May 5, 201411 yr i have just finished rebuilding and installing new heads on my 99 forester s.o.h.c 2.5 because it had a bad miss after a timing belt change found 4 bent exhaust valves the car ran with these 4 bent valves for 40,000 plus miles.After the job was finshed the car ran like new,then 3-4 days later the C.E.L. comes on.So off to the parts store to use there scanner to check the code its p0420 catalytic converter below threshold bank 1 the same side of the engine i had the 4 bent valves.Ive read so much about this code its makin me crazy Id like to start simple and move my way foward to fix it hoping i didnt ruin the converter driving the car that long with the engine misfiring and after a lot of money into rebuilding the heads i dont want to ruin anything else by ignoring the code other than the code it runs great but i think the gas mileage could be better Edited May 5, 201411 yr by gsac132
May 5, 201411 yr Misfire = raw fuel dumping into the cats. Good chance your cats are toast. The simple stuff: Basically a tune-up. Plugs and wires, air and fuel filters. New PCV valve. Make sure you have no vacuum leaks, all of the breather hoses are attached properly and have no splits or cracks, and no exhaust leaks between the heads and the last cat. Next would be new O2 sensors.
May 5, 201411 yr Author Misfire = raw fuel dumping into the cats. Good chance your cats are toast. The simple stuff: Basically a tune-up. Plugs and wires, air and fuel filters. New PCV valve. Make sure you have no vacuum leaks, all of the breather hoses are attached properly and have no splits or cracks, and no exhaust leaks between the heads and the last cat. Next would be new O2 sensors. do you think both cats or just the one
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