2013 Accent 1.6 GDI 255K miles. 20K ago I replaced converter. Within that time I've replaced plugs, coils, cam and crank sensors, O2 and AF (Lamba) sensors. I'm getting an intermittent 420 code and wonder if it could be a rich condition causing it. I base this on the following numbers from my scanner: STFT = -0.8 LTFT = 7.8 Downstream O2 = 0.670 Upstream Wideband Lambda = 0.961 Upstream mA = -0.15. I tested that the O2 and Lambda sensors are working by snapping the throttle and confirming a brief lean condition and by using propane in the intake I induced a rich condition. I've confirmed that the PCV and fuel tank vapor line aren't the cause of the rich condition. I can see the MAP sensor reading as expected while driving.

Could it be a fuel injector issue? Barking up the wrong tree?

Thanks

 

Is this an OEM catalytic converter or aftermarket?

GDI engines have their specific set of issues: The inlet valves don't get cleaned by fuel. therefore they build up much more carbon deposits than port fuel injected engines.That leads to misfires and rough running. Misfires means unburned fuel is going into the catalytic converter. Even more so when the engine is cold. PO420 means warm-up efficiency below threshold. With that kind of miles on the car I wouldn't be surprised at all if that was the case here. You could use a mechanic's endoscope to have a look at the valves or go straight to a cleaning procedure.

In fact I wouldn't be surprised if any other fuel related systems are worn out.. If I understand it right there is a regular fuel pump followed by a high pressure fuel pump and followed by an injector. All of which experience wear over time. I am not able to tell which one is most likely responsible for your troubles.

By the way these deposits on the valves come from the PCV system. They are being installed in order to burn the vapors rather than letting them out into the air for everyone to breath. the more wear you have on your engine the more vapors will go through that system and the quicker your intake valves will cake up.

It's complex. I found a great video that tells it in detail. I am afraid you won't like it though.

 

Thanks for the response. The car runs great. No misfires. Daily 150 mile commute so the miles add up. Best car I've owned.

 

That's great!
Still something isn't quite right or you would not have posted here. I would try a good fuel injector cleaner and CRC GDI IVD Intake valve and Turbo Cleaner. Doesn't matter that youdon't have a turbo.
https://www.crcindustries.com/how-to...turbo-cleaner/

If you do this a week or two apart you will know better which procedure had which effect. Make sure to use a low evaporation oil as the video suggests.

all the best.

 

Thanks! Yes, trying different cleaners this month.