The catalyst is a three bed and the amount of fuel it can convert is a limited amount.
If it provides too much backpressure the excess fuel normally burnt in the catalyst is still in the exhaust.
Adding a double dose of ChevRON TechRON, is the last a best way to allow the catalyst to clean it's self out.
http://www.chevron.com/prodserv/fuels/techrongas/
Later,