matty b

Hey, Im tearing my hair out trying to diagnose an issue on a car I did an LS swap into. Recently I went to fire the car off and found that the tach was inop. Checked codes and got P0654 Engine Speed output.

First things first I did a WRITE ENTIRE on the PCM and retried it , no good.

So pulled down the PCM and the cluster and checked my circuits. I have good voltage and ground and the tach lead has continuity from the pcm connector to the TACH no short to power or ground either.

I called Classic Instruments who made the gauges and asked tech help what to check. He suggested using the VSS signal to the speedo and hook it to the tach. When doing this the tach moved with speed.

Thinking that the only thing left in line would be the PCM, I installed a new flashed PCM with only the VATS turned off and retried. Again it did not function.

Now Im at a very bad spot as I dont know where to go with this. I was given a suggestion to try a pullup resistor on the tach lead and Im close to trying that however Im doubtful thatll work as the tach read perfect for quite a while prior to this happening.

If there are any and I mean ANY please please chime in. Im chasing ghosts now and Im concerned that I may not get this worked out.