the DRAC is out of the picture. The DRAC needs to see the VSS signal from the back of the transmission if you want the ABS to still work.

 

So you are saying that the signal coming out of the 2002 PCM is "processed" already and that it could go straight to the speedo. OR another way is to hook the raw signal from the VSS at the back of the tranny to the DRAC and then let the DRAC process the signal and send it to the appropriate places through the existing truck wiring? The latter is what I would prefer if it will work. (thats what I thought I was doing already)

 

Yes, the newer PCM's do all of the processing without using DRACs or other VSS buffer boxes. To make everything happy you need to tap into the 2 wires from the VSS and let the DRAC get the signal, AND the new PCM get the same signal. On some applications you have to watch that the VSS signal doesn't get pulled too low because two devices are tied to it.

 

I took the feed from the PCM to the DRAC and everything works great. Just watch your wiring. PCM low is the ground circuit at the DRAC.

Keep us posted.

 

I found the prob-I forgot to plug the DRAC back in after having it unhooked testing continuity of some of the wires. I feel like an idiot, but at least I am smiling 'cause it works now!

 

I think most of us are guilty of something like that occasionally