Hello all I read through the posts about people who have done the swap and no one has asked what I am thinking. My truck is a 98 chevy 2wd 4l60e the previous owner swapped in a 350 it was a 305 originally. It runs fine but I want it to be right my question is will a computer from the same year 4x4 truck suburban tahoe or 2wd truck suburban tahoe work?
It will not work unless you go to the 350s dual catalyst exhaust and 02 sensor configuration. The 4x4 PCM will not work, need a 2wd version. The transmission will not shift correctly with the 4x4 settings.
305 has a single cat, 3 x 02 sensors in front of the cat and 1 behind it. The 350 has dual cats and 1 sensor ahead and behind each cat. The 350s PCM will not be happy getting the wrong readings from the 02 sensors in the 305 exhaust. 4.3L to 350 swaps have the same problem. I have tuned a couple of V8 Astro and S10 swaps keeping the V6 exhaust, but it requires using TunerCatsOBD2 to correct the issue. HPTuners and EFILive cannot do it.
Best bet is to find a donor 350 2wd 4L60E truck, pull the whole exhaust system and the PCM. For the exhaust I would find a factory 8-lug truck exhaust if you can. PCM needs to be from a 4L60E truck though.