Disable 4-6-8 engine
 

I have an 81 with the 4-6-8 engine. I would like to know how to disable to 8 cylinders only. Can any one help?

you need to look on the side of transmision above the transmission pan for a wire harness with black wire and just cut it. Its the terminal that makes a connection when you hit 3rd gear. it is the one that you want to disconnect to eliminate 8/6/4. It will not set a code when you disconnect the wire. Some people have used a toggle switch for this so on long trips they could get better mpgs.

8/6/4
 

When I was changing my ECM I found one that was for the same engine but without the 864 function and that did the job also. Rebuilt ECM was around $200 and I got better performance as well.A little more pricy way to go but an alternative.