@ Blueguy
No, no Mods
The plug that was pulled looked ok, little light brown on the end, and running 91 octane
I changed the crank position sensor, prior to that had cylinder 3 coming up, now that's gone, and replaced with cylinder 5 error code.
Do not know about the Cat ... it's been on since I have had the car, year and a half, rest of the exhaust system has been replaced though. Is there a way to check it?