Car is '96 lt1 camaro, pretty much stock. New plugs and wires. I threw the P0430 first and the cat started rattling. Then I had to drive the car to school twice last week because I had no other choice and all of the sudden while i was driving it i started getting a misfire. I scanned it and pulled the P0300. I looked hard for burnt plug wires and arcing and they all look great. I am probably going to do a fuel pressure test tomorrow after I buy a guage. Any suggestions on what to check before i start throwing money towards a new opti and etc.

 

Right, don't start throwing parts at it, and your problem isn't the "opti and etc." anyway.
The PO300 random misfire is more than likely a side effect of what's causing the PO430 code. Take care of the PO430 problem first.
Here's what it means, and what to look for (btw, bank 2 is the passenger side): OBD-II Trouble Code: P0430 Catalyst Efficiency Below Threshold (Bank 2)

 

i would think the missfire is the cause of the cat failure. i would look at the 300 first. so only the two codes? how old are the plugs, plug wires, opti, 02 sensors?

 

Chicken or the egg?
Probable causes of the PO430 code:
1) Malfunctioning cat converter
2) Malfunctioning oxygen sensor
3) An exhaust leak
A PO300 misfire could cause #1
But #2 and #3 can cause a PO300 misfire
PO430 wins best 2 out of 3!

 

i have verified the cause of the P0430 It is the cat. The front bank 2 02 isnt throwing codes and the rear one has been changed in the past few months, thought that may have been the cause of the P0430, but Everything was normal on the scanner/ live data otherwise. The cat started rattling. Probably the result of a spark plug wire that was bad outta the box that had me fooled for a little bit a few months ago lol. Probably too much raw fuel.

The plugs and wires are a couple of months old and have like 1000 miles on them.

My fuel pressure test was 26 psi-key on
38 psi-idling
I believe thats normal. Right? My dad has a spark tester that clamps on the plug wires so im gonna see what that tells me.

BTW a new cat is on the way. But I wanna make sure that the misfire isn't being caused by another problem.

 

Sometimes the cat can break apart from old age and use (miles), the chunks turn around inside, causing a restriction and other issues back up the line. Or, running rich can over tax the cat and cause a melt down/breaking apart. When you had a bad wire for those few months, was a misfire code thrown? But typically, a bad wire would give you a cylinder specific code, like PO304 as an example.

 

fuel pressure is a tad low, should be 37 or so at idle and 42 when fuel pressure regulator hose is unplugged. should also go to 42 when key is turned on.

 

the wire was bad for a couple of days before i was able to scan it and i pulled a P0300 but when looking at live data i was only misfiring on #6. After that is when i started pulling the P0430. Im going to get a spark tester on each wire to see if I can narrow it down.

 

Hmm, why would my idle fuel pressure be normal and my key on pressure be low? I don't think fuel delivery is the problem though. The car stays consistently at where it should be running. After I investigate my spark more i will see if that is the issue.

 

Snow kept me from working on it any today. Hopefully tomorrow or the next day.