Stock tach inop

[69Chevy]

So I've searched several times and have yet to find an answer. I just got my '93 to '05 6.0/4L80 swap put back together, but can't get the tach to work. I ran the white wire from the '05 PCM to the '93's tach wire and put a 12V powered resistor in place as I've read on here, but the tach barely registers, never went higher then 1500 RPM. I grabbed GM's panel signal generator special tool from work (which is pretty much just a variable resistance tool) and ran it in place of the resistor through all ranges of resistance and it didn't change the results at all. Is there something in the PCM that needs changed or am I SOL with the original gauge? I know the 6.0 will wing a lot higher then the stock '93's tach but it just bugs me to not have it working. Thanks.

[vortecyota]

You're not sol, it can work. Assuming you did the resistor install correctly, the only thing left is the tach calibration in the PCM. If you have tune software you can play with the tach pulse cal. If not, have someone with software do it.

[69Chevy]

Thanks, I was kinda leaning towards a PCM deal, unfortunately I don't have software to tune it. I had a guy about 130 miles away tune it so I don't really know what he set up tach wise, guess I oughta call him. Then again, the tach can wait, still got other stuff to button up on it anyways. Thanks again, and I just read through your conversions thread, you do some very nice work.

[Mickeymotormount]

When I had my PCM flashed to remove VATS, I let him know that I was going to be running a stock '94 tach. Not sure if the PCM needed to be changed in order to work the tach, but mine works fine without a resistor. It may be off about 100 RPMs, but that doesn't bother me.