So the 305 in my 96 is a POS (surprise) and found a 44k 2000 K3500 with a sweet running 350/NV4500. I know the motor is a direct swap, but I'm lost on is the O2 sensors. The 305 still has 4, but one on each bank, then one just before the cat then one after. Where the 350s have two pre and post cat. The 305 has a single cat, the 350 has 2. I plan on running the 305 ECM till I find I find a 350/4l60 ECM, not doing the 4500 swap till later. Not sure how its gonna work out with the O2s...
CK5
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Vortec 305 to 350 swap
- Thread starter b454rat
- Start date
Stomis
Professional Amateur
Basically the theory behind this is that the pre 02 sensor on the 305 is more than likely due to the distance the cat is from the upstream sensors since the cat isnt til it merges. On the 350 with individual cats the placement should be in close enough proximity to the upstreams that it provides an accurate pre cat reading as well as readings for ecu adjustments.
Thats all well and good but if you run the 305 computer with the 350 exhaust its still going to be looking for the designated pre-cat oxygen sensor. You can either weld a bung next to the upstream sensor on a side and add it in, or check your part numbers and if they are the same you could simply splice the signal wire from the precat plug into one of the upstreams.
Be aware you are going to be missing a downstream sensor in your computer when you switch to the 350 computer unless you can find a tune for a year that had a merged exhaust.
Thats all well and good but if you run the 305 computer with the 350 exhaust its still going to be looking for the designated pre-cat oxygen sensor. You can either weld a bung next to the upstream sensor on a side and add it in, or check your part numbers and if they are the same you could simply splice the signal wire from the precat plug into one of the upstreams.
Be aware you are going to be missing a downstream sensor in your computer when you switch to the 350 computer unless you can find a tune for a year that had a merged exhaust.
It shouldn't be hard to find an ECM for what I need, so shouldn't have any issues...key word shouldn't 
bronc3buster842001
1/2 ton status
I have an ecm...
Whats the number on your ecm now.. Ill see if the one i have is the same..
Whats the number on your ecm now.. Ill see if the one i have is the same..
That would require walking outside to get it, and right now I don't want to!! LOL just got home from long pissed off day of work...I can get the ECM easy enough and prolly for free....thanks tho
