On 2004 Grand Prix's..... anyone figured out how to remove the cat test?
32 mpg one second followed by 21-22mpg for several seconds with no change in driving, road level, wind, etc.... just a sudden 30%+ drop in fuel economy sucks and I'm hoping to get it figured out before the Magnaflow is plugged like the two good used factory cat's I had installed over the past several weeks.
I've checked for vacuum leaks, etc and everything is checking out good except the when the ecm runs the cat test everything goes wonkers (fuel trims, etc..).
Full tune up, new AC Delco o2 sensors, cleaned MAF, fresh topswapped engine with all new gaskets, etc... Previous owner had two engines put holes in the block over the past 200 miles he owned it and I'm not looking to go through the same.
I've changed the ICM, and next move is to try a used replacement ecm from another 04 Comp G.
