Effects of LPG on Catalyst

Hi,

My mk1 with OBD2 LPG is throwing "16806 - Main Catalyst; Bank 1 P0422 - 35-00 - Efficiency Below Threshold" MIL. I was inspecting this on VCDS (e.g. on idle) and rear O2 shows high oxygen levels (low voltage – around 0.15V) and low temperature (320C on idle). If I switch to petrol, voltage immediately goes up to 0.55-0.65V showing low level of oxygen in the exhaust and the cat is working fine according to data and fuel trims. If I run it only on petrol, there is no Low Efficiency MIL. Since I have the LPG software too, when I increase the amount of LPG (e.g. on idle), rear O2 voltage goes up for a brief amount of time (showing low oxygen levels – as it should be) but very quickly goes to low voltage again. As an end result, increasing the amount of LPG only reflects to short and long term fuel trims making it richer or leaner, but when these trims stabilize, there is always high oxygen levels in the exhaust leaving negative (or positive) LTFT for Idle or Part Throttle in VCDS Engine Block 32. Increasing or decreasing amount of LPG fuel reflects only on high/low fuel trims readings, but not on proper catalytic functioning which confuse me, ALOT. Somehow, whatever LPG MAP is designed, there is always high levels of oxygen in the exhaust.

Bosch waste gate coil and cables, including NGK spark plugs and sensors, are brand new and OEM.

Anyone have an idea what to do here?

Edited 15 March, 20206 yr by mister8ight
typo