97 k1500 engine code

[Hotrod]

Hi everyone, ive had this truck for about a year and half now, its a 5.7. Put a different engine in the truck after I bought it, went thru it and resealed it before I stuck it in. Started having an issue the beginning of this year with a code p0430. Replaced the downstream sensor for bank 2 and it didn't do anything. Catalytic convertor reads about 125 degree warmer coming out as well as the driver side also. I compared the two. Truck has 285's and gets almost 16 mpg. Code keeps reoccurring and I'm tired of looking at it and erasing it. just not sure what else to check. thanks for any info on what to check

 

[Supercharged111]

Either the cat is junk or something is pissing it off. How are the O2 trims from one side to the other?

 

[Hotrod]

I haven’t checked the trims yet. How do i go about checking the trims? I have a code reader that does live data. Would that possibly work? Ive just never messed with it, thanks

 

[Supercharged111]

Yeah, watch long term fuel trims (LTFT) while driving. Or have someone else watch it while you drive.

 

[Hotrod]

Ok so at 2000rpm while driving ltft 1 is 2.3 and so is 2. At idle which is 600-650 rpm ltft 1 is -11.7 and 2 is -14.1

 

[Supercharged111]

Idle LTFTs seem a little over the top, but cruise seems less off. I'm under the impression that cruise should be slightly negative as well. How un-stock is the motor? And can any other stock owners compare these values to their own?

 

[Hotrod]

Ill see if i can get any other stock owners data and the engine is completely stock nothing’s been done to it.