afaik there were two systems available, ca emissions and NON CA emissiong (48 state is the term iirc)

CA emissions has 4 o2 sensors, 48 state systems had 2, in 2000 there was an extra setup with 3 i have heard, but never seen in person.

 

I've got one of those 3 systems, it has two for each bank like normal and one right after the cat just before the muffler. I would imagine 2000 wasn't much different from 1998.

 

Nope, most '98s have 2 sensors systems (non-CA)....

Per '98 FSM:

 

Ok I text him last night, and he stopped by in the morning and checked the codes. Before any work done it was throwing 2 codes, o2 sensor bank 1 sensor 1 and o2 sensor bank 1 sensor 2. Had the previously stated work done, brought it home then started doing it again. The code it had this morning was p0172 I think, system running rich. Went to his shop later today and we changed the pre cat sensor to a brand new one, seems to have done the trick runs good.

I had a little hesitation at a stop sign but it seemed to correct itself nicely, not like before were it would want to stall and lose power sputter and pop. I am going to go ahead and change the post cat sensor also, it looks just as old as the other one.

I gonna do a upper ball joint tonight.

 

You should reset the pcm so it will learn with the new O2 sensors.

Old_School I'll crawl under it this weekend and check, but I'm fairly certain I've got 3. Did it show how many pipes flow into the cat? I've got a dual inlet cat with a single out.

 

I posted a copy of whats in the manual.... if indeed you do have a 3 o2 system then its rare... as stated above.. i also never seen one before but, know there are a few out there.

Irondime: in regards to the issues.... check to make sure your park/neutrel switch is good and connected. I presonally had an issue where the truck was bucking/lack of throttle response... turns out that the wire for the switch had came in contact with the tranny and melted. once i replaced the wire all was golden.

 

i was going to offer the idea that maybe 3 sensors was CA emissions for pre 2000 and 4 was 2000+, i know the 4.7 CA emissions is 4,

 

That could be a possiblity too.... now im curious...