i was thinking of just replacing my o2 sensors since i am replacing all other sensors on the truck, IAC,TPS,MAP, CPS. Is there One sensor that does more work than the other as in truck efficiency? i don't care about ones that are just for emissions. Also how many are there if i were just do them all?

 

Change all at the same time. Maintenance is cheaper in the long run when done properly.

 

i was leaning towards that route, how many do the 5.9's have total?

 

Federal emissions have 2. California emissions have 4. I think.

 

figures, i hate CA

 

so i went under adn i do have four but i dont have a post cat one.... of the left manifold theres one the a collector and another same on the right side. then they combine into one exhaust no o2 then the cat than pipe and muffler. do i have three cats then? im so confused

 

I think you have two "pre-cats" (in the pipes right below the manifolds?), and then the 'real' cat.

 

yes that must be right they look like mini cats right below each manifold. but shouldn't i still have one after the main cat/ if not how would it monitor if the main is functioning correct. i have no codes...

 

That last one may not actually be a cat, either that, or Cali simply didn't care, so long as it was there.

 

I had a smog shop fight me back in Ca because of me not having a post cat but when I checked my stock exhaust to see if there was even wiring for it, it wasn't there. With my 95' I only had a single cat and a single O2 sensor, I know that the 2500 gassers had to cats in each manifold and another one before it headed to the muffler and had a total of 4 O2 sensors. I am assuming that 2500 exhaust systems transferred over to the 1500 as California implemented more laws in the late 90's.