Help!! I need some more suggestions. 2001 Buick Century, 3.1L, 148K miles.
Purchased a used Century about 4 mos. ago. Performed a tune-up, plugs wires, air filter, oil change. Car ran/drove good at the time, but was going through some oil. 2 mos later engine light came on (0420) related to the EGR- found the passage way in the plenum completley plugged and cleared it out and fixed code. I also replaced the intake manifold gaskets at the same time, which fixed the oil consumption. Car ran great for 2 more mos.
Just recently noticed having trouble going up hills on the highway, downshifting more often. Over two weeks, it has gotton progressively worse and now seems to lack the power to get the car up to any speed even from a stop. It will get going if I floor it and it downshifts, but it is still smoothly struggling as if towing a giant trailer. It will then slowly start to loose speed until I really step on it again. It does not buck or shudder, just seems like it is not getting enough gas or something is restricted. I am not loosing or crossing over any fluids. The cars starts and idles great, does not stall, and it revs up fine when in park- just under load is the weakness.
I have replaced the oil/filter again (synthetic), checked the air filter, new fuel filter, all 3 coils, changed tranny fluid/filter, tried several bottles injector cleaner. All had no effect and the condition is slowly getting worse. It does it cold or hot. The service engine light is not on and no codes thrown. I have had two codes thrown since it started, but I checked/cleared them right away each time and they have not come back yet. First code after changing oil and adding injector cleaner was 0410. Second while trying to accelerate down highway was 0404. Fuel pressure check w/key-on, engine off is 56psi; w/engine running is 50-52psi - both within specs.
Maybe my catalytic convertor is plugging up??- I saw another posting w/ similar problem and the cat fixed it. Would a plugged cat throw any codes?? I figure if an injector was bad, the car would run/start/idle poorly, and thus throw a code. Any ideas, tests would be helpful- Thanks