For you guys that have done the LT1 swap, I have a VSS (vehical speed sensor) question. On the C220 connector of the LT1 there is a VSS wire, now is this the only wire needed to go to the speedo? The reason I ask is, on my 87 firebird there is a vss signal wire under the dash, but I am guessing that the original vss does not even need to be hooked up, or should these two be hooked togather? My car has a mechanical speedo so I bought a cable X to convert, but I cant hook it up right now because I need to get a custom made speedo cable. So can I run the 4l60e without being hooked to the speedo, will it still shift right?

 

yes, the PCM doesn't care if the speedo is connected or not.

 

What will happen is after driving above stall speed, the computer will see the RPM and no MPH so you will get a code 24 speed sensor. Once the key is turned off the light will go out until you get above stall speed again. It won't change the way the engine/computer functions just the check engine/service engine soon light will come on.

 

This is totally incorrect. On the LT1 the PCM receives the signal from the VSS in the tranny thus seeing MPH to provide a 4kppm signal out to the speedo. It will act just like it should if the speedo was hooked up and you won't get a SES light.

 

So the whole wiring loom, computer, etc is changed and no longer an 87 configuration?

 

I won't shift at all without the VSS signal with a 4L60E.

 

It will shift fine, as long as you keep the LT1 PCM harness hooked up to the tranny.

And yes, you completely remove the harness from the '87 and use the newer LT1 harness and PCM. The old '87 ECM goes in the garbage can....at least mine did.

 

people, he's talking about connecting his speedo, not the PCM. he's running a 4L60E, with the LT1 VSS and pcm. yes, it will shift fine.


On the question of running dual VSSs, I did it for 2 years. had the stock T-5 VSS in the transmission running the speedo, had a second VSS mounted on the tailshaft of the transmission reading a reluctor on the slip yoke of the transmission, connected to the PCM.

 

Klortho and texas lti were right, It shifted fine with no codes or idiot lights thrown.