2002 4WD

All 3 passenger plugs are very carbon fouled identically. All 3 driver's side are ok. This very specific symptom should rule out some of the possibilities.
Compression 155 psi all around.
Codes 0452, 0300. 0300 =badly needs tuneup, I have parts but will fix rich condition first. 0452=fuel pressure sensor, not investigated yet.
It does not have a Cat right now, that's how it came to me and is not being driven on road, was getting about 15mpg on hwy and 12 in town.
It starts and idles fine, a bit low @ 600rpm after warm up. It's running fine with plenty of power in all gears.
Replaced upstream O2 sensor with new Denso and no improvement, it's reading from .43V to 0.
Fuel leakdown tested fine, 59psi down to 55psi in 10 mins.
I sprayed brake cleaner all around the manifolds, valve covers, and vacuum hoses and there was no sign of leak.

Something upstream of the O2 sensor is dumping fuel into just those 3 passenger cylinders.
There is nothing in the fuel delivery that splits L/R (afaik). Unless all 3 injectors could have simultaneously gone bad for some reason, but I think it would be running rougher. It's not rough at all. I'm told computers very rarely go bad. I spoke to one mechanic and he suggested that replacing the plugs and replacing the cat would probably fix it, but I don't think it's that simple, and neither did the Cat guy I spoke with, and there's no sense in burning through a new Cat without fixing the problem first.
I'm considering paying someone $100 to check it out on a computer, but they don't sound confident that the result would be conclusive, would like to rule out whatever I can first. It's running fine, but burning through a lot of fuel that's starting to add up.
Thanks for taking the time to read and offer any suggestions!

 

Your fuel pressure seems a bit low to me, both the initial fuel pressure and the leak down.
I am sure if I am wrong someone will correct me since my knowledge on second gens is not extensive, but from my knowledge its not too far off from CPI first gens.
Again, I do not have experience in your year, just going on what I have read from the forum.

 

I tested at serice port by intake...from leakdown sticky: "Regulated fuel pressure must be 60psi to 66psi while the pump is running....and sustain to 55 after 10min" ...When tested at fuel filter:"Pressure must be 73psi to 108psi." Thx.

 

Regulated pressure is a tad low but it might be the pressure tester is at fault. Leakdown is fine which means the injectors are not leaking. Do the tune first and post your results. AC Delco plugs 41-993, AC Delco cap & rotor, and good quality plug wires.