P0421 porbably not cat

Question

Hello

I have changed all 4 sensors (because 2of them were bad and 3rd was malfunctioning from time to time)
Code disappeared for 1000km and came back again
I never experienced any problems (like loss of power, bad idlying, rotten-egg smell) so it cannot be catalyst converter?
I'm running on LPG in my Montero Sport 2001 3.0 and I'm looking for problem and solution here...
Any ideas?

Answer 1

Was this a full conversion or set for LPG, the reason is the sparkplug for the LPG is different. Look at the underhood sticker for application for the LPG,  A sparkplug meant for LPG is different from gas