Another persistent P0420

[Just Fishing]

Probably going to be the catalyst in the end.
With the miles, it's probably at or near end of life

Many of us have also installed catch cans.
It's a little widely known these things can suck up oil through the pcv, and suck it right down the intake.

On my 5.3,
When i pulled the intake for the first time, a ton of oil started to pour out of it.

Seems like there is a catch inside of the intake, but after a while that would overflow i would assume...

Oil can poison a catalyst, part of the reason they started moving away from certain additives, and prompted roller lifters and stuff.

Now we have stuff like "hot rod oil", and "racing oil" that still have those additives for older cars.

I'm sure I'm over thinking it.

Also, did you happen to replace your o2 sensors lately?

If you do, replace all 4 at the same time.
Get oem, beware of repackage non oem in oem boxes.

 

[BG1988]

Most likely a restriction in the intake system replace the air filter most likely it's very clogged up or wrong one


I can ping the LTFT to far negative and misfire by adding an "artificial" restriction to the intake ....(i did this to ping test a FAR positive +15 sometimes spiked to +29 MAX open LTFT) (ended up being dirty fuel injectors ) I think the Royal purple is doing a good job i'm doing a 170 miles road test tomorrow better lower averages around 9-10 were like 40 miles so far

also check the MAP,baro(should match to key on) ,MAF and throttle body(could be dirty and sticking don't take apart the cog wheels just carefully open the throttle body flap and clean don't let it slam shut) make sure it works correct

it's easy to check them

 

[swathdiver]

Confirmed all 4 O2 sensors move between .1 and .9 volts. They are all moving up and down when driving. Cat Converter got as hot as 3150 F while driving. I did observe fluid coming out of exhaust but not at the end of the tail pipe like you normally see. Its leaking like right before the resonator, maybe under front passenger seat area of exhaust. I know exhaust leak was mentioned to cause issues. I wonder if this could be the culprit. Any suggestions?

Only the upstream sensors are supposed to move around a lot. The downstream sensors are supposed to stay fairly constant though they do move. When they move like the upstream, it means the catalyst is done for.

 

[TomH91]

As a wrap-up, if your money was on cats, you were right. New Walker stainless Y-pipe and cats and she finally passes emissions.

The coolant temp sensor data was valid.
The idle was smoother after I cleaned the MAF and the long term fuel trims dropped down to -4 to -6 range from -14.1.
I replaced the plugs and wires. #8 wasn’t terrible to do.
Air filter replaced.
No broken exhaust studs that I could find. Leak at rear of bank 1 closes up so fast and is so small the shop felt it wasn’t contributory.
I replaced the bank 1 rear O2 sensor with AC Delco.
Fuel pressure was normal at ide but wasn’t verified with a mechanical gauge when driving. I thought the pressure regulator might have failed internally but seems not to have been the case.
The fuel alcohol reading was over 20%, but I haven’t run any E85. The shop said the flex fuel engines sometimes have an issue where they get a bad alcohol reading and it persists and won’t reset properly. They have a customer with a 5.3 whose truck needs the reading reset every 3-4 months. They reset the alcohol reading on mine and the long term fuel trims dropped back to a normal range and stayed there.

Despite all the things I did and had the shop do, the cat efficiency code for bank 1 continued to crop up until I relented and replaced the cats. I was hoping to avoid the expense of new cats but with the miles the factory ones were pretty much aged out.

 

[Fless]

Good that you got it fixed, and thanks for posting the solution.

 

[Meccanoble]

Only the upstream sensors are supposed to move around a lot. The downstream sensors are supposed to stay fairly constant though they do move. When they move like the upstream, it means the catalyst is done for.

Thanks, the bank 2's definitely move a lot, maybe not as much as bank 1's but they definitely move. Anyone ever use Cataclean?

https://www.amazon.com/gp/product/B002BVXM92/ref=ox_sc_act_title_3?smid=A16TLDXIT2T97H&psc=1

 

[Geotrash]

Thanks, the bank 2's definitely move a lot, maybe not as much as bank 1's but they definitely move. Anyone ever use Cataclean?

https://www.amazon.com/gp/product/B002BVXM92/ref=ox_sc_act_title_3?smid=A16TLDXIT2T97H&psc=1

Yup. In my LR2. But it didn't work because the matrix had a huge hole melted through it from a bad coil causing a misfire and letting raw fuel get dumped into it. Happened before I got it, but the damage was done and cataclean can't fix that kind of damage.

 

[Meccanoble]

Yup. In my LR2. But it didn't work because the matrix had a huge hole melted through it from a bad coil causing a misfire and letting raw fuel get dumped into it. Happened before I got it, but the damage was done and cataclean can't fix that kind of damage.

I know for certain I see fluid leak from my exhaust nearer to cat, the same fluid that would probably leak out at end of exhaust. I ordered 2, I'll see if it helps. Thanks for sharing your experience.

 

[swathdiver]

As a wrap-up, if your money was on cats, you were right. New Walker stainless Y-pipe and cats and she finally passes emissions.

If you don't mind, post up the part number(s) used to help folks coming along later with these issues. Did you keep your old cats? I sold mine to the scrap man.

 

[Meccanoble]

Just want to share i added cataclean twice and after 200 miles, CEL has not come back yet and I can feel an improvement with driveability. Its like the exhaust got cleared or 02 sensors are functioning better. Less restrictions. Strongly suggest this before replacing any hardware.