It all started with 1 p0420

[Osei]

A long story.car 2.5I 82k miles

Got the P0420 3 weeks ago.Guess it was time for an O2 sensor or something. Checked out sources and decided on www.oxygensors.com .

Needed another week because of outstanding commitments for funds.I drive 40 miles roundtrip to work.

Car started to lose power and would not rev past 3-4k. Got it to dealer and was told misfire on all 4 cylinders. Had just replaced plugs and wires within the last 3 weeks. So was told the coil pack must be bad. Got coil pack and installed. Same issues.NGK's were not in stock and didn't want the E3's again. Not a bad plug, but you have to change by 30-35K. I didn't do mine til 37K and one of the electrode triangular parts had disintegrated and I was praying that it had burned up rather than running a piece of metal inside the cylinder. I fished with magnetic probe and found nothing. Onwards.

Got NGK's and replaced on GP. Still the same. I remember having a similar issue years ago with a chevy malibu wagon. In that case the car had run rich and burned inside the cat and fused the silica pellets. The cat would get red hot and you had to watch what you parked over! Got it to a mechanic who gutted the cat, reinstalled and all was well.

In these days of O2 sensors, car PCM's etc all is not as simple, but I checked anyway.

Removed exhaust after 1st cat, turned on car and hit the pedal. Whammo, red line as often as I wanted, although with a lot of noise!

End result, the 2nd cat is partially clogged. Am trying to run rods down it now to bust up material. Because of the bends, not sure how successful I'll be. If unable to gut it, I'll take it to a muffler shop and have it cut out and replaced with straight pipe.

 

Moral of the story. If you get a P0420. Get it remedied before you have other issues.

 

Will update after I get this resolved, one way or the other.

 

O.

[GEE-OTTO]

well a cat should last as long as the car with that said something upstream caused this issue. IF you chop out the cat then go ahead and replace it with a resonator to keep the rasp down

[nightmonkeygt]

I've been driving around with the P0420 code for atleast 6 months now. I replaced both 02 sensors and coilpack. The sensors fixed the misfiring on cylinder 2 but I my CEL kept coming on.

 

I haven't tried to diagnose it further because I just passed emissions on it and my mechanic just told me to drive it for since it's not causing any problems. However I have noticed at idle the car can get a bit shaky rarely. It's only in D but is fine if shift to neutral or park.

[Osei]

ok.

 

Took exhaust to local mech. He cut it, gutted the 2 nd cat and rewelded it, so that all lined up.

 

Engine revs freer, not sure how top end is affected yet.

 

No auto engineer, but I am leaning towards the following.

Front O2 sensor went giving bad readings. Rear working properly sends info. PCM seeing the increase in O2 ( since it works on a difference between the two sensors) sends more fuel. Car running rich and the extra fuel is consumed between the first and second cat. The extra long term heat, starts to fuse the catalyst enough that it impedes the exhaust flow.

Now you have too much back pressure and the engine starts to misfire and will not rev past a certain point or under load.

 

So it seems like classic misfire in the ignition system, but when all is replaced , its still there. once I dropped the midpipe and it revved freely, the problem was found and the solution evident.

 

That's all for now.

 

The problem with driving with a constant CEL, is that if something really malfunctions you'll not know it and bad things can happen.

 

O.