Hey guys, I posted this over in the Gen III External Engine section a few days ago without any answers and am hoping for better luck over here... I'm going to be using a set of C6 LS3 exhaust manifolds for swapping a 5.3/4l80e in to my '89 K5 and had a couple of questions about the O2 sensor locations. The C6 manifolds have the O2 bungs built in above the outlet flange instead of being in the exhaust piping 6-8" down stream of the outlet like on the donor truck. Will them being that much closer to the engine affect anything (like tripping the CEL) or require any additional tuning for them to read correctly since I'm using the 0411 PCM from an '02 Silverado? I've been searching around on here and other forums but everything I'm seeing is for people moving them further downstream or installing wide band O2's... Here's what the C6 manifolds looks like for reference:




For the rear O2, is there a set distance it needs to be from the engine or cats or do you have some wiggle room? I've heard they can be pretty finicky and trip CEL's if they're too far away but haven't been able to find out if there's a sweet spot that it needs to be in yet... On my donor, it's on the DS exhaust tube right before they merge at the Y so I'm hoping to keep it pretty close to that when we run the new exhaust in the K5 but I'm not sure how that'll work out looking at how ugly the current exhaust is ran to fit around all of the 4wd stuff...

 

I put a 5.3 from a 2003 into a 57 pick up and put only 2 O2 sensors in (Bank1 sensor 1 and Bank 2 sensor 1). One on each side about a foot from the collector and had no CEL issues. Be sure you put the correct harness on the correct side! That was my only issue. I mixed them up and had one side running lean and the other was so rich it fouled the plugs. Switch the O2 wires and it ran great.

 

Thanks for the reply. I'll need to keep all three sensors for mine since I'll be having to deal with a CA smog ref inspection once the swap is done... Funny thing is the rear O2 is the one I'm the least worried about since it should be relatively easy to keep in the same general spot on the new exhaust (fingers crossed anyways). The front O2 sensors are the ones that I'll be most worried about since they'll only be around 6" from the exhaust port on the head with the LS3 manifolds versus 16" or more on the stock truck that the computer is from... If I have to I can re-use the down pipes from the truck with a new 2 bolt flange so I'll have the sensor bungs in the original location and then buy a set of bung plugs for the manifolds. Hate to do that if I don't have to though...