2000si2001lx

The car is a 2000 si with original motor. When I got the car it smelled like it was running real rich and had a check engine light on. I got home checked code and it was p0420 (inefficient cat?) I pulled the plus and they were all pretty dark and had oil around the threads. I cleared the code drove it for a day and when I rechecked plugs they were all now white in color (that L shaped piece you gap). I was noticing that the rich fuel smell was gone but the car looks like it was burning oil bad and just didn't notice the first day because it was dark out. I especially notice clouds of oil exciting the exhaust when i allow the car to coast down long hills while leaving it in gear and then hit the gas. I'm guessing this is from all the back negative vacuum created during engine braking but I'm not clear as to if that means that the Rings are the only possible cause? After driving for a day code 420 comes back on and only once I got code p130 to come up. If I leave these codes on does it cause the car to run rich because it seems to start having a fuel smell at that point. Do the white plugs mean water in cylinder? I would imagine burning what looks to be a large amount of oil would leave the plugs with a wet, dark tip?

What I have done so far is a compression test and it was horrible, 145/90/120/140 but im still surprised not one plug looked dirtier or different than the other. I was going to check by doing a leak down test just to make sure I narrow the problem down as best I can before taking it somewhere but am a little confused on if I can convert my compression tester into one or if maybe autozone rents them? Also can I check comoression change after adding oil into the cylinder like I hear a lot of people do to see if the Rings are the problem or will I cause a problem since I most likely already have oil in my cylinders?

The car has 92k original miles (from the car fax it seems legit cause the mileage was recorded and had steady increases). It has dc header, high flow cat, and exhaust + intake. Is it rings, head gasket, valve seals... if its rings can I get away with just getting a re-ring kit?

2000si2001lx

The only reason I can think of for having all the spark plugs to be white is running to lean. If I reset the CEL every time it comes on does it cause the computer to revert to stock mapping and
cause it to figure out that it's getting less restricted air flow in and out of the motor before adjusting accordingly? Either that or or possibly the oil being burned is causing the 02 sensors to think that its running to rich and telling the computer to go leaner?

Lizardslap

check your mechanical timing as well as do a leak down test idk if you can make one from the compression tester