Hey everyone so I had a severe misfire issue for a while. Ended up being a combination of a burnt exhaust valve (which I repaired) and a set of bad aftermarket injectors that were leaking and causing the engine to run extremely rich. The overfueling was throwing everything off and making the ECM act erratic.

Now that’s all fixed, the car runs great, smooth idle, no misfires, and revs clean!

After a 200+ mile highway drive, I got a P0420 (catalyst system efficiency below threshold B1) code. Car still runs perfectly fine with no drivability issues. The code showed up after I got it to highways speeds (60-80MPH)

I am wondering Is it likely the catalytic converter that is just contaminated from the previous rich condition and might clear up with time, or is it usually permanently damaged at that point?

Appreciate any input. I really would like to enjoy the car without seeing the check engine light on every time I get behind the wheel.

 

Considering you've replaced valves and etc it would be best to replace the converter at this point and the oxygen sensor. Try using a fuel cleaner but chances are it's damaged more than likely from how it previously ran.

 

The only thing that makes me hesitant to jump straight to replacing the catalytic converter is that the car is running extremely well now—smooth idle, no misfires, no loss of power, and it revs clean. That’s what’s throwing me off.

I understand the converter could have been affected. But the drivability isn’t being affected at at all so I’m wondering if it’s just that the cat is still contaminated and it may recover by giving it more drive cycles or trying a cleaner like you mentioned before replacing it.
Would the fact that it only set the code after steady highway driving point more toward borderline efficiency rather than complete failure?Just trying to avoid replacing it prematurely if there’s still a chance it can clear up.

 

Giving that it only codes for converter after steady highway driving, I would say it is contaminated from the previous issue. A bad converter left unaddressed could cause damage to exhaust valves also. That may have played a part in the issue before.

 

How can I confirm that the converter is bad or contaminated??? I definitely don’t want toast the exhaust valves but also ain’t trying to get a new converter if I have a good one…

 

There is several ways to check for a bad converter. If you have a scan tool and your familiar with data list reading's you could see what fuel trim levels read once at operating temperature. Also compare upstream and downstream sensors. The other way is to do a back pressure test. The easiest way to check is removing it and visually inspecting the converter and doing a tap test so you could hear if it's broken up inside.