I've searched and have been unsuccessful in finding an answer. I'm currently getting a 2006 GTO LS2 put into my 1986 305 TPI IROC. This car was originally built to Canadian specs. The shop is having a problem getting the original tach to work properly. They say when they hook it up to the ECM, the car begins to run really bad. They ended up frying two ECMs trying to figure out what's wrong. They were told that the 1985 and 1986 tachs are different than the other years. They were told they had to buy an adapter of some kind to make the tach work. Does anyone know how to wire up the tach? Is the adapter really needed? Thank you.

 

Sounds like they are either using the wrong wire from the PCM, or hooking it to the tach incorrectly.

 

take a look at the second pic in my post #150 in my LS3 thread

https://www.thirdgen.org/forums/ltx-...ne-swap-3.html

this is an LS3 E67 ecm, but yours will be similar idea... basically you need a pull up resistor (5K ohm or so) that is connected to ignition source to pull up the signal when it floats.

so one side of the resistor is tied to ignition the other side to your tach out from the ecm and then going to your tach gauge... in the case of my '85 IROC that was C100-D6 on the big driver's side bulkhead connector

i am sure pocket or someone can give you the exact LS1 ECM pinout

 

He'll need the LS2 pin-out.