2001 Pontiac Grand Am 3.4L V6
P0420 Catalytic Efficiency Bank 1 code was tripping every 15 miles.
After replacing the thermostat which involved re-aligning the crossover exhaust pipe (no leaks) and torquing to specs AND switching to 89 octane the P0420 would trip after approx. 22 miles.
After new spark plugs and new spark plug wires I got almost 40 miles before the P0420 tripped. PCV valve is good and good vacuum. The more I tune the longer it takes to trip. What is/are the possible issues?
Saturday, April 9th, 2011 AT 4:39 PM